Normocalcemic primary hyperparathyroidism (nPHPT) is a phenotype of PHPT characterized by normal serum calcium and persistently increased parathyroid hormone (PTH) after exclusion of secondary causes of PTH elevation (SHPT). Functional diagnostic tests, including test with active vitamin D, could be useful in differential diagnosis between nPHPT and SHPT.
PURPOSE OF THE STUDY
The aim of this study was to investigate the capability of short test with active metabolites of vitamin D for differential diagnosis between nPHPT and SHPT for inpatient treatment.
MATERIAL AND METHODS
We included 90 hospitalized patients with normal albumin-adjusted calcium (Caadj) and elevated PTH levels (84 women, 6 men, median age 60 years). Caadj, PTH, creatinine, eGFR, daily calciuria were evaluated before and PTH, Caadj 3—5 days after taking 1 mcg of alfacalcidol or calcitriol.
RESULTS
According to baseline and dynamic biochemical evaluation patients were divided into 3 groups: group 1 — patients with elevated (n=28) or within the upper limit PTH (n=4) who reached hypercalcemia (Caadj>2.55 mmol/l); group 2 (n=14) — patients with normalization of PTH and normal Caadj; group 3 (n=44) patients with elevated PTH and normal Caadj. In group 1, baseline Caadj. was 2.52 mmol/l (2.50; 2.54), PTH 101.1 pg/ml (81.9; 138.0), after short test — 2.61mmol/l (2.58; 2.64), and 92.2 pg/ml (71.2; 119.5) respectively, regarded as PHPT. Among them 19 patients underwent surgery with histological confirmation of diagnosis. 2 patients are waiting for surgery, 11 patients with asymptomatic form are under dynamic observation. In group 2, baseline Caadj was 2.33 mmol/l (2.31; 2.44), PTH 81.1 pg/ml (72.9; 95.7) vs 2.40 mmol/l (2.33; 2.51) and 54.53 pg/ml (40.7; 63.6) respectively after short test regarded as SHPT. Groups with PHPT and SHPT significantly differed from each other in Caadj and daily calciuria (p<0.05) but not in PTH, eGFR. 44 patients from group 3 did not show significant changes thus differential diagnosis was continued on an outpatient basis.
CONCLUSION
The study showed the significant changes in calcium and PTH levels during the short test in 46/90 patients. Stable normocalcemia and normalization of PTH allows confirming SHPT while elevated or within the upper limit of PTH levels with hypercalcemia — PHPT.