Endocrine Abstracts

JOINT2437

Background: The differentiation of primary hyperparathyroidism (PHPT), normocalcemic primary hyperparathyroidism (NPHPT), and vitamin D deficiency-associated secondary hyperparathyroidism (VDSHPT) remains a diagnostic challenge. This study evaluates the diagnostic performance of biochemical markers in distinguishing these conditions.

Methods: This cross-sectional study included 437 participants categorized into PHPT (n = 161), NPHPT (n = 97), VDSHPT (n = 89), and control (n = 90) groups. Serum calcium (Ca), phosphate (P), chloride (Cl), parathyroid hormone (PTH), and vitamin D levels were analyzed, along with biochemical indices such as Cl/P, Ca/P, Ca × Cl/P ratios, and the PF Index (Ca × PTH/P). Patients with chronic kidney disease, malignancy, or medication use affecting calcium and PTH metabolism were excluded. Receiver operating characteristic (ROC) curve analysis was used to determine diagnostic accuracy.

Results: Calcium levels were highest in PHPT (2. 73 ± 0. 17 mmol/l, P < 0. 001), while phosphate levels were lowest (0. 70 ± 0. 19 mmol/l, P < 0. 001). PTH levels were significantly elevated in PHPT (164. 9 ± 73. 4 pg/mL), NPHPT (126. 0 ± 40. 4 pg/mL), and VDSHPT (134. 9 ± 49. 2 pg/mL) compared to controls (43. 2 ± 14. 0 pg/mL, P < 0. 001). The Ca/P ratio was highest in PHPT (4. 17 ± 1. 21), significantly differing from other groups (P < 0. 001). The Ca × Cl/P ratio was also significantly elevated in PHPT (448. 5 ± 133. 6) compared to controls and other hyperparathyroidism subtypes (P < 0. 001). No significant differences were observed between NPHPT and VDSHPT for Ca/P (P = 0. 63) and Ca × Cl/P (P = 0. 74) ratios. The Ca × Cl/P ratio exhibited the highest diagnostic accuracy for PHPT (AUC: 0. 876, 95% CI: 0. 834–0. 917), with a specificity of 89. 2% and PPV of 82. 2%. The Ca/P ratio had the highest sensitivity (77. 6%) and an NPV of 86. 6%. The PF Index (AUC: 0. 851, 95% CI: 0. 816–0. 886) and Cl/P ratio (AUC: 0. 766, 95% CI: 0. 711–0. 820) showed moderate accuracy. In contrast, all markers showed high sensitivity (100%) but extremely low specificity (1. 6–23. 2%) in NPHPT, with poor PPV (<27%) despite maintaining an NPV of 100%.

Conclusion: The Ca × Cl/P and Ca/P ratios demonstrate strong diagnostic value for PHPT, while biochemical markers have limited specificity in NPHPT. These findings highlight their role in screening but emphasize the need for additional diagnostic approaches.

Keywords: Primary hyperparathyroidism, Normocalcemic hyperparathyroidism, Vitamin D deficiency, Biochemical markers, ROC analysis, Parathyroid function index