Calcium/phosphate ratio: an additional tool for the clinical management of asymptomatic primary hyperparathyroidism?

Purpose: Serum calcium/phosphate ratio (Ca/P) has been recently proposed as an additional tool to identify primary hyperparathyroidism (PHPT), especially in patients with subclinical presentation, with a proposed cut-off of 3.3 when both values are expressed in mg/dL. No data are available on the relationship between Ca/P and the clinical presentation of PHPT. We thus evaluated this relationship in a large, single-center, unselected series.

Methods: 515 consecutive PHPT patients (mean age 65 ± 13.15 years, 77.1% females) were retrospectively evaluated at diagnosis.

Results: Mean Ca/P was 4.54 ± 1.5 (range 2.36-13.9), being higher than 3.3 in 88.5% of patients. Ca/P was significantly higher in (1) males, (2) symptomatic PHPT, (3) patients with 25-hydroxy vitamin D levels lower than 20 μg/L, (4) patients with osteitis fibrosa cystica, (5) patients with T score < - 2.5 at the radial site. In a multivariate regression analysis, Ca/P resulted significantly associated with PTH levels. After the exclusion of 57 patients with asymptomatic PHPT (aPHPT) patients and serum Ca higher than 1 mg/dL above the upper limit of normal range, no differences were found in Ca/P between aPHPT meeting or not surgical criteria.

Conclusions: In PHPT Ca/P ratio is associated with increased biochemical and clinical severity of disease and represents a direct indicator of clinical bone damage. However, it does not seem an additional tool to identify aPHPT patients reaching surgical indication.