Reference methods in clinical chemistry.

For the measurements of analyses such as glucose, creatinine etc, in clinical chemistry, definitive methods and standard reference materials are available. On the other hand, for the measurements of the catalytic activity concentration of enzymes, various methods have been developed and those methods have generated a variety of results and reference ranges, difficulties in the interpretation of results, and difficulties in external quality assessment programs. Therefore, for the measurement of the catalytic activity of an enzyme, reference method is very important as the first start to obtain an accurate and precise result. We report the present situation of standardization for the measurement of the catalytic activity of enzymes and the comparison of reference methods including standards or consensus methods for the representative enzymes recommended by International Federation of Clinical Chemistry and the representative societies of clinical chemistry, and the survey results produced by Japan Medical Association.

Current status of liver function tests in Japan.

Inter-laboratory variations in data obtained from surveillance in Japan were studied. The items evaluated were related to liver function and were as follows: total bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyltransferase (gamma-GT), cholinesterase (CHE), lactate dehydrogenase (LD), alkaline phosphatase (ALP) and hepatitis markers. Inter-laboratory coefficients of variations for bilirubin, AST and ALT were acceptable, being less than 10%. but higher variations were found for thle other enzyme assays. Detection of hepatitis markers was acceptable. However. even for parameters with lower inter-laboratory variation, differences in obtained values among different reagents or methods still existed. Thus, standardization will be needed for laboratory data in Japan, and this will contribute to international standardization in laboratory medicine in the future.

External quality control results for hormones, tumor markers and CRP testing.

Most hormones, tumor markers, C-reactive protein, and rheumatoid factor (RF) are measured immunologically. Immunological methods based on the antigen-antibody reaction have certain specific problems, including their principle of determination, character of antibodies used, reaction conditions, and others. Free thyroxine (FT4) and thyroid stimulating hormone (TSH), as well as alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), prostate antigen, carcinoantigen 19-9 (CA 19-9), and CA 125 are very commonly measured in the routine medical laboratory. Authentic materials can be obtained for hormones and CRP, and efforts to improve quality control and standardization have been made for years. Results of surveillance for FT4, TSH, and AFP were not poor, but inter-laboratory differences for CEA, CA 19-9, and RF were not insignificant.

Quality of dry chemistry testing.

Since the development of the qualitative test paper for urine in 1950s, several kinds of dry-state-reagents and their automated analyzers have been developed. "Dry chemistry" has become to be called since the report on the development of quantitative test paper for serum bilirubin with reflectometer in the end of 1960s and dry chemistry has been world widely known since the presentation on the development of multilayer film reagent for serum biochemical analytes by Eastman Kodak Co at the 10th IFCC Meeting in the end of 1970s. We have reported test menu, results in external quality assessment, merits and demerits, and the future possibilities of dry chemistry.

Diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) for Chagas'disease serodiagnosis

Diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) was standardized and evaluated for the diagnosis of Chagas'disease in comparison with the conventional serological tests indirect immunofluorescence (IFI), passive hemagglutination (PHA) and complement fixation (CF). A total of 236 serum samples positive and negative for the serodiagnosis of Chagas'disease were studied. The group included 50 serum samples serologically positive for leishmaniasis and 36 positive for malaria. The best diagnostic performance of DIG-ELISA was observed when serum samples were diluted to 1:8 and a diameter of zero mm (no color) was taken as the cut-off. Under these conditions, the relative indices of sensitivity, specificity and agreement were 100%. High positive correlation coeficients were obtained between DIG-ELISA and IFI (r1=0.9010), PHA (r2=0.8943) and CF (r3=0.8269). We conclude that DIG-ELISA provides an alternative technique for screening chagasic infections, as well as for seroepidemiological surveys mainly because it is simple, easy to carry out and does not require expensive equipment