Adoption of a manual kinetic gamma-glutamyl transferase method in the clinical laboratory.

Following our recommended protocol for establishing analytical methods in a clinical laboratory, a rapid, simplified manual kinetic method for determining Gamma-Glutamyl Transferase activity in serum was adopted to meet the needs of our laboratory. The steps taken, from the selection of the assay conditions through the introduction of the new test ot staff physicians, are described. The assay, which requires only 50 microliter of serum or plasma, uses L-gamma-glutamyl-p-nitroanilide as the substrate, and is controlled at 30C and a pH of 8.20. The reaction is monitored by the increase in absorbance at 405 nm. Up to 30 samples per hour may be analyzed using a manual spectrophotometer. The substrate is simple to prepare and is stable for one working day at room temperature and for at least one month for frozen at -20C.