Endocrine Abstracts

Introduction: Primary hyperparathyroidism (PHPT) is a common endocrine disorder that is characterized by hypercalcemia and elevated or normal levels of parathyroid hormone (PTH). Most PHPT cases are incidentally discovered when routine laboratory analysis reveals hypercalcemia. PHPT should be considered in any person with elevated serum calcium (Ca) levels and no clear evidence of malignancy. Serum phosphorus (P) is low due to the phosphaturic effects of PTH and mostly in the lower half of the normal range. As serum Ca and P are inversely related in PHPT, we examined the diagnostic value of the serum Ca/P ratio in the diagnosis of PHPT.

Method: A total of 364 patients followed at our clinic with a diagnosis of PHPT were retrospectively analyzed. As a control group, we selected 98 patients who attended the clinic in the same time period, presenting serum PTH, Ca and P within the normal range. The main outcome measures were: serum Ca, P, albumin, PTH, 25-OH vitamin D and creatinine. Both patients with normocalcemic PHPT and hypercalcemic PHPT were included. The diagnostic accuracy of Ca/P was investigated using receiver operator characteristic (ROC) curve analysis. The resultant cut-off was verified using the independent set of data containing 100 patients and 50 control cases.

Results: There were 317 (87%) females and 47 (13%) males in patients group, and the mean age of the cohort was 53.9 ± 11.4 years (range: 20–82 ). Ca and PTH were significantly higher in PHPT than in controls (P < 0.0001). The Ca/P ratio was also significantly higher in PHPT than in controls (P < 0.0001). ROC curves analyses identified a cutoff value as 3.23 (mg/dl) for Ca/P ratio with a sensitivity and specificity of 94% and 93%, respectively (P < 0.0001). This cut-off value was confirmed by an independent group of cases (100 PHPT and 50 control cases) with 91% sensitivity and 80% specificity.

Conclusion: Ca/P is a precious predictor for the diagnosis of PHPT and it can be used instead of evaluating serum Ca and P levels solely. As Ca/P ratio is easily accessible and inexpensive, it will be useful for PHPT diagnosis and provide simplicity especially for thepractitioners with limited resources.