Performance of the pro-FHH score in a delayed diagnosis of familial hypocalciuric hypercalcemia type-1

We present a case of a 50-year-old woman with familial hypocalciuric hypercalcemia type 1 (FHH-1) that was missed during an initial evaluation of hypercalcemia in the setting of normal serum parathyroid hormone (PTH), leading to unnecessary parathyroidectomy. She subsequently reported years later with an inappropriately elevated PTH in the setting of hypercalcemia. Sequencing of the calcium-sensing receptor (CASR) gene revealed a known inactivating variant associated with FHH-1. We assessed the clinical utility of the recently reported pro-FHH (Probability of having familial hypocalciuric hypercalcemia) score at the time of her surgery and subsequent re-evaluation years later. This case highlights the diagnostic challenges in differentiating familial hypocalciuric hypercalcemia from primary hyperparathyroidism (PHPT).