Combi scheme: new combined internal/external quality-assessment scheme in The Netherlands.

The Dutch Foundation for Quality Assessment in Clinical Chemistry (SKZL) is the professional organization that conducts external quality-assessment schemes in The Netherlands. However, such schemes in fact assess the performance of the internal quality-control systems of the participating laboratories. In this paper we describe a new concept, relating the data for internal control materials with those for external samples and thereby leading to a combined external/internal scheme (Combi). The statistical principles underlying the Combi scheme are discussed and examples of the graphical presentation of the results are shown. Because the laboratory data are transmitted over the public telephone system to the computers of the SKZL, we also describe the principles of the data communication. At two-month intervals a statistical presentation is sent to all participants. The central database is updated daily with the received results, making possible an on-line consultation regarding the statistics of the accumulated findings of the control materials in use.

Behaviour of L-gamma-glutamyl-4-nitroanilide and L-gamma-glutamyl-3-carboxy-4-nitroanilide with respect to gamma-glutamyltransferases of different origin.

In this paper we compare the measurement of catalytic activity concentrations of gamma-glutamyltransferase with the non-carboxylated and the carboxylated substrate in preparations of different origin. Fresh human sera, commercial test sera and preparations of gamma-glutamyltransferase purified from human liver, porcine kidney and bovine kidney were used as sample materials. When assayed with both substrates preparations of gamma-glutamyltransferase from bovine kidney behaved in a different manner as did the enzyme in preparations from human liver or porcine kidney and the enzyme in fresh human sera. On account of the results obtained with both substrates we classified the commercial test sera for their enrichment using multi-inductive component analysis. The differences observed for the various methods of determination seem to have significance in quality control.

Simultaneous spectrophotometric calibration of wavelength and absorbance in an interlaboratory survey using holmium oxide (Ho2O3) in perchloric acid as reference, compared with p-nitrophenol and cobaltous sulphate solutions (1978-1984).

The wavelength accuracy of ten different types of spectrophotometer was tested with holmium perchlorate solutions. It was found to be good, with mean deviations from the literature values of maximally 0.3 nm. Standard deviations over the entire spectral range were within 0.75 nm. The absorbance accuracy for different types of instruments was generally within 5%, except in the 287 nm range where higher deviations were found. The sharpness of the holmium peaks, in combination with band width and sensitivity of the instruments, troubled the majority of the participants. 150 spectrophotometers were involved in the surveys. Linearity of the spectrophotometers was tested with p-nitrophenol and cobaltous sulphate and found to be satisfactory.