Laboratory Data

1. Total calcium and serum albumin or ionized calcium. Each gram per deciliter of albumin changes the serum calcium level by 0.8 mg/dL. Hypercalcemia is characterized as follows:

2. Phosphorus. Low serum phosphorus points to parathyroid hormone (PTH)-mediated causes, and high serum phosphorus points to vitamin D-mediated causes. Low phosphorus in a premature infant is indicative of phosphate depletion.

3. Alkaline phosphatase. Level is very low in hypophosphatasia but elevated in hyperparathyroidism.

4. BUN and creatinine. Evaluate for renal failure and dehydration as a guide for therapy.

5. Serum PTH. Elevated in hyperparathyroidism; suppressed by nonparathyroid diseases.

6. Vitamin D. Vitamin D intoxication is indicated by high 25-hydroxyvitamin D level.The level of 1,25-dihydroxyvitamin D may be elevated in granulomatous disorders or rare disorders, especially in infants, but this value is not as useful as 25-hydroxyvitamin D level.

7. Urine calcium, phosphorus, and creatinine. Perform on spot sample. Low calcium points to FHH; low tubular reabsorption of phosphate is consistent with a parathyroid disorder.

8. Other workup. Perform studies on parents if neonatal hypercalcemia is present. Obtain maternal and paternal serum and urinary calcium levels to diagnose FHH or familial hyper-parathyroidism.

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