[Radioimmunoassay of urinary cotinine: variability of measurements, identification of exposed subjects].

Urinary cotinine was assessed by a radioimmune assay (RIA) in a random subsample of 63 (out of 285) children aged 5 to 6 from 10 kindergartens in Nancy (N-E France). The result was adjusted for urine concentration by expressing cotinine per mg creatinine. The correlation between two successive determinations was excellent (r = 0.989) and the difference between the two mean values was minimal and non-significant (121.4 +/- 25.9 vs 121.0 +/- 25.0). Expressed in percentage of their mean, the difference between two determinations was on average 8.2%. The urinary cotinine determinations allowed a satisfactory separation of children exposed vs unexposed to parental tobacco smoke.