An Improved Method for the Quantitation of Apolipoprotein B and Apolipoprotein A-1 in Dried Blood Spots

An extraction protocol has been developed to elute apolipoprotein B (apo B) and apolipoprotein A-1 (apo A-1) from dried blood spots with assay of the extracted apolipoproteins by automated immunoturbidimetry. Various extraction media were investigated to assess their elution efficiency and the optimum medium was found to be deionized water. Studies on the rate of elution suggested both apolipoproteins were eluted readily in less than an hour with a recovery of 71% for apo B and 65% for apo A-1. Extracted apo B but not apo A-1 was found to be stable for 24 h when kept at 4°C. The within-batch coefficients of variation (CV) for the combined extraction and assay of apo B were found to be 5·9% and 8·5% at 0·6 g/L and 1·2 g/L respectively. The CVs for apo A-1 were found to be 7·4% at 0·7 g/L and 8·9% at 1·5 g/L. Antiserum from three sources (Immuno, Incstar and Bayer) was investigated for immunoreactivity with apo B and apo A-1 and cross-reactivity with red blood cells was also assessed. Although the antisera from the three companies showed similar immunoreactivity towards apo B and apo A-1, antiserum from Bayer was found to cross-react with red cells.