Chemical Characterization and Quantification of Circulating Intact PTH and PTH Fragments by High-Resolution Mass Spectrometry in Chronic Renal Failure.

Abstract

BACKGROUND:The precise concentrations of full-length parathyroid hormone (PTH1–84) and the identity and concentrations of PTH fragments in patients with various stages of chronic renal failure are unknown.METHODS:We developed a liquid chromatography-high resolution mass spectrometry (LC-HRMS) method to characterize and quantify PTH1–84 and PTH fragments in serum of 221 patients with progressive renal dysfunction. Following capture by matrix-bound amino-terminal or carboxyl-terminal region-specific antibodies and elution from matrix, PTH1–84 and PTH fragments were identified and quantitated using LC-HRMS. PTH was simultaneously measured using an intact PTH (iPTH) immunoassay.RESULTS:Full-length PTH1–84 and 8 PTH fragments (PTH28–84, 34–77, 34–84, 37–77, 37–84, 38–77, 38–84, and 45–84) were unequivocally identified and were shown to increase significantly when an eGFR declined to ≤17–23 mL/min/1.73m2. Serum concentrations of PTH1–84 were similar when measured by LC-HRMS following capture by amino-terminal or carboxyl-terminal immunocapture methods. In patients with an eGFR of <30 mL/min/1.73 m2, serum PTH concentrations measured using LC-HRMS were significantly lower than PTH measured using an iPTH immunoassay. PTH7–84 and oxidized forms of PTH1–84 were below the limit of detection (30 and 50 pg/mL, respectively).CONCLUSIONS:LC-HRMS identifies circulating PTH1–84, carboxyl-terminal PTH fragments, and mid-region PTH fragments, in patients with progressive renal failure. Serum PTH1–84 and its fragments markedly rise when an eGFR decreases to ≤17–23 mL/min/1.73 m2. PTH concentrations measured using LC-HRMS tend to be lower than those measured using an iPTH immunoassay, particularly in severe chronic renal failure. Our data do not support the existence of circulating PTH7–84 and oxidized PTH1–84.