Procollagen III, N-terminal propeptide (PIIINP) is used as a biomarker for increased collagen III-synthesis. Reference intervals have not been established for the MAGLUMI 800 chemiluminescence immunoassay (CLIA) in Northern European adults or in children. The present study aimed to establish age-specific reference intervals in a Northern European population. PIIINP serum levels were analysed in healthy blood donors 19-67 years (n = 240) and children 2-18 years (n = 420). Furthermore, we investigated total imprecision and stability at room temperature and at -20 °C and performed a method comparison between MAGLUMI 800 CLIA (Snibe Diagnostics, Shenzhen, China) and ADVIA Centaur CP (Siemens Healthcare Diagnostics, Tarrytown, NY,USA). PIIINP was influenced by age but not sex. We established the following reference intervals: 2-10 years, 18-62 µg/L; 11-18 years, 15-75 µg/L; 19-39 years, 15-55 µg/L; 40-67 years, 14-31 µg/L. Total imprecision for PIIINP on MAGLUMI 800 was acceptable with coefficients of variation of 4.9% in the low range and 9.4% in the high range. PIIINP was stable for 24 h at room temperature after centrifugation and for at least 7 months at -20 °C. MAGLUMI 800 yielded significantly higher PIIINP levels than ADVIA Centaur CP. In conclusion, we established age-specific reference intervals for PIIINP using MAGLUMI 800 CLIA in a large Danish cohort. Our results may be useful for other laboratories wishing to establish PIIINP on the same platform and may provide improved guidance for medical doctors treating both children and adults with fibrotic disorders.
Keywords: N-terminal propeptide; Procollagen III; assay precision; assay validation; liver fibrosis; method comparison; reference interval; systemic sclerosis.