A stabilising factor for gamma-glutamyl transpeptidase in urine.

Urinary gamma-glutamyl transpeptidase (gamma-GT) has been found to be stable when stored at room temperature and 4 degrees C. Activity is lost rapidly when urine is frozen but prior dialysis will prevent this loss. Urea is the major factor responsible for the loss of activity; albumin is protective at concentrations of 6 g/l or more. A factor of 10 000-30 000 molecular weight which will prevent the loss of urinary gamma-GT activity on freezing has been found in serum and urine; it has high potency in serum and in urine from patients with chronic renal failure, but only low potency in normal urine. Its nature is unknown but it is heat stable.