Preliminary investigations on the standardisation and quality control for the determination of γ‐glutamyltranspeptidase activity in seminal plasma

Summary The present study was designed to assess the effects of centrifugation velocity, standing time after dilution, freezing–thawing and chymotrypsin on the determination of γ ‐glutamyltranspeptidase ( γ ‐GT) activities in seminal plasma, and to establish an instruction for the standardisation and quality control for the determination of γ ‐GT within the same laboratory and among different laboratories. The γ ‐GT level and sperm concentration of each of 72 samples of seminal plasma obtained by centrifugation at 1000  g for 10 min or 3000  g for 15 min were assayed. In addition, γ ‐GT activities in diluted seminal plasma with different standing time and in samples with or without chymotrypsin were measured. The results showed that there was a significant difference of γ ‐GT levels in seminal plasma obtained by centrifugation at different velocities ( P  < 0.001), and that γ ‐GT activities in seminal plasma measured after standing for 30 min after dilution were notably lower than those measured immediately after dilution ( P  < 0.001). However, the data indicated that both chymotrypsin and freezing–thawing had no apparent effect on the determination of seminal γ ‐GT. In conclusion, standing time after dilution and centrifugation velocity should be standardised, and frozen seminal plasma could serve as quality control products for the determination of γ ‐GT activity among different laboratories.