Abstract

Serum β-crosslaps are an established laboratory test to investigate bone metabolism. However, lytic conditions may affect the measurement of serum β-crosslaps. Therefore, we investigated the effect of cathepsin C and human leukocyte lysate on serum β-crosslaps in relation to temperature and time. We divided eight serum samples with elevated β-crosslaps levels into three aliquots and stored them at 4, 21 and 37°C. Another five serum samples were divided into three aliquots and adjusted to contain different cathepsin C concentrations (50, 250, 500 IU/l). These aliquots were divided again and stored at 4, 21 and 37°C. Finally, three aliquots from three additional serum samples were treated with human leukocyte lysate (100, 300, 500 IU/I), divided again and stored at 4, 21 and 37°C. Measurements of serum β-crosslaps were then carried out before and immediately after manipulation, and after 2 and 5 days of storage. When stored at 21°C, serum β-crosslaps diminished significantly (25% after 5 days), but no significant change was detectable when they were stored at 4°C. Cathepsin C induced up to a 14% increase in β-crosslaps while human leukocyte lysate caused up to a 17% decrease.

This study demonstrates that the influence of proteolytic conditions on the serum concentration of β-crosslaps is not uniform. Leukocyte lysate decreased serum β-crosslaps while the addition of cathepsin C increased their concentration. Therefore, serum should be separated from the whole blood immediately after coagulation and stored until analysis in a deep freezer.