Current parathyroid hormone immunoassays do not adequately meet the needs of patients with chronic kidney disease

Background: There are significant differences in plasma parathyroid hormone (PTH) results obtained by current immunoassay methods. However, many clinical guidelines relevant to patients with chronic kidney disease (CKD) that recommend PTH target values do not take account of these differences. This raises major questions about the validity of the evidence underpinning current use of PTH measurements in the management of CKD as well as of published relevant audit data. Methods: PTH was measured in plasma from patients with CKD in six commercially available immunoassays. The initial pilot study included 19 patients while 98 patients were included in a second extended study. Data from the second study were analysed by regression analysis to obtain assay-specific targets for each immunoassay. Results: Although similar PTH reference intervals are provided by most manufacturers, both studies confirmed substantial between-method differences in observed PTH for all patients, with results varying by as much as 4.2-fold between the lowest and highest reading methods. These differences were sufficient to have treatment implications for 79% of the patients in the pilot study. Applying the assay-specific targets derived here to results from the extended study decreased treatment misclassifications from 53% to 12%. Conclusions: Existing between-method differences in PTH measurements clearly have treatment implications. International initiatives to address these differences are in progress and will require support and input from all stakeholders. Adoption of assay-specific target values such as those reported here provides a convenient and practical interim solution that should lead to significant improvement in patient management, while also enabling meaningful audit.