“Nephrolithiasis from an Unexpected Cause: Phosphaturia”

A 54-year-old woman with a history of Type 2 diabetes mellitus and breast cancer with bilateral mastectomy presented to the nephrology clinic for evaluation of nephrolithiasis. She was first diagnosed with nephrolithiasis 3 years prior to arrival requiring lithotripsy and treated with oral potassium citrate. On physical examination, she was a pleasant, middle aged woman with normal blood pressure, regular pulse and mild costovertebral tenderness bilaterally. Her laboratory studies were remarkable for serum creatinine of 1.29 mg/dl (normal value 0.5-1.2 mg/dl), serum calcium 10.7 mg/dl (normal value 8.8-10.7 mg/dl), serum albumin 4.9 g/dl (normal value 3.5-5.2 g/dl), serum phosphorus of 2.2 mg/dl (normal value 2.4-4.3 mg/dl), Parathyroid Hormone (PTH) 23 pg/ml (normal value 15-65 pg/ml), 25(OH) Vitamin D of 43 ng/ml (normal value 20-80 ng/ml), 1,25 (OH) Vitamin D of 80 pg/ml (normal value 18-78 pg/ml), Thyroid Stimulating Hormone 1.4 uIU/ml (normal value 0.5-5.7 uIU/ml), PTH-Related Peptide 0.3 pmol/L (normal value <2.0 pmol/L), and Fibroblast Growth Factor-23 153 RU/ml (normal value <180 RU/ml).