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Does Test Fulfill Screening Criteria?
- Eithne Linnane (15 September 1999)
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Neonatal screening for MCADD
- M S Tanner (5 December 2000)
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Eithne Linnane, Specialist registrar, public health medicine North Wales Health Authority, Hendy Road, Mold, Flintshire,CH71PZ
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Editor- We welcome the report by Mushtaq et al evaluating a potential screening test for conjugated hyperbilirubinaemia in infants and the high degree of scrutiny which the authors have exercised in this feasibility study (1). However, were this test to be considered in the implementation of a screening programme, several other issues would need to be considered along with the test itself. The criteria of Wilson and Jungner (2), which have recently been updated and adopted by the national screening committee, are seen by many as the "gold standard" of screening assessment (3). Mushtaq et al do not overtly state the hypothesis which they are testing. They simply say that they wish to evaluate tandem mass spectrometry for the detection of conjugated hyperbilirubinaemia in neonates. Application of the Wilson and Jungner screening criteria before the study began, would have highlighted any potential difficulties in a future screening programme regardless of the outcome of this feasibility study. One of the most important criteria is that there must be effective evidence based and optimised treatment available for the condition being screened. Clearly this is not the case for conjugated hyperbilirubinaemia, which represents not a single disease condition but a host of conditions determined by an abnormal laboratory value. We recognise as the authors state that there can be improved survival after surgery for biliary atresia, however whether the rates of success of only 30% to 50% (4) merit instituting a screening programme is arguable. The authors state that identification of patients with increased bilirubinaemia allows for the administration of vitamin K to reduce the high level of bleeding disorders in this group. In our experience vitamin K is routinely administered to neonates so the implementation of tandem mass spectrometry would again not be justified for this purpose. We believe that the effect of proposed actions to improve the parameters in future assessment by taking the sample at 14 days and two hours after a feed would require the construction of a hypothesis examining the role of targeted blood testing rather than using available Guthrie cards. This brings us back full circle to the Yellow Alert campaign (5). Eithne Linnane Ashish Paul Ruth Parry North Wales Health Authority,
Hendy Road,
Mold,
Flintshire,
CH71PZ Competing Interests: none 1 Mushtaq I, Logan S, Morris M, Johnson AW, Kelly D et al. Screening of newborn infants for cholestatic heptobiliary disease with tandem mass spectrometry.BMJ1999;319:471-477.(21 August.) 2 Wilson JMG, Jungner G. Principles and practice of screening for disease. Public Health Paper Number 34. Geneva: WHO, 1968. 3 http:// www.doh.gov.uk/nsc/chap61.htm. Accessed 14 September 1999. 4 Okazaki T, Kobayashi H, Yamataka A, Lane GJ, Miyano T. Long-term postsurgical outcome of biliary atresia. J Pediatr Surg 1999:34(2):312-5. 5 Mowat AP, Davidson LL, Dick MC. Earlier identification of biliary atresia and hepatobiliary disease: selective screening in the third week of life. Arch Dis Child 1995:72:90-2. |
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M S Tanner, Professor of Paediatrics University of Sheffield
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Dear Sir Neonatal screening for MCADD Every baby born in the UK is screened for phenylketonuria and congenital hypothyroidism at 6 -14 days of age. Several screening laboratories now use tandem mass spectrometry (TMS) for the estimation of blood phenylalanine. TMS is capable of assaying simultaneously in the same sample a large number of other metabolites and thus potentially of detecting other metabolic disorders, including medium chain acyl-CoA dehydrogenase deficiency (MCADD). MCADD is almost as common as phenylketonuria, affecting approximately 1:15000 births in the UK. Infants with MCADD are well until challenged by a catabolic stress, most commonly a mild intercurrent infection and/or fasting. As a result of the acute encephalopathy affected infants may die or be left with profound neurological damage. Undiagnosed, MCADD has a mortality rate of up to 20% and 10-15% are left severely handicapped. However early treatment is simple, cheap and effective. Of 41 patients treated in 1 centre for a median of 6.7 years there were no additional deaths or appreciable mortality even though there was a high incidence of previous sibling death [1]. A possible concern about screening is the anxiety caused to parents whose MCADD infants never become ill because they are never challenged. However, it is indefensible to withhold from parents the knowledge that their child is at an easily avoided risk. It may be thought that we can rely upon clinical acuity to diagnose MCADD before severe damage occurs, but the non-specific features of the encephalopathy makes this an ineffective strategy. The extra cost of MCADD screening is less than £1 per baby . Two systematic reviews commissioned by the Health Technology Assessment (HTA) program in 1993 and published in 1997 [2,3] recommended further studies on the application of TMS to neonatal screening. In keeping with the ethos that all screening programmes should be evaluated, a moratorium on the introduction of screening for MCADD was agreed pending pilot studies. However the failure to fund those further studies has led to an impasse with very considerable frustration amongst all those involved. There is a risk that screening will be introduced without trials, as is already occuring in Bavaria, New South Wales, and parts of the USA. This will be a missed opportunity for a structured evaluation of this technology. Prevention is one of the challenges laid down in the National Plan for the NHS but the HTA process has failed the professionals, the children and their families. The challenge for us is how to move forward responsibly. 1. Wilson CJ, Champion MP, Collins JE, Clayton PT, Leonard JV. Outcome of medium chain acyl-CoA dehydrogenase deficiency after diagnosis. Arch Dis Child. 1999; 80:459-62. 2. Pollitt RJ, Green A, McCabe CJ, Booth A, Cooper NJ, Leonard JV et al. Neonatal screening for inborn errors of metabolism: cost, yield and outcome. Health Technol Assessment 1997;1: No. 7 ( http://www.hta.nhsweb.nhs.uk/) 3. Seymour CA, Thomason MJ, Chalmers RA, Addison MJ, Bain MD, Cockburn F et al. Neonatal screening for inborn errors of metabolism: a systematic review. Health Technol Assessment 1997;1: No. 11 ( http://www.hta.nhsweb.nhs.uk/) Stuart Tanner
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