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Background: Aminoterminal propeptide of type I procollagen (PINP) reflects bone formation. Two different antigens exist in human serum: intact PINP and a monomeric form. The intact PINP assay measures trimeric form and the total assay measures both forms. The structure and origin of the monomeric form is still unclear., Methods: Automated intact and total PINP assays were compared in breast cancer patients with (n = 60) or without bone metastases (n = 226). In addition, cross-linked carboxyterminal telopeptide of type I collagen (ICTP) was measured from the same patients and compared with the concentration of PINP monomer (difference between intact and total PINP). Monomeric PINP was purified from human ascitic fluid and characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)., Results: The correlations were good (r > 0.948) between intact PINP and total P1NP in all patient groups. The correlation between the monomeric form and ICTP was lower in patients without bone metastases (r = 0.507) than in patients with bone metastases (r = 0.894). This indicates that the monomeric form reflects the degradation of type I collagen because bone metastases are osteolytic in nature. After several steps in the purification of the monomer form there was a single peak. Only the single band was visible in the SDS-PAGE gel. The alpha1-chain of intact PINP consists of 161 amino acids with a molecular weight of 14224.02. The purified monomer peptide in MALDI-TOF MS was smaller, 10576.41, and most likely cleaved after the arginine residue (amino acid number 120) with a trypsin-like protease., Conclusions: Intact and total PINP assays give similar results in many conditions, but there are differences, for example in breast carcinoma, which should be recognized.

Background: The concentration of N-terminal propeptide of type I procollagen (PINP) in the serum reflects the rate of type I collagen formation. Intact PINP assay measures the trimeric propeptide while total P1NP assay measures both trimeric and monomeric forms. In this study we compared these two assays emphasizing the possible differences., Methods: Intact and total PINP were measured from serum in healthy Finnish blood donors (n = 34) and in the patients with chronic renal failure before and after haemodialysis (n = 39). In addition, the serum of a normal man, pooled hospital serum samples and the serum of a patient with haemodialysis treatment were fractioned by gel filtration and trimeric and monomeric forms were located. Fractions were lyophilized and intact and total PINP were measured in each fraction. Samples from bedridden geriatric patients (n = 173) were also measured using intact and total PINP assays and a degradation marker of type I collagen (ICTP)., Results: The correlation between intact and total PINP in controls was 0.89 and their PINP concentrations were similar. In haemodialysis or bedridden geriatric patients, the PINP methods gave significantly different results. In gel filtration studies, intact PINP hardly measured monomeric form even if its concentration was disproportionately increased in haemodialysis patients. In bedridden geriatric patients, the difference of total and intact PINP correlated significantly to degradation marker ICTP., Conclusions: Difference between total and intact assays for PINP seem to reflect degradation of pN-collagen rather than denaturation of intact propeptide.

Background: The stability of analyte concentrations in plasma after prolonged contact with blood cells in uncentrifuged lithium-heparin gel tubes was studied., Methods: To investigate the stability of concentrations of 26 chemistry and 15 immunochemistry analytes, the simultaneously drawn samples (n = 50) were measured after 6 h storage at +8 degrees C and +22 degrees C in whole blood and after immediate separation of plasma. The analyte concentrations were measured with a Roche Modular PPEE analyser using reagents from Roche Diagnostics., Results: After prolonged contact with cells a clinically significant change was only observed for potassium where the mean value increased from 4.0 mmol/L to 4.8 mmol/L (P < 0.001) when stored at +8 degrees C., Conclusion: Immediate separation of plasma from cells is recommended. However, when prolonged contact of plasma with cell is unavoidable, samples can be kept uncentrifuged for up to 6 h at +8 degrees C or at +22 degrees C. The stability of potassium, however, is temperature-dependent and cannot be measured from refrigerated blood samples.