fractional excretion of phosphorus

Introduction

Defined as: excreted phosphorus/filtered phosphorus

Indications

• evaluation of hypophosphatemia

Clinical significance

• useful for renal phosphate wasting i.e. Fanconi syndrome, RTA-2 vs extrarenal cause of hypophosphatemia
• fractional excretion of phosphorus > 5% is consistent with renal phosphate wasting (RTA type 2)

Procedure

Measured as:

 (urine phosphorus/serum phosphorus) / (urine creatinine/serum creatinine)

More general terms

• urinary indices

Additional terms

• hypophosphatemia