Comparison of 12 assays for detecting hCG and related molecules in urine samples from Down syndrome pregnancies

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Abstract
Urine is a new medium for Down syndrome testing. In an effort to determine the best type of human chorionic gonadotropin (hCG)‐related immunoassay for urine testing, we examined 14 Down syndrome and 91 unaffected pregnancy urine samples with 12 established assays. The assays included (a) those that detect hCG β‐core fragment only; (b) those that detect β‐core fragment with less than 18 per cent free β‐subunit cross‐reactivity; (c) that which equally detects free β‐subunit and β‐core fragment; and (d) those that detect hCG, free β‐subunit, or combinations thereof. The seven type a and b assays had the highest sensitivity for Down syndrome. The median MOM for Down syndrome was 5·93 (range 4·73–7·53). At a 10 per cent false‐positive rate, the median observed detection rate was 93 per cent (range 79–100 per cent) and the median predicted detection rate was 85 per cent (range 69–96 per cent). The assays that did not mainly detect β‐core fragment (types c and d) had poorer screening performance. The median MOM for Down syndrome was 2·70 (range 2·16–3·63 MOM). At a 10 per cent false‐positive rate, the median observed detection rate was 50 per cent (range 36–64 per cent) and the median predicted detection rate was 37 per cent (range 21–62 per cent). We infer that the assays that only detect β‐core fragment, or β‐core fragment with minor free β‐subunit cross‐reactivity (types a and b), are the better urine‐based tests for Down syndrome screening. © 1997 by John Wiley & Sons, Ltd.