Serum or plasma concentration of a substance measured by immunoassay (e.g., antibody or protein)

Why Is This Test Done?

Your healthcare provider may order this test to check for abnormal levels of substances in your blood. Common reasons include diagnosing infections, autoimmune disorders, or monitoring conditions like kidney disease, liver disease, or cancer. It can also help evaluate immune responses or detect hidden health issues.

What Does the Test Involve?

A blood sample is drawn from a vein, usually in your arm. The blood is then processed to separate serum or plasma, which is sent to a lab for testing. The immunoassay method detects the target substance with high sensitivity, often using antibodies or other specific reagents.

What Are Common Uses?

This test is frequently used to screen for or confirm conditions such as rheumatoid arthritis (antibodies like rheumatoid factor), infections (e.g., HIV antibodies), or protein abnormalities (e.g., albumin in kidney disease). It may also be part of routine monitoring for chronic illnesses.

What Might Affect Results?

Several factors can influence test results, including recent medications, infections, diet, or dehydration. For example, certain drugs may interfere with antibody detection, and stress or illness can temporarily alter substance levels.