A clinical investigator is reviewing the laboratory records of four distinct patients evaluated for abnormalities in bone and mineral metabolism. Match each patient's serum and urine laboratory profile to the most likely underlying pathophysiologic diagnosis.
- Profile 1: Calcium 11.2 mg/dL, Phosphorus 2.1 mg/dL, Intact PTH 85 pg/mL (Normal: 10-65), 24-hour urine calcium 350 mg/day (Normal: 100-300)Primary hyperparathyroidism
- Profile 2: Calcium 11.0 mg/dL, Phosphorus 3.0 mg/dL, Intact PTH 55 pg/mL (Normal: 10-65), 24-hour urine calcium 40 mg/day (Normal: 100-300)Familial hypocalciuric hypercalcemia (FHH)
- Profile 3: Calcium 8.1 mg/dL, Phosphorus 2.2 mg/dL, Intact PTH 130 pg/mL (Normal: 10-65), 25-hydroxyvitamin D 12 ng/mL (Normal: 20-50)Secondary hyperparathyroidism (Vitamin D deficiency)
- Profile 4: Calcium 7.4 mg/dL, Phosphorus 5.4 mg/dL, Intact PTH 9 pg/mL (Normal: 10-65), 25-hydroxyvitamin D 30 ng/mL (Normal: 20-50)Primary hypoparathyroidism
Answer
Profile 1 matches Primary hyperparathyroidism; Profile 2 matches Familial hypocalciuric hypercalcemia; Profile 3 matches Secondary hyperparathyroidism; Profile 4 matches Primary hypoparathyroidism.
Each laboratory profile uniquely isolates a distinct pathology within the calcium-PTH feedback loop. Profile 1 shows autonomous PTH secretion (Primary hyperparathyroidism). Profile 2 shows an altered calcium-sensing set point (FHH). Profile 3 shows an appropriate physiological response to external deficiency (Secondary hyperparathyroidism). Profile 4 shows primary glandular failure (Primary hypoparathyroidism).
Step-by-Step Solution
Key Concept
Interpretation of the calcium-PTH axis and 24-hour urinary calcium excretion to differentiate primary, secondary, and receptor-mediated parathyroid disorders.