Background: Measurement of procollagen type I N-terminal propeptide (PINP) concentration in serum reflects the rate of type I collagen synthesis and can therefore be used as a bone formation marker. There are two methods of PINP quantification; the first measures the trimeric propeptide (intact PINP) and the second measures both the trimeric and monomeric propeptides (total PINP). Trimeric PINP is excreted via hepatic endothelial cells whereas monomeric PINP is cleared renally. Therefore in renal failure the total assay has a positive bias with respect to the intact assay, due to monomeric PINP accumulation. The aim of this study was to compare the performance of both assays across all stages of chronic kidney disease (CKD).

Methods: Serum was taken from male (n=111) and female (n=105) patients attending a metabolic bone clinic and these were partitioned into stages of CKD 1-5. Each serum sample was analysed using the Roche electrochemiluminescence immunoassay for total PINP and the Immunodiagnostic Systems chemiluminescence immunoassay for intact PINP.

Results: Passing-Bablok regression analysis comparing both methods showed that with advancing CKD there was a proportional positive bias affecting the total assay when compared to the intact assay. This proportional positive bias was statistically significant for CKD stages 3b, 4 and 5.

Conclusions: Based on this method comparison study, usage of the total PINP assay should be avoided in CKD stages 3b, 4 & 5 (eGFR <u><</u>44 ml/min/1.73m²) and instead an intact assay used as the total assay overestimates PINP levels due to monomeric PINP accumulation.

背景：血清中 I 型前胶原 N 端前肽 (PINP) 浓度的测量反映了 I 型胶原合成的速率，因此可用作骨形成标志物。PINP 量化有两种方法；第一个测量三聚体前肽（完整的 PINP），第二个测量三聚体和单体前肽（总 PINP）。三聚体 PINP 通过肝内皮细胞排泄，而单体 PINP 则通过肾脏清除。因此，在肾功能衰竭中，由于单体 PINP 积累，总检测相对于完整检测具有正偏差。本研究的目的是比较两种检测在慢性肾病 (CKD) 各个阶段的性能。

方法：从参加代谢骨诊所的男性 (n=111) 和女性 (n=105) 患者中提取血清，并将这些患者分为 CKD 1-5 期。使用 Roche 电化学发光免疫分析法分析每个血清样品的总 PINP 和免疫诊断系统化学发光免疫分析法分析完整的 PINP。

结果：通过比较两种方法的 Passing-Bablok 回归分析表明，与完整测定相比，随着 CKD 的进展，存在影响总测定的成比例的正偏差。对于 CKD 3b、4 和 5 期，这种比例正偏差具有统计学意义。

结论：基于该方法比较研究，在 CKD 3b、4 和 5 期应避免使用总 PINP 检测（eGFR <u><</u>44 ml/min/1.73m<sup>2</sup >) 而作为总检测的完整检测由于单体 PINP 积累而高估了 PINP 水平。