Plasma YKL-40 levels in healthy subjects from the general population.

BACKGROUND

Plasma YKL-40 is a new biomarker in patients with cancer and inflammatory diseases. High plasma YKL-40 is associated with poor prognosis. Our aim was to determine reference levels in healthy subjects.

METHODS

Plasma YKL-40 was determined in 3130 participants aged 20-80 years from the Danish general population, the Copenhagen City Heart Study. They had no known disease at time of blood sampling in 1991-1994 and remained healthy and alive during a 16-year follow-up period. In 644 participants, YKL-40 was measured again in samples taken 10 years after the first.

RESULTS

The median plasma YKL-40 was 40 μg/L (2.5-97.5% reference levels: 14-155) with no difference between sexes. YKL-40 increased exponentially with age. For age-adjusted reference levels, the YKL-40 percentile as a function of age in years and plasma YKL-40 in μg/L was derived: percentile=100/(1+(YKL-40^-3)*(1.062^age)*5000). In subjects with two YKL-40 measurements 10 years apart, the mean increase in YKL-40 was 1.5 μg/L/year (SE: 0.2), while the mean change in the calculated age percentile was minimal (-0.3; SE: 0.1).

CONCLUSIONS

Plasma YKL-40 increases with age within and across healthy individuals from the general population. Age-stratified or age-adjusted reference levels are important when YKL-40 test results are evaluated.