Apolipoprotein E (ApoE) is a 34kDa 299 amino acid single chain plasma glycoprotein with three allelic isoforms that differ by a single amino acid. ApoE mediates the binding of very low density lipoproteins, high density lipoproteins, and chylomicrons to the low density lipoprotein (LDL) receptor, LDL receptor related protein, and heparan sulfate proteoglycans. Decreased serum ApoE levels are associated with higher risk of Alzheimer’s disease. The sensitive quantitative measurement of total human ApoE antigen in plasma and serum is easily performed with this 96 well strip format ELISA kit. ApoE in normal human serum ranges from 16-169 µg/ml with an average concentration of 47 µg/ml. The assay measures total human ApoE in the 0.2-20 ng/ml range. Samples giving human ApoE levels above 20 ng/ml should be diluted in diluent before use. A 1:100,000 to 1:200,000 dilution for normal human plasma is suggested for best results. Human ApoE will bind to the affinity purified capture antibody coated on the microtiter plate. After appropriate washing steps, biotinylated anti-human ApoE primary antibody binds to the captured protein. Excess primary antibody is washed away and bound antibody is reacted with the peroxidase conjugated streptavidin. Following an additional washing step, TMB substrate is used for color development at 450nm. A standard calibration curve is prepared along with the samples to be measured using dilutions of human ApoE. Color development is proportional to the concentration of total ApoE antigen in the samples. All reagents and standards are provided in these ELISA kits.