Review the following serum and urine laboratory profiles for four different adult patients. Reference ranges: Calcium 8.4-10.2 mg/dL, Intact PTH 10-65 pg/mL, Phosphorus 2.7-4.5 mg/dL, Creatinine 0.6-1.2 mg/dL; normal 24-hour urine calcium is typically 100-300 mg/day. Match each laboratory profile with the most likely clinical diagnosis.
- Profile A: Calcium 11.4 mg/dL, PTH 90 pg/mL, Phosphorus 2.0 mg/dL, Urine Calcium 350 mg/24hPrimary hyperparathyroidism
- Profile B: Calcium 10.9 mg/dL, PTH 75 pg/mL, Phosphorus 2.4 mg/dL, Urine Calcium 45 mg/24hFamilial hypocalciuric hypercalcemia
- Profile C: Calcium 7.6 mg/dL, PTH 145 pg/mL, Phosphorus 5.8 mg/dL, Creatinine 3.4 mg/dLSecondary hyperparathyroidism due to chronic kidney disease
- Profile D: Calcium 7.8 mg/dL, PTH 11 pg/mL, Phosphorus 5.2 mg/dL, Creatinine 0.9 mg/dLPrimary hypoparathyroidism
Answer
Profile A matches Primary hyperparathyroidism, Profile B matches Familial hypocalciuric hypercalcemia, Profile C matches Secondary hyperparathyroidism due to chronic kidney disease, and Profile D matches Primary hypoparathyroidism.
The correct matches reflect the physiologic relationships between PTH, calcium, and phosphorus. Primary hyperparathyroidism involves autonomous PTH driving high serum calcium, low phosphorus, and high urine calcium. FHH shares the serum profile but features low urine calcium due to altered receptor sensing in the kidneys. CKD causes hypocalcemia and high phosphorus, which drives up PTH secondarily. Primary hypoparathyroidism involves a direct lack of PTH, causing hypocalcemia and hyperphosphatemia.
Step-by-Step Solution
Key Concept
Differential diagnosis of calcium and parathyroid hormone disorders utilizing serum chemistries and urinary calcium excretion.