Commentary: Active cascade screening for cystic fibrosis

BMJ 1994; 308 doi: (Published 04 June 1994) Cite this as: BMJ 1994;308:1468
  1. T Marteau
  1. Psychology and Genetics Research Group, United Medical and Dental Schools of Guy's and St Thomas's Hospitals, Ground Floor, Old Medical School Building, Guy's Campus, London SE1 9RT.

    Super and colleagues present the results of one of the first descriptive studies of cascade screening for carriers of cystic fibrosis, suggesting that this may be a useful approach to screening. But more needs to be known before accepting their recommendation for widespread application.

    To evaluate any service we must first define its objective. Several sets of guidelines have now been published in the United Kingdom on conducting genetic screening programmes.*RF 1-3* All these documents agree that the primary objective of screening is to provide information to allow people to make informed choices. Although a reduction in the number of births of infants with the disorder in question may occur as a result, such reductions are not a stated purpose of screening.

    Yet evaluations of screening programmes usually fail to assess the extent to which decisions about screening are based on good information. Super and colleagues' study of cascade screening is no exception. On the basis of a large uptake of carrier and prenatal testing they conclude that cascade screening - that is, actively seeking relatives of people with cystic fibrosis to invite them to have their carrier status determined should be widely implemented. But they have determined only the numbers of carriers who can be detected from a sample of patients and the termination rate of affected fetuses.

    If the primary objective of carrier testing is to provide information about reproductive options then many other questions need to be answered before implementation is considered. How good was the information provided before carrier testing and before prenatal diagnosis and subsequent termination? How well was this information understood? What was the quality of decision making about undergoing testing when in some cases the only contact with health professionals was just a letter? How did people understand negative test results, and were they reassured by them? What was the impact of learning about carrier status too late in pregnancy for prenatal tests? How were carrier couples counselled about their risks? What were the short and long term emotional outcomes for these parents? The authors' conclusion that cascade screening is more efficient than some other screening approaches cannot be inferred from an uncontrolled study in which key outcomes have not been assessed.

    Many commissioning authorities are understandably concerned with the economic consequences of their choices of which services to provide. The decision whether to purchase a particular screening programme may therefore depend largely on the numbers of carriers likely to be detected and the probability that any affected fetuses will be terminated. Those providing genetic screening services have the clinical responsibility of ensuring that any programmes offered for purchase are those for which there is evidence that decisions about testing and termination are well informed ones. Researchers, too, have a responsibility to frame their questions within existing professional guidelines. Failure to do so serves only to reinforce a crude and potentially dangerous cost-benefit approach to genetic screening, whereby people with genetic conditions are seen only as financially burdensome - a a burden that can be avoided by selective termination. Use of existing guidelines goes some way towards avoiding such dangers, protecting health professionals from accusations of eugenics. They should be used.


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