Validation of an automated intact N-terminal propeptide of type I procollagen (PINP) assay

ObjectivesN-terminal propeptide of type I procollagen assay (PINP) reflects the rate of type I collagen synthesisDesign and methodsDifferent sera were fractioned by gel filtration and analyzed with intact and total PINP assays. The sizes of the antigens were determined by western blotting. The thermal stability was tested at + 37 °C, + 4 °C and room temperature (RT).ResultsAutomated intact PINP assay hardly measured monomeric form. In haemodialysis patients intact and total PINP assays gave significantly different results. The monomeric PINP antigen in serum was larger than the trimeric PINP antigen. PINP were thermally stable at least 7 days at + 4 °C and at RT but the results of both assays were decreased similarly at + 37 °C.ConclusionsThe IDS-iSYS intact PINP assay is precise and sensitive. It seems that monomeric form is not derived from the thermal instability of the trimers but acts as a confounding factor.