Comparative study of urinary cotinine assayed by colorimetric semi-quantitative method and rapid test kit in passive-smoking pregnant women
This study aimed to evaluate the detection of urinary cotinine based on a semi-quantitative direct barbituric acid method (DBA) compared to immunochromatography method (COT). The intensity of color reaction of DBA method was divided into 4 levels,1+ to 4+,which corresponded to cotinine concentration of 10, 25, 50 and 100 mmol.L-1 respectively. The study was performed in 50 questionaired as second-hand smoking pregnant women.The results showed that DBA method gave 7 positive samples (14%) while 9 were detected as positive with COT method (18%). The two COT positive DBA negative samples had cotinine levels of 2.5 and 6.6 mmol.L-1. When compared to COT method, DBA semi-quantitative method was found to have a sensitivity of 78%, a specificity of 100%, a positive predictive value of 100% and a negative predictive value of 95%. The agreement of both methods were 74% and 100% for positive and negative results, respectively. The results indicated that DBA semi-quantitative is a reliable method, compared to COT, to test urinary cotinine in second-hand smoking pregnant women. However, low cotinine concentrations can result in fault negative or unclear reading. Thus DBA semi-quantitative method offers a less-time consuming, low cost method suitable for screening nicotine exposure in a large sample size.
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