November 29, 2005
Dialysis patients may be overmedicated due to unreliable blood test
Changes in a widely used assay (blood test) for parathyroid hormone (PTH) have made its use with the established guidelines for end stage renal disease clinical management both inappropriate and potentially harmful to patients. This research is published in the journal Seminars in Dialysis.
A PTH assay measures levels of parathyroid hormone, produced by the parathyroid gland, which helps diagnose conditions such as hyperparathyroidism or to determine causes of abnormal regulation of calcium by the bones of patients with renal disease, which can lead to arterial calcification. Levels of PTH that are too high or too low can affect calcium metabolism, bone integrity and cause vascular disease.In 2003, the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (K/DOQI) published the Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease. These guidelines, for both diagnoses and treatments, are based on use of a manual iPTH assay that is not widely used for routine clinical analysis.
According to an editorial in Seminars in Dialysis, the iPTH assay that is now widely used by nephrologists has shifted significantly compared to the assay on which K/DOQI guidelines are based, generating much different results. Currently, almost all testing of dialysis patient specimens in the United States are performed at one of seven centralized labs. None use the PTH test on which the K/DOQI bone metabolism guidelines are based.
As a result, evidence shows 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 dialysis patients.
Tom Cantor, author of the editorial, and his research team have tracked changes in the most commonly used PTH assay. The team has also developed a more specific assay for PTH.
They have found important inconsistencies in testing results, Cantor states, indicating that "careful attention to the comparability of PTH assays is required by nephrologists and those who serve [patients] in this area."
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