An automated colorimetric assay for urine nicotine metabolites: a suitable alternative to cotinine assays for the assessment of smoking status.

We have modified the direct barbituric acid (DBA) test for urine nicotine metabolites so that it can be used on a continuous flow auto-analyser. The performance of the method was compared with a cotinine radio-immunoassay (RIA). The auto-analyser DBA method and cotinine RIA performed equally well in terms of assessing smoking status, yielding a false positive rate of 1.5% at a detection rate of 98% when compared to self-reported smoking information. The results obtained with the two methods were correlated, r = 0.91, although the DBA method results were consistently higher than the corresponding cotinine RIA results; the method detects cotinine and other nicotine metabolites. The coefficient of variation for the DBA method was 3.4% compared with 10% for the RIA. The DBA method has a throughput of about 250 samples per day compared to about 70 per day by RIA and the reagents are readily obtained and inexpensive.