Diagnosis of Hypophosphatemic Rickets Serum levels of calcium, phosphate, alkaline phosphatase, 1, 25-dihydroxyvitamin D3, parathyroid hormone (PTH), FGF-23, and creatinine Urinary phosphate and creatinine levels (for calculation of the tubular reabsorption of phosphate) Bone x-rays Often genetic testing Serum phosphate levels are depressed, but urinary phosphate excretion is large.