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.