Clinicians worried about bone disease developing in patients with chronic kidney disease (CKD) lean on parathyroid hormone (PTH) measurements as a marker for skeletal and mineral disorders. But the utility of PTH assays is controversial—mainly because the variability among analytical techniques makes the interpretation of results difficult.
A working group from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) is working to standardize the assays and establish protocols for issues such as pre-analytical variables. The group has the support of many stakeholders, including testing manufacturers, and expects to show progress within the next couple of years. In the meantime, nephrologists can consult the literature to aid in the interpretation of the assays used by their laboratories.
“There can be differences up to fourfold in the results reported with different methods from the same samples,” said the chair of the IFCC group, Catherine M. Sturgeon, PhD, who is consultant clinical scientist at the Royal Infirmary of Edinburgh and director of one of the National External Quality Assessment Service proficiency testing centers in the U.K. “The bigger and more complicated a molecule is, the more difficult it can be to measure consistently.”
PTH is one of those complicated molecules. It is an 84-amino-acid peptide protein that breaks down in the body into a large variety of peptide fragments. The fragments are generally considered not biologically active, although there is some controversy about how active some might be.