Background: Nephrolithiasis is a classic, treatable manifestation of primary hyperparathyroidism (PHPT). We examined predictors of kidney stone formation in PHPT patients and determined how efficiently the diagnosis of PHPT is made in patients whose initial presentation is with stones.
Materials and methods: We performed a retrospective analysis of surgically treated PHPT patients, comparing 247 patients who were kidney stone formers and 1047 patients with no kidney stones. We also analyzed 51 stone-forming patients whose stone evaluation and treatment were completed within our health system before PHPT diagnosis.
Results: Stone-forming patients had higher 24-h urinary calcium (342 versus 304 mg/d, P = 0.005), higher alkaline phosphatase (92 versus 85 IU/L, P = 0.012), and were more likely to be normocalcemic (26.6% versus 16.9%, P = 0.001). Surprisingly, 47.3% of stone formers had normal urinary calcium levels (<300 mg/d). Of the 51 stone-forming patients treated at our institution, serum calcium was measured within 6 mo of stone diagnosis in 37 (72.5%) patients. Only 16 (31.4%) of these patients had elevated calcium levels, and only 10 (62.5%) of these 16 had a serum parathyroid hormone ordered within the following 3 mo. These patients had a significantly shorter time from their first stone to surgical treatment compared to other patients (median 8.5 versus 49.1 mo, P = 0.001).
Conclusions: Elevated serum and urinary calcium levels are not evaluated in the majority of PHPT patients presenting with kidney stones. In nephrolithiasis patients, provider consideration of PHPT with prompt serum calcium and parathyroid hormone evaluation significantly reduces time to treatment.
Keywords: Calcium; Kidney stones; Nephrolithiasis; PHPT; Primary hyperparathyroidism.
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