Fractional Excretion of Sodium (FENa) Test Price in Mission Road

Test Description

The Fractional Excretion of Sodium (FENa) is a calculated parameter that measures the fraction of sodium filtered by the glomerulus that is ultimately excreted in the urine, reflecting the kidney's ability to reabsorb sodium. FENa (%) = [(Urine Na × Serum Creatinine) / (Serum Na × Urine Creatinine)] × 100. FENa requires simultaneous spot urine Na and Cr, and serum Na and Cr measurements. FENa is the most widely used test to differentiate prerenal azotemia from acute tubular necrosis (ATN) in the setting of oliguria and rising serum creatinine. FENa <1%: indicates prerenal azotemia (intact tubular function aggressively reabsorbing sodium in response to low GFR — volume depletion, heart failure, hepatorenal syndrome, early bilateral ureteral obstruction). FENa >2%: indicates intrinsic renal injury (ATN) where tubular cells are damaged and unable to reabsorb sodium. Limitations: FENa may be falsely low (<1%) in ATN in the presence of contrast nephropathy, myoglobinuria, hemoglobinuria, and acute glomerulonephritis. In patients on diuretics (which increase FENa), the Fractional Excretion of Urea (FEUrea) is a better discriminator: FEUrea <35% = prerenal; >50% = ATN.