Used in biomedical research to quantify levels of apolipoprotein A4 in human plasma or serum samples. Enables studies on lipid metabolism, cardiovascular disease risk assessment, and metabolic disorders. Commonly applied in clinical laboratories and research settings to investigate the role of Apo-A4 in atherosclerosis, insulin resistance, and HDL function. Supports development of diagnostic methods and evaluation of therapeutic interventions targeting lipid-related pathways.