Title: Diagnostic Performance of the Parathyroid Function Index, Wisconsin Index, and Calcium/Phosphate Ratio in Differentiating Primary hyperparathyroidism from Vitamin D-Deficient Secondary Hyperparathyroidism: A Study of 106 Cases
Authors: Leila Rouimi , Khawla Salhi , Mohammed Amine Essafi --, Zineb El Azime -- , Hayat Aynaou -- , Houda Salhi --
Volume: 10
Issue: 7
Pages: 33-37
Publication Date: 2026/07/28
Abstract:
Background: Serum 25-hydroxyvitamin D (25OHD) levels significantly influence parathyroid hormone (PTH) levels in primary hyperparathyroidism (PHPT). Vitamin D repletion to exclude secondary hyperparathyroidism (SHPT) is essential, particularly with the emergence of normocalcemic primary hyperparathyroidism (normocalcemic PHPT). This may delay the diagnosis of PHPT; diagnostic tools such as Pf index : Parathyroid Function Index, the WIN index, and the calcium-to-phosphate (Ca/P) ratio may facilitate early diagnosis.Aims: evaluate the diagnostic accuracy of these three tools in differentiating between primary hyperparathyroidism and vitamin D deficiency-induced secondary hyperparathyroidism, and to establish a diagnostic cutoff threshold to avoid overdiagnosis of primary hyperparathyroidism and thereby prevent unnecessary parathyroidectomies. Patients and Methods: Our retrospective comparative analytical study included 106 patients followed for primary hyperparathyroidism or vitamin D deficiency-induced secondary hyperparathyroidism. Patients were divided into three groups as follows: Group 1: PHPT, Group 2: normocalcemic PHPT (NC-PHPT), and Group 3: vitamin D deficiency-associated SHPT. The WIN index (Ca × PTH), the calcium-to-phosphate ratio (Ca/P), and the Pf index (Ca × PTH / phosphate) were calculated and analyzed across the three groups. Statistical analysis was performed using SPSS version 26 software. Quantitative variables among the three groups were compared using ANOVA test. The diagnostic performance of the different indices was evaluated using Receiver Operating Characteristic (ROC) curve analysis, with assessment of the balance between sensitivity and specificity. A p-value of 0.05 was used to determine statistical significance. Main results: Group 1 had the highest values of corrected serum calcium, PTH, and Pf index (p < 0.05). The WIN index was significantly higher in Group 1 compared to Group 2 (p = 0.003) and Group 3 (p < 0.001). The corrected Ca/P ratio was significantly higher in Group 1 compared to Group 3 (p < 0.001). Finally, the Pf index was significantly higher in Group 1 compared to Groups 2 and 3 (p = 0.002). The area under the ROC curve (AUC) for the Pf index in ROC analysis for the diagnosis of PHPT was the highest at 0.845. Accordingly, it provided a sensitivity of 89% and a specificity of 60% above the cutoff value of 59. A Ca/P ratio > 3.2 suggested PHPT with a sensitivity of 80% and a specificity of 70%. A WIN index > 51 suggested PHPT with a sensitivity of 88% and a specificity of 70%. Conclusion: The Pf index provided excellent diagnostic accuracy in differentiating PHPT from vitamin D deficiency-associated SHPT. This simple tool may be useful in guiding timely decision-making processes regarding the initiation of vitamin D supplementation versus parathyroidectomy for PHPT.