The Significance of Urinary Hydroxyproline Excretion in Smokers and Passive Smokers

Summary

The urinary hydroxyproline/creatinine ratio was reported to be increased after smoking, passive smoking and exposure to ambient air polluted with nitrogen dioxide. In two field studies we tried to verify the results obtained in smokers. A weak positive association was found between the hydroxyproline/creatinine ratio and cigarette consumption for male smokers. In contrast, the amount of hydroxyproline excreted in the 24-h urine was not increased in male and female smokers as compared to their non-smoking counterparts. Standardizing the data for body surface led to the same results. From the findings obtained in smokers we conclude that passive smoking does not lead to an elevation of hydroxyproline excretion either.

In addition, we measured lower amounts of creatinine excreted in the 24-h urine of male, but not female smokers and higher 24-h urine volumes in smokers of both sexes as compared with non-smokers. Whereas an inverse correlation was found between the extent of smoking and the excretion of creatinine, the association between the extent of smoking and urinary volume was positive. Both findings acting together may explain the increased hydroxyproline/creatinine ratio as seen in smokers. Therefore the hydroxyproline/creatinine ratio is not a measure of the hydroxyproline excretion in smokers, nor is its determination an appropriate method of detecting lung damaging effects due to smoking and passive smoking.