BIOCHEMICAL DYNAMICS OF UNTREATED PRIMARY HYPERPARATHYROIDISM: AN OBSERVATIONAL STUDY.

The natural biochemical history of untreated primary hyperparathyroidism (PHPT) is poorly understood. The purpose of this study was to determine the extent of biochemical fluctuations in patients with PHPT. Retrospective cohort study from January 1, 1995, to December 31, 2014. Serum calcium and parathyroid hormone (PTH) levels in patients with classic (Ca >10.5 mg/dL, PTH >65 pg/mL) and nonclassic (Ca >10.5 mg/dL, PTH 40 to 65 pg/mL) PHPT were followed longitudinally at 1, 2, and 5 years. Biochemical profiles in follow-up were ranked in descending biochemical severity as classic PHPT, nonclassic PHPT, normal calcium with elevated PTH (Ca <10.5 mg/dL, PTH >65 pg/mL), possible PHPT (Ca >10.5 mg/dL, PTH 21 to 40 pg/mL), or absent PHPT (Ca >10.5 mg/dL, PTH <21 pg/mL or Ca <10.5 mg/dL, PTH <65 pg/mL). Of 10,598 patients, 1,570 were treated with parathyroidectomy (n = 1,433) or medications (n = 137), and 4,367 were censored due to study closure, disenrollment, or death. In the remaining 4,661 untreated patients with 5 years of follow-up, 235 (5.0%) progressed to a state of increased biochemical severity, whereas 972 (20.8%) remained the same, and 3,454 (74.1%) regressed to milder biochemical states. In 2,522 untreated patients with classic PHPT, patients most frequently transitioned to the normal calcium with elevated PTH group (n = 1,257, 49.8%). In 2,139 untreated patients with nonclassic PHPT, patients most frequently transitioned to the absent PHPT group (n = 1,354, 63.3%). PHPT is a biochemically dynamic disease with significant numbers of patients exhibiting both increases and decreases in biochemical severity. = interquartile range; = Kaiser Permanente Southern California; = primary hyperparathyroidism; = parathyroid hormone; = parathyroidectomy.