Urinary protein and enzyme excretion as markers of tubular damage

In this review we intend to evaluate the clinical usefulness of measurement of urinary excretion of microproteins and tubular enzymes.

Studies of patients with acute tubular necrosis showed that the excretion of some well known enzymes and of new markers such as kidney injury molecule-1 has higher value than classic renal function tests for the early detection of the disease as well as for the prediction of the development of overt acute renal failure. Tubular dysfunction may be detected by measurement of the excretion of tubular enzymes and microproteins not only in workers chronically exposed to heavy metals but also in population exposed to low environmental level below the limits set by the WHO. In chronic glomerulonephritis the excretion of alpha1-microglobulin is significantly associated with the extent of tubulo-interstitial damage and predicts outcome better than proteinuria/day; in the same diseases NAG excretion is significantly dependent on immunoglobulin G and alpha1-microglobulin excretion and predicts remission, progression and response to therapy.

The measurement of urinary excretion of tubular enzymes and microproteins may be clinically useful in several different kidney diseases (such as acute tubular necrosis, glomerulonephritis) both for diagnosis and prediction of fractional outcome.