Serum/plasma mass concentration of immunoglobulin G (IgG) antibodies against a specific antigen (likely a pathogen or vaccine component)

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms of an infection, if you’ve been exposed to a specific pathogen (like a virus or bacteria), or if you’ve received a vaccine. It can also be used to monitor immune function in certain conditions, such as chronic illnesses or after vaccination.

What to Expect Before the Test

No special preparation is usually needed. You may have a small needle inserted into your arm to draw blood. If you’re taking blood from a vein in your arm, you might feel a slight pinch, but it’s typically over quickly. If you’re concerned about needles, let your healthcare provider know.

What the Test Results Mean

Results show the level of specific antibodies in your blood. Higher levels may indicate a strong immune response to a vaccine or past infection. Lower levels might suggest a weaker response or reduced immunity. Your provider will interpret the results in the context of your health and symptoms.

Common Reasons for Testing

This test is often used to confirm exposure to certain diseases (like measles, rubella, or COVID-19), check if a vaccine worked, or evaluate immune function in people with weakened immune systems.