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Rapid Responses: Rapid Responses published:
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An inefficient and costly way of managing an acute abdomen.
- Richard G Fiddian-Green (30 June 2009)
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Re: An inefficient and costly way of managing an acute abdomen.
- Wytze Laméris, Adrienne van Randen, Patrick MM Bossuyt, Marja Boermeester, Jaap Stoker (6 July 2009)
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Importance of repeated clinical examinations.
- Richard G Fiddian-Green (7 July 2009)
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Apples and oranges and opposing objectivess..
- Richard G Fiddian-Green (7 July 2009)
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A succession of examinations can be a very painful experience.
- Richard G Fiddian-Green (7 July 2009)
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Re. Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: diagnostic accuracy study.
- Masoom Muttalib, Waleed Al-Obaydi, Sobath Premaratne (9 July 2009)
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Re: Re. Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: diagnostic accuracy study.
- Wytze Lameris, Adrienne van Randen, Patrick MM Bossuyt, Marja A Boermeester, Jaap Stoker (13 July 2009)
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The limitations of non-blinded diagnostic studies in the context of imaging in acute abdominal pain.
- Masoom Muttalib, Waleed Al-Obaydi, Sobath Premaratne. (28 July 2009)
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Likelihood ratios and conclusion?
- Alexis Descatha (3 August 2009)
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Re: The limitations of non-blinded diagnostic studies in the context of imaging in acute abdominal pain.
- Wytze Laméris, Adrienne van Randen, Patrick MM Bossuyt, Marja A Boermeester, Jaap Stoker (20 August 2009)
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Re: Likelihood ratios and conclusion?
- Wytze Laméris, Adrienne van Randen, Patrick MM Bossuyt, Marja A Boermeester, Jaap Stoker (20 August 2009)
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Richard G Fiddian-Green, FRCS, FACS None
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In this study, "Surgical residents evaluated 74% (n=757) of patients, and emergency medicine residents evaluated the other 26% (264). The mean clinical experience of the residents was 25 months (range 2 months to 8.7 years). The ultrasonography was done by a radiological resident in 57% (582) of patients and by a staff radiologist in 43% (439). Fifty two per cent (300/582) of the ultrasonography examinations by residents were done during office hours under the supervision of a staff radiologist, and 48% (282) were done after office hours without supervision. The experience of the ultrasonography and CT readers ranged from one year’s residency to more than 30 years’ experience as a radiologist" (1). No mention was made of the time passed between admission to the ER and definitive intervention. In my experience in academic medical centers in the US this could be many hours and even longer than 24 hours. That all patients had blood work done prior to imaging it but one factor contributing to the delay. When my young daughter developed appendicitis whilst we were out watching the Wolverines plat a football game I made the diagnosis within minutes of returing, having been informed by my eldest daughter that she was not well, and took her to the ER having called the consultant surgeon/attending of my choice in informing him that my daughter had an acute abdomen. I then called the consultant anaesthetist of my choice telling her of my diagnosis so she could prepare the OR. The surgeon, who was waiting for me when I arrived at the ER, confirmed my diagnosis within 30 minutes without blood tests or imaging and took her to the OR. All was done in hours and she came home in under 24 hours, and that was prior to the advent of laparoscopic surgery. Running the gauntlet of inexperienced clinicians in training and being subjected to unnecessary investigations is, sadly, the rule in many medical centers today including those in this Dutch study. How much more efficient and cost-effective it could be if patients with an acute abdomen had were first seen by a consultant surgeon/attending. This is not difficult to do. In the medical center in US in which I worked consltant surgeons/attendings would be on call for emergencies for 24 hours about once a month but the patients were still evaluated by residents before they were called. It would not take much more to have them evaluate all patients presenting with acute abdominal pain. Furthermore residents could learn much by assisting in the process. Ultrasound might be a helpful addition to a consultant surgeon especially if he/she were to perform it him/herself. By the time imaging reveals anything the pathology is, however, usually fairly far advanced. More helpful might be the support of a computer progran such as that poineered decades ago by de Dombel (2). 1. Wytze Laméris, Adrienne van Randen, H Wouter van Es, Johannes P M van Heesewijk, Bert van Ramshorst, Wim H Bouma, Wim ten Hove, Maarten S van Leeuwen, Esteban M van Keulen, Marcel G W Dijkgraaf, Patrick M M Bossuyt, Marja A Boermeester, Jaap Stoker on behalf of the OPTIMA study group Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: diagnostic accuracy study BMJ 2009; 338: b2431 2. de Dombel, F. T., Dallos, V., & McAdam, W. A. (1991). Can computer aided teaching packages improve clinical care in patients with acute abdominal pain. BMJ (Clinical Research Ed.), 302(6791), 1495-1497. Competing interests: None declared |
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Wytze Laméris, Research fellow Academic Medical Center, Meibergdreef 9, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands, Adrienne van Randen, Patrick MM Bossuyt, Marja Boermeester, Jaap Stoker
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Dr. Fiddian-Green questions the (cost-) effectiveness of imaging for the assessment of patients with acute abdominal pain. Assessment of the abdomen by a consultant surgeon would be more efficient compared to imaging and would lead to a shorter time to intervention, lower costs, and better detection of pathology in an early stage. In the current study residents detected urgent conditions with a high sensitivity, but the number of false-positive diagnosis was high. In case of suspected appendicitis this will result in negative explorations. Imaging corrects many false-positive clinical diagnoses. Experienced surgeons may be more accurate and certain when clinically detecting and excluding urgent abdominal conditions compared to residents. This may reduce the need for imaging in a proportion of patients, but it is doubtful that the accuracy of consultant surgeons will be higher compared to an imaging strategy using ultrasound and conditional CT. The clinical diagnosis of an acute abdomen simply is not accurate enough for current standards of care. Even an experienced surgeon has an unacceptable error rate, which can be overcome by imaging. This has been shown for diseases like appendicitis and diverticulitis time and again (1,2). We acknowledge that in the participating centres the logistics were present to rapidly obtain diagnostic imaging and blood analysis. For the patients with appendicitis imaging was completed within a three hour time window after ED presentation. The median time from ER arrival to appendectomy was 6.7 hours. Despite an extensive imaging protocol the delay to treatment was limited and negligible compared to the pre-hospital delay, which previously has been shown to be main risk factor for perforation. In some patients with appendicitis, such as in your daughter’s case, the clinical presentation might be straightforward. However, we recently showed that only 6% of the adult patients present in a ‘classical’ way with migration of pain to the right lower quadrant, direct tenderness in the right lower quadrant, and rigidity (3). In the majority of patients making a diagnosis will be more difficult as only a few strong predictive symptoms will be presented. Clinical scoring systems and computed aided diagnosis, predicting disease based on the simultaneous presence of predictive symptoms, often have weak performance at external validation (4). As referenced in the introduction of the article, previous studies have shown a positive effect of imaging on the accuracy of clinical assessment, diagnostic certainty, and management decisions in patients with abdominal pain. Especially the use of imaging for suspected appendicitis has been investigated extensively. Randomized controlled trials have shown that routine imaging for suspected appendicitis leads to lower negative appendectomy rates compared to selective use of imaging based on the judgment of the clinician (5,6). Raman et al. reported a significant inverse relationship between the percentage of CT use and the negative appendectomy rate over a ten year period (7). In this study the diagnosis was made by emergency physicians and surgeons. Cost- effectiveness of routine use of CT for suspected appendicitis as diagnosed by surgeons was demonstrated by Rao et al (8). In our opinion imaging has proven its value for the evaluation of patients suspected with urgent abdominal conditions. References 1) Rao PM, Rhea JT, et al. Introduction of Appendiceal CT Impact on Negative Appendectomy and Appendiceal Perforation Rates. Ann of Surg 1999; 229(3):344-349 2) Laurell H, Hansson LE, et al. Acute diverticulitis – clinical presentation and differential diagnostics. Colorectal Disease 2007; 9: 496 -502 3) Laméris W, van Randen A, et al. Single and combined diagnostic value of clinical features and laboratory tests in acute appendicitis. Acad Emerg Med 2009 (in press) 4) Ohmann C, Yang Q, et al. Diagnostic score for acute appendicitis. Eur J Surg 1995; 161: 273-281 5) Lee CC, Golub R, et al. Routine versus selective abdominal computed tomography scan in the evaluation of right lower quadrant pain: a randomized controlled trial. Acad Emerg Med 2007; 14: 117-122 6) Walker S, Haun, W, et al. The value of limited computed tomography with rectal contrast in the diagnosis of acute appendicitis. Am J Surg; 2000;180:450–455 7) Raman SS, Osuagwu FC, et al. Effect of CT on false positive diagnosis of appendicitis and perforation. N Engl J Med 2008; 358(9):972- 973 8) Rao PM, Rhea JT, et al. Effect of computed tomography of the appendix on treatment of patients and use of hospital resources. N Engl J Med; 338(3): 141-146 Competing interests: None declared |
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Richard G Fiddian-Green, FRCS, FACS None
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I thank Wytze Laméris for his comprehesive response to my comments. False positives can be eliminated for the most part simply by having the original examiner reexamine the patient every hour or so until the diagnosis, or rather the need to operate or not, is certain. This is described in Zachary Cope's classic book, Diagnosis of the Acute Abdomen. Cope was a surgeon at St Mary's Hospital in London in my father's day and his book has remained a Bible for all those of us who have been trained at St Mary's since his time. William Silen, my former mentor, has edited the more recent editions of the book the current edition being, I believe, the 21st (1). I strongly recommend the book to all those involved in the diagnosis and management of the acute abdomen. I further recommend trainees committing themselves to a clinical diagnosis before imaging the patient and checking the accuracy of their diagnosis after imaging if it considered necessary. Repeat the process before the patients goes to theatre/OR and ideally go into the operating room and reexamine the patient yet again after the induction of anaesthesia and muscle relaxation and wait to see the pathology at surgery. On each case commit one's self to making a dignosis before going on to the next step. Our learning curve was aided by us living in a hostel adjacent the hospital and the sister calling us whenever an acute abdomen came in in the middle of the night. Sadly that hostel, Wilson House, is now filled with students from all disciples at Imperial so many are being deprived of the opportunities we had. Cope updated his diagnosis of acute cholecytitis by adding a new sign, a palpable but painless gallbadder, after he developed the condition. He published a case report in the BMJ(2). It is well worth reading. 1. Cope's Early Diagnosis of the Acute Abdomen: revised by William Silen Z Cope, W Silen - 2000 - Oxford University Press, USA. 2. Zachary Cope. A sign in gall bladder disease. 1970;3:147-148. Competing interests: None declared |
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Richard G Fiddian-Green, FRCS, FACS None
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"Surgical residents evaluated 74% (n=757) of patients, and emergency medicine residents evaluated the other 26%...The mean clinical experience of the residents was 25 months (range 2 months to 8.7 years)". What is the practice in Holland? Have surgical residents done six months surgery as a houseman, worked six months as a casulaty officer/ER physician and written their primary fellowship before begining their residency? What of the emergency medicine residents? Have they completed six months as a surgivcal house officer? In the US emergency physcians never get the opportunity to do a surgical job and medical students are given almost zero opportunity to scrub and learn some of the basics of surgery. Furthermore surgical residents have not done either an HS or an HP job before entering their residency programs. Even then they are heavily occupied doing "scut work" and rarely get the opportunity to get into the OR until their second and thord years. Additionally they are not required to write a primary FRCS and do not write their boards until they have completed their residencies. The inexperience of those evaluating acute abdomens in the ER today may have a lot to do with the rise in imaging. Finally the objectives of an emergency physician and radiologist are different from those of a surgeon, the former being intent upon making an accurate diagnosis and the latter intent upion deciding whether there is a need to operate or not. For a surgeon making an accurate diagnosis is more related to what incsion to use. That decsion can be deferred until after the unduction of anaesthesia and reexamining the relaxed abdomen. The opposing objectives clearly influence the perceived need for imaging. Competing interests: None declared |
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Richard G Fiddian-Green, FRCS, FACS None
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Watching some consultant physicians/internists examine an acute abdomen can be a painful experience for both parties. When testing for rebound tenderness, for example, the examination can be so rough that the patient cries out in pain and almost jumps off the bed. Its all so unnecessary. What is more the painful experience is likely to be compounded in the hands of junior trainees and repeated several times before a consultant surgeon is called to see the patient How much better for the patient to have an experienced consultant surgeon be the first to examine the patient, make a diagnosis and decide what investigations if any need to be done. Trying to define a mass ultrasoninically can be especially painful because of the need to push into the abdomen and run the sensor over the area of interest several if not many times. Transporting a patient to radiology, taking them off their trolley and placing them in and out of a CT scanner and taking them back to the ER compounds the insults as does the delay in waiting for porters and receiving definitive treatment. The chief resident and consultant surgeomn took my daughter strainght into the OR. My daughter was not given anything for pain. Opiates, which are commonly given in these circumstances, might reduce the intensity of pain inflicted by repeated insults but they are not without side effects or even risk of adverse events. Had my daughter been given an opiate after surgery, for example, she would not have been able to come home so very early after surgery because it would probably have made her sleep for hours and cause her to wake with with a pinful start by the pain inflicted by a sudden movement in the course of a dream after the effects of the opiate had worn off. Early mobility and distraction are awfully good analgesics in children. Competing interests: None declared |
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Masoom Muttalib, Waleed Al-Obaydi, Sobath Premaratne, Department of General Surgery University Hospitals Coventry and Warwickshire, UK
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Editor – The issues raised in the correspondence generated from Dr. Laméris et al. paper (1) include the experience of the clinical and radiological assessors and access to imaging facilities. These characteristics may indeed differ in other countries in everyday practice around the globe. In the methods section, ultrasonography and computed tomography (CT) were read blinded to each other. For the purposes of a research study, imaging should also have been blinded to the clinical features; otherwise the sensitivity and specificity of imaging would actually have been in combination with clinical assessment. Can the authors confirm that there was blinding in this respect? In the results section, data collection was not completed for 80/1101 patients, equating to 7.3%. These patients were therefore selected-out of the study but may have been relevant. Can the authors give reasons for this high figure? Patients discharged from the emergency department without imaging were not included in the study ie. also selected-out. These patients were either very well for discharge or had a missed diagnosis – both of which could have affected clinical diagnostic performance figures. Can the authors give any data regarding the proportion of patients that re- presented to the emergency department or were subsequently admitted? It remains important not to embrace imaging as a complete substitute for clinical assessment. As pointed out in the accompanying editorial (2), ultrasound is well-known to be operator dependent and we would add that computed tomography (CT) is known to be interpreter dependent; especially when not proof-read. There is much to applaud with making a working clinical diagnosis and utilising investigations eg. haematology, biochemistry and imaging to confirm / refute the diagnosis on a background of clinical re-evaluation. Various scoring and assessment systems for the acute abdomen are indeed surrogates for recognising the unwell patient ie. the sepsis arm of SIRS - the systemic inflammatory response syndrome (3) viz. two or more of the following parameters: Temperature <36 or >38 Celsius Tachycardia >90 bpm Tachypnoea >20 White cell count <4 or >12 (x10^9 cells/L) With the exception of raised amylase in acute pancreatitis and hallmarks of bacteruria in pyelonephritis, patients with the above features and physical signs of an acute abdomen invariably proceed to surgery as imaging would not alter clinical management (if anything, there would be a delay to surgery). However, imaging would be expected to reduce false positive clinical diagnosis especially when the history of abdominal pain has been short and SIRS parameters have not yet manifest. This is where the significant diagnostic challenge rests. Can the authors give any figures or stratify their data according to the duration of symptoms (eg. <12 hours, between 12-24 hours etc.) beyond stating blanket inclusion criteria of abdominal pain between 2 hours and 5 days duration? We are not aware of any imaging studies presented in this more meaningful way to- date. There is much to be said about extending the role of (readily available) plain radiography in imaging the acute abdomen, which was not considered in the present study. Although sonographic detection of pneumoperitoneum (4) has been described, plain radiography in the left lateral decubitus position has been recommended as an adjunct to the erect chest radiograph (5) and can detect as little as 1 ml of air without the use of CT (6). With respect to plain abdominal radiography, the Rigler sign is well-known to indicate [large] pneumoperitoneum (7) often colonic in origin. Gastrografin transit with serial abdominal radiography not only demonstrates adhesive small bowel obstruction, but can also predict the likelihood of resolution with conservative management. There is good evidence that the use of water-soluble contrast reduces the length of hospital stay in this situation (8). The present study did not include pregnant women, in view of radiation exposure from CT (although such patients might have usefully been included in a non-CT arm of the study). Difficulty in clinical diagnosis of abdominal pain in this group remains challenging. The position of inflamed viscera (eg. appendix) may alter with the rise of the gravid uterus and borderline / mildly elevated white cell counts can be expected in pregnancy. Graded compression sonography has been described in this situation (9). (1) Laméris W, van Randen A, van Es HW, van Heesewijk JPM, van Ramshorst B, Bouma WH, et al. on behalf of the OPTIMA study group. Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: diagnostic accuracy study. BMJ 2009; 339: 29-33. (2) Dixon AK, Watson CJ. Imaging in patients with acute abdominal pain: Emerging evidence points to a new sequence of investigations. BMJ 2009; 339: 1-2. (3) American College of Chest Physicians / Society of Critical Care Medicine Consensus Conference: definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Crit. Care Med. 1992; 20(6): 864-74. (4) Lee DH, Lim JH, Ko YT, Yoon Y. Sonographic detection of pneumoperitoneum in patients with acute abdomen. AJR 1990; 154: 107-9. (5) Gaines WG. Pneumoperitoneum in perforated peptic ulcer: factors in Roentgenographic demonstration. California Medicine 1953; 78(6): 508- 512. (6) Miller RE, Nelson SW. The roentgenologic demonstration of tiny amounts of free intraperitoneal gas: experimental and clinical studies. AJR 1971; 112: 574-585. (7) Lewicki AM. The Rigler Sign and Leo G. Rigler. Radiology 2004; 233(1): 7-12. (8) Abbas S, Bissett IP, Parry BR. Oral water soluble contrast for the management of adhesive small bowel obstruction. Cochrane Database Syst Rev. 2007; 18(3): CD004651. (9) Lim HK, Bae SH, Seo GS. Diagnosis of acute appendicitis in pregnant women: value of sonography. AJR 1992; 159: 539-42. Competing interests: None declared |
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Wytze Lameris, Research fellow Academic Medical Center, Meibergdreef 9, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands, Adrienne van Randen, Patrick MM Bossuyt, Marja A Boermeester, Jaap Stoker
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Editor - Dr Muttalib and colleagues comment on several aspects of our study, including that clinical information was provided to the ultrasound and computed tomography observers. It is common that clinical data are available during test evaluation in daily practice. QUADAS, a tool for the quality assessment of diagnostic studies included in systematic reviews, also highlights this issue (1) as the results obtained in a diagnostic study resembling daily practice are more widely generalizable. A research fellow daily monitored data recording and contacted physicians when data were incomplete. Despite these efforts eighty patients (7%) were excluded due to missing data. Performing a multicenter diagnostic study at busy emergency departments is challenging. The participating physicians put in great effort to prospectively record a substantial amount of data, but were sometimes practically not be able to finish data recording. No differences were found in patient characteristics or type of presentation between the excluded and the analysed patients. Discharged patients in whom imaging was not warranted by physicians were not invited to the study. Follow-up of these patients was not performed and therefore no data on re-presentation of admissions can be presented for these patients. Our primary objective was to study imaging strategies in patients in whom physicians would deem imaging necessary in daily practice, before even considering discharge. The duration of complaints and inflammatory parameters are probably important factors for physicians when deciding whether imaging is warranted. If warranted, this study showed that a strategy using ultrasound first with conditional computed tomography resulted in a high sensitivity of urgent conditions, regardless of the duration of complaints. The role of plain radiographs was considered in this study. Table 2 shows that the use of supine abdominal and upright chest radiographs after clinical evaluation did not increase sensitivity or specificity for urgent conditions compared to clinical evaluation only. Our group intends to publish a more detailed analysis of the value of plain radiographs for specific diseases soon. 1) Whiting P, Rutjes AWS, et al. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Medical Research Methodology 2003; 3: 25 Competing interests: None declared |
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Masoom Muttalib, Department of General Surgery University Hospitals Coventry and Warwickshire, UK, Waleed Al-Obaydi, Sobath Premaratne.
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Editor – We thank Dr. Laméris and colleagues for their response. There have been numerous articles by Whiting et al, with respect to the QUADAS quality assessment tool for diagnostic studies worthy of inclusion in systematic reviews, one of which Dr. Laméris cites (1). In their response, the authors were aware of the QUADAS quality assessment tool pointing to the known quality shortcomings of observational diagnostic studies, and might have strengthened their study further (2,3). With reference to quality item 11 of QUADAS: were the reference standard results interpreted without knowledge of the results of the index test? We understand that the reference standard was set as an expert panel achieving a post-hoc diagnosis (2) to enable uniformity and reduce verification bias. With respect to non-blinding of the clinical and imaging features (in the setting of a scientific study, not in the setting of everyday practice), the actual contribution of imaging to diagnostic pick-up remains unknown. The availability of clinical data during imaging is known to affect estimates of test performance, owing to the interpretative component of imaging - clinical review bias (4). However, the study does fulfil quality item 12 of QUADAS: were the same clinical data available when test results were interpreted as would be available when the test is used in practice? ie. clinical features are known to the radiologist in daily practice. It should be remembered that clinicians involved in the study could have had more hightened awareness eg. requesting imaging in cases that they otherwise would not have – also known as context bias (5). Diagnostic observational studies have the limitation of possible subconscious bias about the benefits of new technology – in other study settings, a clinician may delay making a definitive diagnosis if they know that another test is going to be performed. The unblinded interpretation of imaging may concentrate the viewer towards subtle features that otherwise would have been missed, and possibly distract the viewer from other areas of analysis (5). This would make the diagnostic contribution of imaging with respect to hightened clinical suspicion unknown. Without such blinding, we would suggest that readers appreciate that the quoted sensitivity and specificity (diagnostic performance) of imaging results are actually in combination with clinical assessment (which would also be a function of the clinician’s experience). A test would be expected to perform better in severe (advanced) disease states, as pick-up is more likely than in mild (early) pathology. Disease prevalence is likely to be higher owing to the selection of more severe (overt) cases at clinical referral. In this situation, severity and prevalence can be linked, explaining apparently high sensitivity with higher prevalence. With respect to quality item 14 of QUADAS: were withdrawals from the study explained? We appreciate the logistics of data collection for the multi-centre study explaining the rather high (7.3%) proportion of patients with incompletely recorded (and therefore selected-out) data, although the authors’ response suggests that such cases might not have been materially important demographically (although their clinico- radiologic importance remains unknown). Could the authors confirm whether data was captured manually on paper or on electronic internet (web) based-proformas. With the latter, incomplete data submission could have been avoided if the computer system alerted the user to and rejected incomplete fields. Blinding could also have been achieved with clinical / biochemical text fields collapsing down after completion, with a flag showing the radiologist that these assessments had actually been completed rather than omitted. This would have enabled quality item 11 of QUADAS to be fulfilled, and once the radiologist had completed their part of the results proforma, then the clinical / biochemical text fields could then pop-up to enable the unblinded “everyday practice” part to resume so that patients are not disadvantaged by the study process in any way (enabling quality item 12 of QUADAS also to be fulfilled). We presume that the proportion of incomplete data would have been even higher if the research fellow did not “chase-up” physicians to complete the data. Data export centrally for the purposes of analysis would also have been expedited using secure internet (web)-based electronic proformas, avoiding the need to “chase-up” prospectively collected data. We appreciate that in daily practice, a proportion of patients would be discharged by emergency department physicians (ie. selected-out) before even considering imaging. We re-iterate that within the context of a scientific study, these patients were either very well for discharge or had a missed diagnosis – both of which could have affected clinical diagnostic performance figures, especially as the decision to discharge might have been related to the inexperience of the assessing doctor. It would have been useful to collect follow-up data for patients that re- presented to the emergency department or were subsequently admitted; which as the authors’ reply states was unfortunately not recorded. This would also have strengthened the study design (6) by reducing the withdrawal (dropout) bias from analysis (4). Quoting Dr. Laméris’ response: “The duration of complaints and inflammatory parameters are probably important factors for physicians when deciding whether imaging is warranted.” As mutual clinicians, Dr. Laméris would surely agree that this is a certainty of actual practice, not a probability. “If warranted, this study showed that a strategy using ultrasound first with conditional computed tomography resulted in a high sensitivity of urgent conditions, regardless of the duration of complaints”. This study unfortunately did not stratify data according to the duration of symptoms (eg. <12 hours, between 12-24 hours etc.) beyond the general inclusion criteria of abdominal pain between 2 hours and 5 days duration. Until this is done, it remains unknown if there is higher imaging pick-up because patients with more advanced duration of symptoms are more likely to have overt physical signs and more likely to manifest SIRS (systemic inflammatory response syndrome) parameters (7) and the physician is therefore more likely to “warrant”/request imaging (context bias, described above) ! It would be important to show that the data for symptom duration was evenly distributed for the patients between the protocol 2 hours and 5 days. If it is skewed towards the latter, then the abovesaid becomes a problem. If it is skewed towards the former (2 hours) then imaging is blessed with solving the holy-grail diagnostic challenge described in our previous letter viz. when the history of abdominal pain has been short and SIRS (systemic inflammatory response syndrome) parameters have not yet manifest. With respect to extending the role of (readily available) plain radiography in imaging the acute abdomen, the second table described in the authors’ response unfortunately does not appear in the printed version of the article (3). However, we look forward to their intent to publish a more detailed analysis of the value of plain radiographs for specific diseases and hope that their study design might include the quality standards described in Dr. Laméris’ response and importance of blinding highlighted in this letter. (1) Whiting P, Rutjes AWS, et al. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Medical Research Methodology 2003; 3: 25. (2) Laméris W, van Randen A, Dijkgraaf MG, Bossuyt PM, Stoker J, Boermeester MA .Optimization of diagnostic imaging use in patients with acute abdominal pain (OPTIMA): design and rationale. BMC Emerg Med 2007; 7: 9. (3) Laméris W, van Randen A, van Es HW, van Heesewijk JP, van Ramshorst B, Bouma WH, et al. on behalf of the OPTIMA study group. Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: diagnostic accuracy study. BMJ 2009; 339: 29-33. (4) Kelly S, Berry E, Roderick P, Harris KM, Cullingworth J, Gathercole L, et al. The identification of bias in studies of the diagnostic performance of imaging modalities. Br J Radiol 1997;70:1028–35. (5) Egglin TK, Feinstein AR. Context bias: a problem in diagnostic radiology. JAMA 1996; 276: 1752–5. (6) Whiting P, Rutjes AW, Dinnes J, Reitsma JB, Bossuyt PM, Kleijnen J. Development and validation of methods for assessing the quality of diagnostic accuracy studies. Health Technology Assessment 2004; Vol. 8: No. 25. (7) American College of Chest Physicians / Society of Critical Care Medicine Consensus Conference: definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Crit. Care Med. 1992; 20(6): 864-74. Competing interests: None declared |
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Alexis Descatha, Occupational and Emergicy physician, MD PhD, UVSQ AP-HP Garches, 92380 (Paris Suburb), France
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Likelihood ratios and conclusion? Sir, I read with a particular interest the paper of Laméris W et al.(1) I have however a comment of this very high quality paper: The authors used likelihood ratios (LR) in their methodology (in order to evaluate the gain in accuracy strategy), without giving them. However, I think LR are very informative in case of evaluation of diagnosis strategies by themselves and should be given.(2) Indeed, to evaluate a diagnosis strategy performance, it is essential to know in clinical practice how a particular test result predicts the risk of abnormality.(3) The sensitivities and specificities, used by the authors, do not do this, but describe how abnormality predicts particular test results.(4) LR can be used to calculate the probability of disorder while adapting for varying prior probabilities of the chance of disease from different contexts (predictive values depend on the prevalence of the disorder). From the Table 2, we can however calculate the LR for positive and negative strategies (LR+, LR-, Table), such as the post-test probabilities for negative and positive strategies. From this table, we noticed that lowest post-test probability of a negative strategy is most accurate studied strategy (ie ultrasonography (US) first and CT only in those with negative or inconclusive US results), which is only 14.3%. We also noticed that LR+ is only at 3.0 [2.5-3.3], whereas the highest LR+ is the US for all (4.6 [3.6-5.2]). These strategies are then probably more useful for triage than confirmation diagnosis. Finally, I think the conclusion including these elements should be more explicit for the emergency physician: the authors found, in case of imaging needed for triage of non-traumatic abdominal pain and equal availability of a CT scan and US (such as the editorialist highlighted (5)), that an US study should be proposed before CT scan. 1. Lameris W, van Randen A, van Es HW, van Heesewijk JPM, van Ramshorst B, Bouma WH et al. Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: diagnostic accuracy study. BMJ 2009;338:b2431. 2. Haynes RB, Sackett DL, Guyatt GH, Tugwell P. Clinical Epidemiology. Lippincott Williams and Wilkins, 2006. 3. Deeks JJ,.Altman DG. Diagnostic tests 4: likelihood ratios. BMJ 2004;329:168-9. 4. Altman DG,.Bland JM. Diagnostic tests. 1: Sensitivity and specificity. BMJ 1994;308:1552. 5. Dixon AK,.Watson CJ. Imaging in patients with acute abdominal pain. BMJ 2009;338:b1678.
Competing interests: None declared |
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Wytze Laméris, Research fellow Academic Medical Center, Meibergdreef 9, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands, Adrienne van Randen, Patrick MM Bossuyt, Marja A Boermeester, Jaap Stoker
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We thank Dr. Muttalib and colleagues for their clear response in which they discuss several potential forms of bias related to our study. Data collection was performed prospectively using a digital web-based case record form. The duration of complaints had a unimodal distribution, with a mean of 1.7 days and. Indeed, we are certain that duration of complaints is an important factor in clinical decision making. We are aware that clinical data available during test interpretation may affect test performance. The methods section of the manuscript states that imaging was interpreted with clinical information. As indicated, it is preferable to evaluate diagnostic tests in the way they are used in clinical practice. By comparing the accuracy of the imaging strategies after the initial clinical diagnosis we were able to assess the added value of imaging, interpreted with clinical data. Our conclusion was that initial ultrasound with conditional CT after the clinical diagnosis would result in a reduction of missed urgent cases and of false-positive diagnoses of urgent conditions. Competing interests: None declared |
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Wytze Laméris, Research fellow Academic Medical Center, Meibergdreef 9, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands, Adrienne van Randen, Patrick MM Bossuyt, Marja A Boermeester, Jaap Stoker
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Dr. Descatha is thanked for the constructive response to our article. Indeed, the interpretation of the likelihood ratios and probabilities support the conclusion drawn in the original article. The proposed imaging strategy using initial ultrasound with conditional CT in patients with acute abdominal pain results in a higher positive and lower negative post- test probability compared to the clinical diagnosis. Competing interests: None declared |
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