Parathyroid hormone assay drift: an unappreciated problem in dialysis patient management.

The Kidney Disease Outcomes Quality Initiative (K/DOQI) bone metabolism guidelines assume that clinicians use the Nichols intact parathyroid hormone immunoradiometric assay (iPTH IRMA) upon which K/DOQI was based. But for more than a decade, virtually all PTH assay results used for routine end-stage renal disease (ESRD) clinical management have not been generated with this test. Results from the most widely used PTH assays for ESRD patient testing in the United States have varied from 1999 to 2005. The Nichols chemiluminescent Advantage iPTH assay results shifted upwards significantly in 1999 and remained elevated until 2005. From 2003 to 2005, results from the Nichols Advantage Bio-Intact PTH assay shifted upward on average by 29% to 52%. These changes in the most widely used PTH assays have made use of the K/DOQI guidelines with these assays both inappropriate and potentially harmful to patients.