STUDY OF VARIATION OF BGP CONCENTRATION - INFLUENCE OF SAMPLE COLLECTION, RADIOIMMUNOASSAY KITS AND NYCTHEMERAL RHYTHM

Osteocalcin or bone GLA protein (BGP) can be used as well as a periphe ral marker of the action of hormones on osteoblast. In the present stu dy, we report our clinical and biological results in three different c onditions: the kits used for determination, the time and the hour of w ithdrawal. We used 4 different radioimmunoassay kits: two kits (Elsa-o s-nat (cis), Osca-test (Henning)) detect intact osteocalcin molecules only and the two others (Elsa-osteo(cis), Ostk-PR(cis)) detect intact osteocalcin molecules and osteocalcin fragments. Time between collecti on and assay is important: we observed a diminution of osteocalcin lev el which can be due to the degradation of intact molecules, of 25% to 49% (depending on the kit used). The clinical profile was studied with circadian rhythm. We observed a variation of osteocalcin level in 30% of circadian rhythm according to the hour of collection sample. In co nclusion, we have seen two differents situations at risk of wrong inte rpretation due to low level BGP: inadequate serum collection or single blood collection instead of circadian cycle.