Used to measure glutamic acid decarboxylase (GAD) enzyme activity in human biological samples, primarily in research and clinical settings. Helps in studying autoimmune responses linked to type 1 diabetes, as GAD antibodies are a key marker. Also applied in neuroscience research to investigate GAD's role in producing GABA, a major inhibitory neurotransmitter, aiding studies on neurological disorders such as stiff-person syndrome, epilepsy, and psychiatric conditions. The ELISA format allows for sensitive, quantitative analysis in serum, plasma, or cell culture samples.