Lab Value


A 33-year-old woman has had elevated serum calcium levels since birth. Further evaluation demonstrates a normal PTH and hypocalciuria. She denies any symptoms.

What is the most appropriate treatment?

The patient described in the question has familial hypocalciuric hypercalcemia (FHH) disease. This is an autosomal dominant disease that expresses itself as an error in the calcium-sensing receptor (CASR). This will cause the baseline serum calcium level to be higher than normal. These patients are generally asymptomatic. Key laboratory findings include hypercalcemia, hypocalciuria, and normal to slightly elevated PTH levels.
The diagnosis of FHH is suspected when 24-hour urinary calcium is low despite the elevated blood levels of calcium. A calcium and creatinine ratio is then determined using the following equation:

(Urinary calcium/PLASMA calcium) × (Plasma creatinine/Urinary creatinine) = Ca/Cr clearance ratio

If this ratio is 0.02 or less, then genetic counseling is warranted and genetic testing for mutations in the CASR gene may be recommended. Genetic testing is especially helpful in patients with a ratio between 0.01 and 0.02 where differentiating FHH from PHPT is not possible. It is important to identify patients with FHH, because they do not benefit from surgery.