Clinical evaluation of two novel biointact PTH(1–84) assays in hemodialysis patients

In chronic kidney disease–mineral and bone disorder (CKD-MBD), most treatment decisions are guided by parathyroid hormone (PTH) levels. Here, we aimed at assessing the technical and clinical performance of two novel automated biointact PTH(1–84) assays, from Roche Diagnostics (Ro) and DiaSorin (DS), in hemodialysis patients. We recorded demographics, dialysis treatment characteristics, pharmacotherapy for CKD-MBD and laboratory work-up. Statistical methods included Passing–Bablok, and multiple linear regression. 121 patients, dialyzing on average for 3.5years (range: 0.1–22.5), with serum phosphate 1.9±0.6mmol/L (mean±SD), participated in the study. Median serum concentration for intact PTH was 223ng/L (range: 5–2844), and for biointact PTH(1–84) was 136ng/L (Ro; range: 1–1644), respectively 138ng/L (DS; range: 4-1580). Both biointact assays were significantly correlated (r=0.98; Ro=0.87×DS+19.60). Bland–Altmann plots revealed an average bias ±2 SD of 10±27ng/L below 200ng/L, and −32±157ng/L above 200ng/L (Ro minus DS). The variably adjusted association between PTH and serum phosphate was very similar, regardless of the PTH assay, but this was not the case for PTH-derived measures (ratios biointact/intact; differences intact minus biointact). (Log)PTH concentrations as well as serum phosphate were significantly associated with serum creatinine, but only in patients with >0mL urine per day. Results from Roche and DiaSorin biointact PTH(1–84) assays were well correlated, but showed increased deviations at higher concentrations. Biointact PTH(1–84) levels are roughly two third of intact PTH. The association between PTH and serum creatinine may depend on residual renal clearance of PTH and/or serum phosphate. ► We compared “intact PTH” with “biointact” PTH(1–84) (assays from 2 suppliers). ► The results from both biointact PTH(1–84) assays correlated very well. ► The assays should not be used interchangeably, as indicated by Bland-Altmann plots. ► Biointact PTH(1–84) levels are roughly two third of intact PTH. ► Serum creatinine associated positively with PTH in patients with >0ml urine/day.