A Method Comparison of the Roche Intact PTH Method versus the Roche Whole PTH (1-84) Method: Examining the Differences Based on eGFR

Aim: Third-generation whole PTH (1-84) parathyroid hormone (PTH) assays do not recognize the PTH 7–84 fragment whereas second generation (intact) assays detect both 1–84 and 7–84 PTH fragments. This study aimed to compare the second-generation Roche intact PTH method with the third-generation Roche whole PTH (1-84) method, examining differences based on estimated glomerular filtration rate (eGFR). Methods: The intact PTH method and whole PTH (1-84) method were compared using 100 serum samples selected across eGFR quintiles for chronic kidney disease (CKD) stages 1 to 5 in accordance with Kidney Disease: Improving Global Outcomes (KDIGO). Results: Method comparison based on eGFR showed that differences between both PTH methods were not significant at eGFR >60 ml/min/1.73m2. There was a statistically significant difference at eGFR <60 ml/min/1.73m2. The whole PTH (1-84) method produced lower results as eGFR decreased: CKD Stage 3 (mean difference: -21%; 95% confidence interval: -16 to -26%) to CKD Stage 5 (mean difference: -46%; 95% confidence interval: -40 to -52%). Conclusions: Differences observed between the two assays may be due to second-generation PTH assays overestimating PTH concentration by measuring both 1-84 PTH and C-terminal fragments, notably PTH (7-84) in patients with significant renal impairment. The whole PTH (1-84) assay may be reflexed to use as a tool to monitor metabolic bone disease risk. Initial dual reporting of PTH by both methods is recommended for eGFR <60 ml/min to educate users due to the difference in results.