CST3 and Hypercalcemia: 24-h urine collection for calcium excretion. Parathyroid Hormone (PTH) and PTH-related peptide (PTHrP) Serum creatinine (and/or cystatin C)  Serum calcium and albumin levels should be measured and the ionized calcium calculated.  Renal Ultrasound to exclude nephrolithiasis Age appropriate malignancy work up (To rule out hypercalcemia secondary to malignancy)