THE AMINOTERMINAL PROPEPTIDE OF TYPE-I PROCOLLAGEN - EVALUATION OF A COMMERCIAL RADIOIMMUNOASSAY KIT AND VALUES IN HEALTHY-SUBJECTS

Objectives: Evaluation of the performance of a radioimmunoassay kit fo r measuring serum concentrations of the aminoterminal extension peptid e of human type I procollagen, S-PINP. Design and Methods: S-PINP conc entrations in 229 healthy subjects, 140 females, aged 3.8-81 years, an d 89 males, aged 0.9-71 years, were measured with the kit. Because PIN P and PICP (the carboxy-terminal propeptide of type I procollagen) are formed in equimolar concentrations, we also calculated the PICP/PINP ratio and compared the S-PINP values to those of S-PICP, which have be en shown to correlate with bone formation rate. Results: The sensitivi ty of the assay was 2.3 mu g/L, the spiking recovery ranged from 95.5 to 100.3%, the dilution recovery from 79.3 to 103.1%. The intra-assay imprecision was 2.3 to 3.5% (CV), the interassay imprecision within on e reagent lot 2.5-5.2% and, between several reagent lots, 2.7 to 6.1% (CV). S-PINP in females over 20 years old ranged from 12 to 90 mu g/L (x = 39.7, SD = 14.7), in males over 25 years old, from 22 to 89 mu g/ L (x = 49.9, SD = 15.8); the PICP/PINP ratio ranged from 1.5 to 5.2 an d from 1.8 to 4.9, respectively. In females under 20 years old, S-PINP ranged from 52 to 820 mu g/L, in males aged 25 years or younger from 35 to 1404 mu g/L; the PICP/PINP ratio was 0.44-2.3 and 0.38-2.8. In f emales under 20 years and males under 25 years, there was a significan t negative correlation between S-PINP and age: r = -0.70, p < 0.001 fo r females, r = -0.52, p = 0.004 for males. In different groups of heal thy subjects, the correlation of S-PINP and S-PICP was significant (r = 0.67-0.86, p < 0.001). Conclusion: The assay performance is good. Th e significant positive relationship between S-PINP and s-PICP suggests that S-PINP also reflects bone formation rate. Because the clearance of PINP is probably less sensitive to hormonal changes, PINP may prove to be superior to PICP as a marker of bone formation.