The Ca∗Cl/P Ratio: A Novel and More Appropriate Screening Tool for Normocalcaemic or Overt Primary Hyperparathyroidism

Objective The main purpose of this study was to explore the diagnostic performance of the Ca*Cl/P ratio for primary hyperparathyroidism (PHPT), especially normocalcaemic primary hyperparathyroidism (NPHPT), to assist health-care providers in making reliable and rapid clinical identifications. Methods From January 1, 2013, to March 31, 2023, 230 PHPT patients, including 65 with NPHPT and 230 sex- and age-matched controls, were enrolled in this retrospective study. Differences between hypercalcaemic primary hyperparathyroidism (HPHPT) and NPHPT and between them and their respective controls were analysed. The diagnostic accuracy of the Ca*Cl/P ratio, Ca/P ratio, Cl/P ratio and albumin-corrected calcium was assessed by the area under the receiver operating characteristic curve (ROC-AUC). Results Compared with corresponding controls, NPHPT and HPHPT patients both had significantly higher Ca * Cl/P ratios (271.64±51.74 vs. 192.71±26; 419.91±139.11 vs. 199.14±36.75, p<0.001). In the overall cohort, the ROC-AUC of the Ca*Cl/P ratio (0.964, 95% CI = 0.943–0.979) for diagnosis of PHPT patients was superior to albumin-corrected calcium (0.959, 95% CI = 0.934–0.973), the Ca/P ratio (0.956, 95% CI = 0.934–0.973), and the Cl/P ratio (0.923, 95% CI = 0.895–0.946). A Ca * Cl/P ratio above 239.17 mmol/L, with sensitivity (0.952), specificity (0.922), PPV (0.924), NPV (0.951) and accuracy (0.937), can distinguish PHPT patients from healthy individuals. Furthermore, the Ca * Cl/P ratio yielded a sensitivity of 0.831, specificity of 0.938, PPV of 0.931, NPV of 0.847 and accuracy of 0.885 for NPHPT. Conclusion The Ca*Cl/P ratio provides excellent diagnostic power for diagnosis of PHPT, especially NPHPT.