International study on the comparability of Apo A-1 and Apo B methods

Apo A-1 and Apo B levels have become increasingly important as a mean of assessing risk and susceptibility to cardiovascular diseases. These proteins are measured routinely in numerous clinical and research laboratories due primarily to the ability to mechanise the immunological assay method and to the ready availability of commercially produced antisera and standards which are often sold in kit form. However, if these variables are to be used to assess the clinical risk of disease reliably, the test methods should have a low degree of imprecision and inaccuracy, to reduce false positive and negative results. The 'normal' and 'pathological' ranges for both proteins also need to be clearly defined. In order to be able to define clinical ranges and establish quality control limits on both a national and international level the inaccuracy and imprecision of the different methods used to assay the parameters need to be established. Since the technical expertise and the equipment and reagents used vary between laboratories, and because there is no internationally recognized calibration material, a survey conducted to establish imprecision and inaccuracy must include many laboratories to take these variations into account. At the WHO Collaborating Lipid Reference Centre, The Institute for Clinical and Experimental Medicine in Prague, Czechoslovakia, we have been involved in the external quality control programme for cholesterol, triglyceride, HDL-cholesterol and thiocyanate methods for more than 15 yr. Although the Centre was originally created as a European Reference Centre, laboratories participating in our quality control scheme now come from Asia, the USA and New Zealand as well as Europe due to their involvement in the large scale population studies like 'MONICA', 'ERICA' and 'CINDI'. In addition we also cooperate with some laboratories expected to join WHO projects and with others running either national or their own research programmes. Due to the increasing need to learn more about the methods used for Apo A-1 and Apo B assays in both research and preventive schemes for cardiovascular diseases, we decided, following the combined IUIS and NHLBI-CDC Apolipoprotein standardization surveys, to arrange for an international survey to determine the precision and relative accuracy of EIA, ELISA, INA, TURB and RID methods. Our survey originally intended to include only European laboratories but the number of participants increased (Table I) and we believe it supplies complementary information to the IUIS-NHLBI-CDC surveys because both research and routine clinical laboratories were included in our survey.