Validation of urinary thiocyanate as a biomarker of tobacco smoking

Thiocyanate ion (SCN) is the major detoxication product of cyanide, which is converted to SCN by a thiosulphate sulphurtransferase, mainly in hepatic mitochondria. Low-level cyanide exposure for man is caused by factors such as dietary intake of cyanogenic glucosides, tobacco smoking, drug administration and occupational exposure to organic nitriles. Urinary SCN concentration was determined through a commercial kit for the analysis of cyanide in water. Spot urine samples were collected at 7:30 h and 12:30 h, from 99 healthy male white-collar office workers (non-smokers n=72, smokers n=27). Comparison of SCN excretion values did not show any difference between the morning and midday samples. The SCN median value of non-smokers was 24 μmol l(-1) (range 9-24 μmol l(-1)) and was statistically different from that of smokers (SCN = 92 μmol l(-1), range 33-275 μmol l(-1)) (p<0.001). In smokers median levels of SCN increased with the intensity of tobacco smoking and SCN individual excretion rose in relation to the number of cigarettes smoked daily (r=0.78, p<0.0001, n=16). In the whole group of investigated subjects SCN excretion was correlated with urinary cotinine, a well know biomarker of tobacco consumption (r=0.86, p<0.001, n=99). When the assay was applied as a smoking habit screening test, with a cut-off value of SCN=38 μmol l(-1) adopted to discriminate between non-smokers and smokers, the following smoker track-down predictive values resulted: 93% negative for non-smokers and 96% positive for smokers.