Net acid excretion

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In renal physiology, net acid excretion (NAE) is the net amount of acid excreted in the urine per unit time. Its value depends on urine flow rate, urine acid concentration, and the concentration of bicarbonate in the urine (the loss of bicarbonate, a buffering agent, is physiologically equivalent to a gain in acid). NAE is commonly expressed in units of milliliters per minute (ml/min) and is given by the following equation:


Variable Meaning
NAE net acid excretion
V volume of urine produced per unit time
UNH4 urine concentration of ammonium
UTA urine concentration of titratable acid (e.g., phosphoric acid, sulfuric acid)
UHCO3 urine concentration of bicarbonate


Increased net acid excretion is a compensation for respiratory acidosis, while decreased net acid excretion is a compensation for respiratory alkalosis.[1]