Hypercalcemia: is defined as serum calcium >10.3 mg/dL

PTH should be performed

If the PTH is high:

• Primary hyper-parathyroidism or Familial benign hypercalcemia.
• To differentiate, we determine urinary calcium which will be high in Primary hyper-parathyroidism and low in Familial benign hypercalcemia.

If the PTH is low:

• Order Parathyroid Hormone-Related Peptide (PTHrP).
• High PTHrP is suggestive of cancer.
• Low/normal PTHrP order Vitamin D: Low results are suggestive of cancer while high values are suggestive of lymphoma or granulomatous disease (ex. Sarcoidosis).

Hypocalcemia: Serum calcium < 8.2 mg/dL

• Check serum albumin and calculate the corrected calcium

                  If low corrected calcium: determine intact Parathyroid hormone (PTH), creatinine (Cr), phosphorus (P) and Magnesium (Mg).

• Low PTH, normal Cr, normal/high P and low Mg: Magnesium deficiency.
• Low PTH, normal Cr, normal/high P and normal Mg: Hypo-parathyroidism.
• Normal PTH, normal Cr, normal/low P, normal Mg and low albumin: Hypo-albuminemia
• High PTH, normal Cr, Normal/low P and normal Mg: check vitamin D deficiency.
• High PTH, high Cr, normal/high P and normal Mg: Renal Disease or pseudo-hypo-parathyroidism