Clinical and laboratory characteristics of calcium stone-formers with and without primary hyperparathyroidism

To compare the clinical presentation, laboratory features and outcome of treatment in stone formers (SF) with primary hyperparathyroidism (HPT) to those without systemic disease.

We compared 105 (54 female) stone-formers (SF) with primary hyperparathyroidism (HPT) to 2416 (835 female) common SF with no systemic disease, and 260 normal subjects (NS, 106 female) using pre-treatment and treatment data from our kidney-stone programme. All were assessed before treatment, with three 24-h urine samples, for stone risk factors, each with a corresponding fasting blood sample. Records were reviewed for stone rates and urological stone-related procedures.

The hypercalcaemia of HPT was modest, but hypercalciuria was far more marked than in SF because the fractional calcium excretion of HPT exceeded that of SF. Surgical cure of HPT did not completely eradicate either hypercalciuria or hypophosphataemia, suggesting that these patients have some additional mineral disorder. Serum calcium and phosphate, and fractional excretion of calcium, combined into a discriminant function provided the best separation between HPT and SF. However, we present 49 patients for whom the diagnosis (HPT vs SF) has never been resolved, despite years of observation and successful reduction of stone recurrence. Stones in HPT have slightly more phosphate than SF but the difference is not large enough to be of clinical interest. The stone frequency in HPT is about that for SF, and treatment reduces stones in HPT and SF by about the same amount, 10 times.

No study to date has compared HPT with SF and NS, as done here. SF with even slight hypercalcaemia and brisk hypercalciuria probably have this curable disease, and after cure clinicians must be wary of residual hypercalciuria that requires medical treatment. Some patients will never be fully diagnosed and remain, like ours, an enigma, albeit responsive to usual medical treatments. Although stones are modestly enriched with phosphate, most are mainly calcium oxalate, so the stone analysis is not clinically a guide to diagnosis.