The Omega-3 index is a blood test that measures the amount of omega-3 fatty acids (EPA and DHA) in the red blood cells (RBC) membranes. Omega-3 fatty acids are essential fats – the body can’t make them but must get them from foods or supplements. People with low omega-3 levels have a 10-fold higher risk for sudden cardiac death compared to people with high omega-3 status.