A Novel High-Throughput Immunoaffinity LC-MS/MS Assay for P-III-NP and Other Fragments of Type III Procollagen in Human Serum

The amino-terminal propeptide of type III procollagen (P-III-NP) is used with IGF-I to detect the illicit use of growth hormone and to monitor growth hormone therapy. However, the only currently available assays for P-III-NP are immunoassays, which are not well harmonized. In addition, other fragments of type III procollagen may better evaluate collagen turnover. We aimed to develop a high-throughput assay using immunoaffinity enrichment coupled to ultra-high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantify peptides belonging to three different regions of type III procollagen in human serum simultaneously. To facilitate higher throughput, we transferred the assay from microcentrifuge tubes to a 96-well plate format with partially automated pipetting. The method was linear (Pearson's R ≥ 0.994) over an estimated concentration range of 1.35-13.3 nM, 0.04-2.28 nM, and 0.26-5.1 nM for each surrogate peptide of P-III-NP, collagen degradation products, and the carboxyl-terminal propeptide, respectively. Intra-day and inter-day imprecision were both