Clinical guidelines and PTH measurement: does assay generation matter?

Abstract

Parathyroid hormone (PTH) is an important regulator of calcium and phosphate homeostasis and bone remodeling. PTH is metabolized into PTH fragments which are measured to a different extent by PTH assays of different generations. This is due to differences in fragments recognized and lack of assay standardization. PTH is measured in the workup of several conditions and clinical guidelines provide recommendations concerning these measurements. This review provides an overview of the impact of differences between PTH assays, when applying distinct clinical guidelines for primary and secondary hyperparathyroidism and perioperative use of PTH measurements. Guidelines deal with PTH measurement in different ways, recommending either trend monitoring, the use of a fold-increase of the upper reference limit, or state an absolute PTH cut-off value. For classic primary hyperparathyroidism (PHPT) the type of PTH assay used will not affect diagnosis or management as the precise concentration of PTH is less relevant. In chronic kidney disease (CKD), the guideline recommends treatment of secondary hyperparathyroidism (SHPT) above a 2-9-fold PTH increase, which will result in different clinical decisions, dependent on the assay used. For patients after bariatric surgery guidelines state absolute cut-off values for PTH, however, the impact of different generation assays is unknown as direct comparison of PTH assays has never been performed. During parathyroid surgery, PTH measurements with a third generation assay reflect treatment success more rapidly compared to second generation assays. Increased awareness among clinicians regarding the complexity of PTH measurements is warranted, as it potentially affects clinical decisions.