PTH Blood Test Found Unreliable

A widely used assay for parathyroid hormone (PTH) has been found to be both inappropriate and potentially harmful to patients when used with established guidelines for end-stage renal disease, according to new research.

The blood test measures levels of the parathyroid hormone, produced in the parathyroid gland. The results help doctors diagnose conditions such as hyperparathyroidism or determine the causes of abnormal regulation of calcium by the bones of patients with renal disease, which may lead to arterial calcification. Too high or too low levels of PTH can affect calcium metabolism and bone integrity, and can cause vascular disease.

Guidelines developed in 2003 by the U.S. National Kidney Foundation for the diagnosis and treatment of kidney disease are based on the use the of a manual iPTH assay that is not used much for routine clinical analysis. Many nephrologists have shifted to the use of another assay that generates much different results. Almost all U.S. testing of dialysis patient specimens is performed in one of seven centralized labs. None of these use the PTH test on which the bone metabolism guidelines are based.

As a result, it appears that rates of parathyroidectomy may have been increased, patients have been over-treated with expensive medications, and adynamic bone disease has become more prevalent, now affecting half of all dialysis patients.

These changes were tracked by Tom Cantor, B.Sc., president and CEO of Scantibodies Laboratory, Inc. (SLI, Santee, CA, USA), and his research team. His editorial on these changes appeared in the November 29, 2005, issue of the journal Seminars in Dialysis. In the editorial, he noted that "careful attention to the comparability of PTH assays is required by nephrologists and those who serve patients in this area.” His team has developed a more-specific assay for PTH.





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