BioVision’s Human Apolipoprotein E4 (ApoE4) Enzyme-Linked Immunosorbent Assay (ELISA) Kit is an in vitro assay for quantitative measurement of human ApoE4. ApoE transports lipoproteins, fat-soluble vitamins, and cholesterol via the lymph system to the blood. ApoE exists as three major isoforms, including ApoE2, ApoE3, and ApoE4. Recently, ApoE4 has been implicated in Alzheimer's disease (AD). ApoE4 is the first risk gene identified in Alzheimer's research, and remains the gene with strongest impact. Everyone inherits a copy of ApoE gene from each parent. Those who inherit one copy of ApoE4 have an increased risk of developing AD (about a quarter of the human population). Those who inherit two copies of ApoE4 have an even higher risk (about 2% of humans with up to 10 times higher risk). In addition to raising risk, ApoE4 may tend to make AD symptoms appear at a younger age. The assay employs an antibody specific for human ApoE4 coated on a 96-well plate. Standard and samples are pipetted into wells and ApoE4 present in the sample is bound to the wells by immobilized antibody. Wells are washed and human ApoE4 specific detection antibody is added. After washing away unbound detection antibody, HRP-conjugate is pipetted to the wells. The wells are again washed, a TMB substrate solution is added to the wells, and color develops in proportion to the amount of bound ApoE4. Stop Solution changes the color from blue to yellow, and the intensity of the color is measured at 450 nm. Sensitivity of the kit is 25 ng/ml and detection range is from 50 ng to 800 ng/ml. Recovery inside this range is between 83 and 104% (average recovery is 93%). The intra-assay reproducibility as measured by the coefficient of variation (CV) is < 8 % & inter-assay has CV < 12 %.