Safe exclusion of pulmonary embolism using the Wells rule and qualitative D-dimer testing in primary care: prospective cohort study
BMJ 2012; 345 doi: https://doi.org/10.1136/bmj.e6564 (Published 04 October 2012) Cite this as: BMJ 2012;345:e6564
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In 1995 I did a literature review on D-Dimer assays for the detection of Pulmonary embolism (PE) and came across an animal model of experimentally induced PE. Serial measurement of D-Dimer showed a peak at 1hr with low levels after 24hr.
In 2007 (1), a canine study showed a peak at 2hours. In 2011 (2), a retrospective study of patients presenting to an emergency department concluded that negative D-dimer results should be ignored if taken later than 1 week after onset of symptoms.
For the last 17 years I have always tried to obtain a D-Dimer sample 1-2hours after onset of symptoms, and maintained clinical suspician of pulmonary embolism if I was unable to obtain a sample within 24hours of symptoms. I feel any discussion about the sensivity of D-Dimer assays for pulmonary embolism should include timing.
1. The dynamic changes of LDH isoenzyme 3 and D-dimer following pulmonary thromboembolism in canine.
Ben SQ, Ni SS, Shen HH, Shi YX, Huang SB, Xu JH, Huang JF.
Thromb Res. 2007;120(4):575-83. Epub 2007 Jan 29.
2.J Thromb Thrombolysis. 2011 Jan;31(1):1-5. The diagnostic yield of D-Dimer in relation to time from symptom onset in patients evaluated for venous thromboembolism in the emergency medicine department. Goldin Y, Pasvolsky O, Rogowski O, Shapira I, Steinvil A, Halpern P, Serov J, Deutsch V, Aviram G, Berliner S.
Competing interests: No competing interests
This is a very interesting study and the introduction of point of care D-dimer testing in primary care may prove to be a very useful tool to assist in the management of such cases. However, the specificity of the D-dimer test remains low even when in combination with a low risk Wells score. The study demonstrates that even in the presence of a negative D-dimer and low risk Wells score patients can still have a pulmonary embolism. For example one of the cases mentioned is a 25 year old female, taking the combined oral contraceptive pill who presents with acute pleuritic chest pain and shortness of breath, has a Wells score of zero and a negative d-dimer, yet is diagnosed with a pulmonary embolism. There is a danger that the introduction of D-dimer testing in primary care could lead to a potentially fatal delay in diagnosis for a very small, but significant number of patients if primary care practitioners are falsely reassured by these indicators. Alternatively, based on this patient’s presentation I am sure that the majority of primary care practitioners would agree that they would have considered admitting this patient for further investigation anyway, despite her classification as low risk, suggesting that the introduction of point of care D-dimer testing could be largely overridden by clinical judgement anyway?
Competing interests: No competing interests
Re: Safe exclusion of pulmonary embolism using the Wells rule and qualitative D-dimer testing in primary care: prospective cohort study
Is d-dimer point of care testing practical in primary care?
On the surface, d-dimer point of care testing seems cost effective and convenient but will general practitioners use this technology? Qualitative point of care tests require a capillary blood sample and a positive result produces a pink line on a reagent strip, similar to urinary pregnancy tests. This can be difficult for users to interpret1, whilst also being less sensitive2 than quantitative point of care tests. Quantitative testing requires additional apparatus, calibration, greater volumes of blood for sampling and can take up to 15 minutes to process. Compounded by an environment of increasing complaints against doctors and litigation, GPs may decide to err on the side of caution and refer patients with a suspected PE to hospital.
Could a PE pathway spanning primary and secondary care be a more appropriate solution? Clinically stable patients with a potential PE could be initiated on anticoagulation in primary care and referred to a rapid access clinic (seen within 24 hours) for further assessment including CTPA if required. This would reduce the strain placed on emergency departments, avoid unnecessary hospital admissions and reduce the frustration experienced by patients who would otherwise be waiting for investigations in hospital.
1. Geersing G, Toll D, Janssen K, Oudega R, Blikman M, Wijland R, et al. Diagnostic Accuracy and User-Friendliness of 5 Point-of-Care D-Dimer Tests for the Exclusion of Deep Vein Thrombosis. Clinical Chemistry 2010;56:1758-1766.
2. Geersing G, Janssen K, Oudega R, Bax L, Hoes A, Reitsma J, Moons K. Excluding venous thromboembolism using point of care D-dimer tests in outpatients: a diagnostic meta-analysis. BMJ 2009;339:b2990.
Competing interests: No competing interests