The recommended method for measuring the activity of serum γ-GT was established by Japan Society of Clinical Chemistry (JSCC). This method was based on the IFCC method, and the final concentration of GluCANA as a donor substrate and that of glycylglycine as an acceptor substrate were set at 6.0 mmol/ 1 and 150 mmol/ 1 respectively. The initial velocity under these conditions was about 77% of Vmax. However, it is inappropriate to increase further the concentrations of the substrates, because of unacceptable increasing absorbance of reagent blank.
This method has the following two characteristics. One is that the amount of the sample was set small so as to avoid the turbidity to becaused by the reaction between glycylglycine and the serum, and the other is that the procedure is two-step system in which the reaction is made to start by GluCANA as the donor substrate.
It was confirmed that there was no difference in the measurement value obtained by this recommended method and the IFCC method. Therefore, this method will be used for traceability to the IFCC method. The consensus method, which is derived from this recommended method by setting the reaction temperature at 37°, will be used for traceability of the measured value by the field method. Furthermore, the consensus method is also used for valuating the enzyme reference materials and for checking of commutability.
