net acid excretion net acid excretion 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: n a e = v ( u n h 4 + u t a − u h c o 3 ) +u_-u_)} where variablemeaning naenet acid excretion vvolume of urine produced per unit time unh4urine concentration of ammonium utaurine concentration of titratable acid (e.g., phosphoric acid, sulfuric acid) uhco3urine concentration of bicarbonate pathology increased net acid excretion is a compensation for respiratory acidosis, while decreased net acid excretion is a compensation for respiratory alkalosis.