Plasma levels refer to the concentration of various substances (such as hormones, drugs, or proteins) present in the blood plasma of an individual. These levels can be measured through blood tests and are important for assessing the overall health of an individual, diagnosing diseases, monitoring treatment responses, and evaluating the effectiveness of medications. Abnormal plasma levels of certain substances can indicate underlying health issues or imbalances in the body's system, making it crucial for healthcare professionals to regularly monitor and interpret these levels in their patients.