The impact of hypophosphatemia on biochemical profile and renal outcomes in primary hyperparathyroidism: a nationwide retrospective study.

Background/aim: Although low phosphorus (P) concentrations are a recognized feature of primary hyperparathyroidism (PHPT), they are not among the diagnostic or surgical criteria. The present study evaluates the association between serum phosphorus levels and clinical outcomes in PHPT patients. Materials and methods: A search of the Turkish Ministry of Health's National Electronic Database was conducted using ICD-10 diagnostic codes and laboratory data to identify PHPT cases within the Turkish population from 2017 to 2022. Results: The records of a total of 113,330 PHPT patients (77.5% female; mean age 58.9 ± 15.6 years) were analyzed, revealing a mean serum phosphorus level of 3.24 ± 0.79 mg/dL. Patients with nephrolithiasis, vitamin D <20 μg/L, and calcium ≥11.4 mg/dL had significantly lower phosphorus levels (p<0.0001). Hypophosphatemia (HypoP) (P < 2.5 mg/dL) was present in 14.3% of patients and was associated with higher parathyroid hormone, calcium, and alkaline phosphatase levels, and lower vitamin D levels (all p < 0.0001). HypoP independently increased the risk of kidney stone formation (OR = 1.53; 95% CI 1.46-1.61). Conclusion: HypoPis associated with more severe biochemical abnormalities and a greater prevalence of nephrolithiasis in PHPT. In regions where vitamin D deficiency is common, low phosphorus levels may indicate more severe diseases, and so routine phosphorus monitoring should be considered as part of PHPT management.