SUMMARY:Parathyroid hormone (PTH) and vitamin D [calcidiol or 25(OH)D] assays are used to diagnose chronic kidney disease-mineral bone disorder, and to guide and monitor interventions. Unfortunately, both assays have limitations. These limitations include analytical variability because of a lack of assay standardization, different calibrators used for each kit and differences in antibody specificity. For PTH assays, this leads to variability in the assessment of fragments and differences between results among kits from different manufacturers. For vitamin D, this leads to differences in the ability to detect D2 and D3 derivatives and differences among assays. For PTH, these problems are amplified by collection and handling differences and, for vitamin D, by diurnal and seasonal variation. Understanding these limitations should help clinicians to appropriately interpret results; attempts to develop universal standards to minimize these limitations may enhance the ability of these hormone measurements to predict underlying disease states.
KEY WORDS: assay, chronic kidney disease, mineral bone disease, parathyroid hormone, vitamin D.To detect biochemical abnormalities, healthcare practitioners rely on clinical laboratory tests and specific thresholds or acceptable ranges for such tests are often recommended by clinical practice guidelines. Unfortunately, such guidelines seldom contain information about the performance characteristics for key tests, nor measurement methodology or standards. However, understanding the limitations of assays is critical for appropriate clinical interpretation. In the management of chronic kidney disease-mineral bone disorder (CKD-MSD), diagnostic and therapeutic decisions are often made on the basis of the hormonal assays parathyroid hormone (PTH) and vitamin D. This review will discuss the limitations of these assays and the impact such limitations may have on CKD patient care.