Clinical Chemistry - Case Study

Persistent Hypercalcemia: Choose Your Testing Strategy Carefully

Summary

https://doi.org/10.1093/clinchem/hvad008

A 50-year-old male was evaluated for mild, intermittent hypercalcemia, first identified 10 years earlier. He denied use of thiazide diuretics or lithium and did not have a history of kidney stones, low bone density, or fragility fractures. He denied symptoms of hypercalcemia and his past medical history was significant only for hypertension. Consistent with previous evaluations, laboratory values included a serum calcium of 10.5 mg/dL (8.6–10.2) (2.63 mmol/L [2.15–2.55]), ionized calcium of 1.43 mmol/L (1.18–1.33), albumin of 4.5 g/dL (3.8–5.0) (45 g/L [38–50]), and intact parathyroid hormone (PTH) of 36.9 pg/mL (15.0–72.0) (3.91 pmol/L [1.59–7.64]). Plasma phosphorus was not measured during this encounter but chart review revealed a value of 2.6 mg/dL (2.4–4.7) (0.84 mmol/L [0.78–1.52]) 6 months earlier. A 24 h urine specimen revealed a calcium of 111.6 mg/24 h (110–321) (2.78 mmol/24 h [2.74–8.01]) and creatinine of 1458 mg/24 h (1040–2350) (12.9 mmol/24 h [9.2–20.8]). The calcium to creatinine clearance ratio was 0.007. The complete set of laboratory values is documented in Table 1. Of note, the patient’s sister and daughter both had mild hypercalcemia. The patient had previously undergone calcium-sensing receptor gene (CASR) sequencing but no pathogenic variants were detected.