Is biochemical screening enough to guide calcium-sensing receptor gene mutational analysis when diagnosing familial...

The American Association of Endocrine Surgeons suggests screening for familial hypocalciuric hypercalcemia for 24-hour urine calcium <100 mg and for calcium to creatinine clearance ratio <1%. We explored the biochemical and clinical profiles of genetically tested patients to determine the usefulness of these recommendations.

This was a retrospective review of patients who underwent analysis of the calcium-sensing receptor gene.

In total, 401 patients were identified between 2005 and 2024; 332 (83%) were negative for a mutation, 44 (11%) were positive, and 25 (6%) had variants of unknown significance. Median serum calcium was lower in patients who were negative (negative 10.1 mg/dL, variants of unknown significance 10.6 mg/dL, positive 10.9 mg/dL). Median urine calcium was lower in patients who were positive (negative 110 mg, variants of unknown significance 149 mg, positive 82 mg). Median parathyroid hormone levels were comparable between groups (negative 65 pg/mL, variants of unknown significance 58 pg/mL, positive 60 pg/mL). Eight of 21 (38%) patients who tested positive had urine calcium >100 mg and 5 of 21 (24%) had urine calcium >200 mg. Eight of 35 (23%) patients who were positive had a calcium to creatinine clearance ratio >1%. Urine calcium and calcium to creatinine clearance ratio receiver operating characteristic curves showed poor performance in identifying patients with familial hypocalciuric hypercalcemia (area under the curve [95% confidence interval]): 0.55 [0.45-0.65] and 0.63 [0.57-0.7], respectively. For positive patients with imaging, sestamibi was inconclusive or nonlocalizing for 13 of 23 and showed multiglandular disease for localizing scans in 7 of 10. Ultrasound was nonlocalizing or equivocal for 11 of 13. In total, 212 of 401 patients (53%) underwent surgery; 100 of 212 were tested preoperatively (0/100 positive, 5/100 variants of unknown significance) and 112 of 212 patients were tested postoperatively (15/112 positive, 10/112 variants of unknown significance).

Familial hypocalciuric hypercalcemia demonstrates non-negligible biochemical overlap with primary hyperparathyroidism, with many patients having a urine calcium value greater than the American Association of Endocrine Surgeons suggested threshold for considering genetic evaluation. More frequent genetic testing beyond urine measurements may help identify more patients with familial hypocalciuric hypercalcemia.