The ADA Serum test measures the level of the Adenosine Deaminase enzyme in your bloodstream. While the 'Body Fluid' test is specific for localized infections, the serum test provides a broader look at your immune system's activity. Elevated levels in the blood can be associated with conditions that involve high immune cell activation, such as certain infections or autoimmune disorders. This simple blood test serves as a key diagnostic clue, helping your doctor investigate the root cause of systemic inflammation or immune response.