Urinary excretion of NAG and FDP in acute renal graft rejection

Determination of the urinary excretion of N-acetyl-D-glucosaminidase (NAG) and fibrin degradation products (FDP) made it possible to make a diagnosis of 25 out of 26 acute rejection episodes at least 24 hr before deterioration in renal function occurred. Of the two tests, the estimation of daily urinary NAG is the most practical for routine clinical use. This test alone permitted early diagnosis in 21 out of 26 episodes. In 9 out of 11 episodes in which both estimations showed an increase, the rise in FDP occurred before the rise in NAG. This is consistent with the view that in some forms of rejection, at least, intravascular fibrin deposition occurs first and causes ischaemic damage to renal tubular cells and consequent deterioration in function.