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The IFCC Committee on Plasma Proteins has been investigating regional differences for commonly assayed plasma proteins to determine whether universal reference intervals can be applied. As a part of this study, we launched an Asian project analyzing the concentrations of 13 serum proteins whose values are standardized to CRM470, and five newer analytes: retinol-binding protein (RBP), cystatin C (CysC), light- chain-Κ (L-Κ), and light-chain-λ (L-λ). In Tokyo, Seoul, Kuala Lumpur, Hong Kong, Taipei and Shanghai, serum samples were collected from 146 to 415 apparently healthy individuals with nearly equal gender ratios. All assays were performed in Tokyo on a Behring Nephelometer II (BN II). Seven chemical analytes (aspartate aminotransferase (AST), alanine amino- transferase (ALT), -γ-glutamyltransferase (-γGT), creatinine, total cholesterol (TC), triglycerides (TG) and high-density lipoprotein cholesterol (HDL-C)) were also measured. These results were used for excluding individuals with possible latent clinical disorders. Positive acute phase reactants were consistently lower, and negative ones were higher, in Tokyo than those in other cities. The most conspicuous difference was observed in C-reactive protein (CRP). There were no regional differences in transferrin, albumin, or CysC. Creatinine was much lower in Tokyo despite comparable CysC levels. ALT and -γGT were higher in Shanghai, Taipei and Seoul; -γGT and TG were higher in Shanghai; and HDL-C was higher in Tokyo. Gender-related differences in reference intervals were observed for immunoglobulin (Ig)M, haptoglobin, RBP, transferrin, α2-macroglobulin (A2M), transthyretin, α1-acid glycoprotein, CysC, and C4 in all cities. Slight age-related differences were observed, irrespective of the region, in IgA and ceruloplasmin (increase) and A2M (decrease). Environmental factors and lifestyle seem to have a great influence on many commonly measured analytes. [ABSTRACT FROM AUTHOR]