Inter-method variability in PTH measurement: Implication for the care of CKD patients

• Published in: Kidney international Vol. 70; no. 2; pp. 345 - 350
• Main Authors: Souberbielle, J.-C., Boutten, A., Carlier, M.-C., Chevenne, D., Coumaros, G., Lawson-Body, E., Massart, C., Monge, M., Myara, J., Parent, X., Plouvier, E., Houillier, P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-07-2006; Elsevier Limited
• Subjects: Adult; Antibody Specificity; assay standardization; Chemistry, Clinical - standards; chronic kidney disease; Chronic Kidney Disease-Mineral and Bone Disorder - blood; Chronic Kidney Disease-Mineral and Bone Disorder - diagnosis; Evaluation Studies as Topic; Humans; immunoassay; Immunoassay - standards; Kidney Failure, Chronic - blood; Kidney Failure, Chronic - diagnosis; NKF/K-DOQI; parathyroid hormone; Parathyroid Hormone - analysis; Parathyroid Hormone - blood; Parathyroid Hormone - chemical synthesis; Peptide Fragments - analysis; Peptide Fragments - chemical synthesis; Reference Standards; Reproducibility of Results; parathyroid hormone; chronic kidney disease; NKF/K-DOQI; antibody specificity; assay standardization; immunoassay
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1038/sj.ki.5001606

The National Kidney Foundation/Kidney-Dialysis Outcome Quality Initiative guidelines recommend to maintain the serum intact parathyroid hormone (PTH) concentration between 150 and 300 ng/l in chronic kidney disease (CKD) stage 5 patients. As these limits were derived from studies that used the Allegro intact PTH assay, we aimed to evaluate whether they were applicable to other PTH assays. We compared the PTH concentrations measured with 15 commercial immunoassays in 47 serum pools from dialysis patients, using the Allegro intact PTH assay as the reference. We also evaluated the recovery of graded amounts of synthetic 1–84 and 7–84 PTH added separately to a serum pool. Although the assays were highly correlated, the concentrations differed from one assay to another. The median bias between the tested assays and the Allegro intact PTH assay ranged from -44.9 to 123.0%. When the PTH concentrations were 150 or 300 ng/l with the Allegro intact PTH assay, they ranged with other assays from 83 to 323 ng/l and from 160 to 638 ng/l, respectively. The tested assays recognized 7–84 PTH with various cross-reactivities, whereas a given amount of 1–84 PTH was recovered differently by these assays. We found important inter-method variability in PTH results owing to both antibody specificity and standardization reasons. The unacceptable consequence is that opposite therapeutic attitudes may be reached in a single patient depending on the PTH assay used. We propose to use assay-specific decision limits for CKD patients, or to apply a correcting factor to the PTH results obtained with a given assay.