Reference limits of the urinary gamma-glutamyltransferase in a healthy population and effects of short-term storage on the enzyme activity.

BACKGROUND: Gamma-glutamyltransferase (GGT) is present mainly in proximal renal tubule, and urinary GGT is an indicator of tubular damage since it may show renal changes before they are identified by using conventional measurements. Therefore, it is of interest to establish the reference limits of urinary GGT for a healthy population, as well as to investigate the stability of GGT in urine samples stored at 4 °C and -20 °C. METHODS: GGT was assessed in urine samples from 127 healthy patients by use of a reference method based on the 5-Amino-2-Nitrobenzoate formation. Stability of GGT was evaluated in 10 urine samples stored at temperatures of 4 °C and -20 °C for a period up to 4 weeks. RESULTS: Urinary GGT values for healthy volunteers were 14 U/g creatinine for the lower reference limit and 79 U/g creatinine for the upper reference limit. Urinary GGT values were approximately 56% lower in samples stored at -20 °C than fresh samples, while samples stored at 4 °C presented a decrease of 11% in GGT values compared to fresh samples. CONCLUSIONS: Reference limits for urinary GGT in healthy subjects were 14 to 79 U/g creatinine, and it is recommended to measure urinary GGT in fresh specimens.