Predictors of Renal Function and Calcifications in Primary Hyperparathyroidism: A Nested Case-Control Study

Context: Some patients with primary hyperparathyroidism (PHPT) develop renal calcifications. Investigation of urinary and nonurinary risk factors are essential. Objective: We aimed to study the prevalence and potential biochemical predictors of renal calcifications. Design: Nested case-control study. Setting: University hospital. Participants: We identified 792 patients with PHPT from 2005 to 2015. We used biochemical data to validate the diagnosis of PHPT. Main Outcome Measures: The prevalence of renal calcifications defined as nephrolithiasis or nephrocalcinosis assessed by a routine CT scan at the time of diagnosis. Results: A total of 792 patients with PHPT were identified among whom 617 patients (78%) had a CT scan preformed. We found a prevalence of renal calcifications of 23%, equally frequent between sexes. A total of 76 patients (12%) had nephrolithiasis and 75 patients (12%) had nephrocalcinosis where 7 patients (1 %) had both nephrolithiasis and nephrocalcinosis. Compared with patients without renal calcifications, patients with renal calcifications had significantly higher levels of all v ionized calcium, parathyroid hormone, and 24-hour calcium excretion (P-all < 0.01). Patients with nephrocalcinosis had higher plasma levels of phosphate and a higher calcium-phosphate product compared with patients with nephrolithiasis (P-all < 0.05). Impaired renal function (estimated glomerular filtration rate <60 mUmin) was observed in 12% of patients. However, no differences in renal function were observed between those with and without renal calcifications. Conclusion: Renal calcifications are frequent in patients with PHPT and are associated with the severity of the disease. Impaired renal function is also common in PHPT, but renal function was not associated with renal calcifications.