Methodological aspects on measurement of Clara cell protein in urine as a biomarker for airway toxicity, compared with serum levels.

The Clara cell protein CC16, secreted from Clara cells in the lung, is discussed as a potential biomarker for toxic effects on the airways. An increased concentration of CC16 in serum may be caused by increased permeability of the lungs, caused by high levels of air pollution. Since CC16 is eliminated by renal excretion, it may be possible to use urine instead of serum samples. Few studies have been conducted on urinary CC16 (U-CC16), however. The aim was to investigate the optimal way of sampling and quantifying CC16 in urine samples and compare CC16 in human serum and urinary samples. Repeated sampling was performed in two groups of healthy subjects. First morning urine, 24 h urine, and matched blood and urine samples were collected. The excretion of U-CC16 increased over the day, e.g. from 0.08 microg h(-1) in the morning to 0.28 microg h(-1) in daytime and 0.16 microg h(-1) in the evening (medians in males). Morning samples (microg h(-1)) from males properly reflected the 24 h excretion (r = 0.91). The best correlation with 24 h excretion was obtained with creatinine-corrected first morning urine samples (r > 0.9). Generally, females had lower excretion of CC16 than males (medians 2.5 microg 24 h(-1) in females and 16 microg 24 h(-1) in males). There was significant intraindividual variation, but the interindividual variation was larger in both groups. There was an association between serum CC16 (S-CC16) and U-CC16 in morning samples. With optimal methods for sampling U-CC16, urine samples may be used in experimental studies of air pollution. Copyright 2006 John Wiley & Sons, Ltd.