Letter

Testing should be in all women

BMJ 1995; 311 doi: 10.1136/bmj.311.7016.1372a (Published 18 November 1995)
Cite this as: BMJ 1995;311:1372.2

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  1. Nicholas J Wald,
  2. Anne Kennard,
  3. Hilary Watt,
  4. James E Haddow,
  5. Glenn E Palomaki,
  6. George J Knight,
  7. Jacob A Canick
  1. Professor Lecturer Statistician Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, Medical College of St Bartholomew's Hospital, London EC1M 6BQ
  2. Medical director Director of biometry Laboratory director Foundation for Blood Research, PO Box 190, Scarborough, ME 04074, USA
  3. Professor Department of Pathology and Laboratory Medicine, Women and Infants Hospital of Rhode Island, Providence, RI 02905, USA

    EDITOR,--The paper by J Fletcher and colleagues1 was incorrect to conclude that restricting serum screening for Down's syndrome to women aged 30 or over is preferable to screening all women. Firstly, using a 58% detection rate and a 5% false positive rate for all pregnant women instead of estimates applicable to women aged 30 or over (72% and 12%2 3), and, secondly, not comparing screening policies appropriately introduces important errors.

    Screening tests involve a trade off between detection rate and false positive rate. To compare screening policies, cut off levels must be set such that among all pregnancies in …

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