B-171 Comparison of Intact PTH and PTH Assays using LC-MS/MS Among Non-Dialysis Dependent Chronic Kidney Disease Patients

Abstract

Abstract Background Parathyroid hormone (PTH) is an important regulator of calcium and phosphate homeostasis and bone remodeling. It is metabolized into PTH fragments, which are measured to a different extent by PTH assays of different generations because of differences in fragments recognized and lack of assay standardization. Therefore, we developed an LC-MS/MS method for 1-84 PTH and aimed to compare with immunoassay among patients with chronic kidney disease (CKD) stages 3 to 5 not yet on dialysis. Methods Blood samples were collected from 252 patients with CKD stages 3 to 5. PTH concentrations were measured simultaneously by using the second-generation—PTH intact and immunocapture in situ digestion LC-MS/MS spectrometry assays. The severity of the kidney disease was based on the eGFR calculated by using the Modification of Diet in Renal Disease (MDRD) formula. Results Serum 1-84 PTH concentrations were strongly correlated but significantly lower than the intact PTH concentrations (r = 0.956, P < 0.0001). This finding was consistent among CKD stages 3 to 5. PTH concentrations by both assays (intact and 1-84 PTH) positively correlated with BUN (r = 0.613, r = 0.61; P < 0.0001, respectively), phosphorus (r = 0.423, r = 0.427; P < 0.0001, respectively) and negatively correlated with blood calcium (r = −0.355, r = −0.421; P < 0.0001, respectively), protein (r = −0.289, r = −0.305; respectively, P < 0.0001) and the estimated glomerular filtration rate (r = −0.468, r = −0.485; P < 0.0001, respectively). Conclusion Among patients with CKD stages 3 to 5 not on dialysis, the 1-84 PTH assay detected significantly lower PTH concentrations compared with intact PTH assay. This LC-MS/MS method can provide accurate and precise PTH results in patients with severe chronic renal failure. Additional studies that correlate the diagnosis and management of CKD mineral and bone disorders are needed to determine whether 1-84 PTH assay results are better surrogate markers in these early stages of CKD.