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

Your doctor may order this test to help diagnose a medical condition, check how well a treatment is working, or screen for possible health problems. It can also be used to monitor an ongoing condition, investigate symptoms you have been having, or gather more information when earlier test results need a closer look.

Your healthcare provider may recommend this test if you have symptoms like unexplained fatigue, weight changes, swelling, or if they suspect conditions such as infections, allergies, or immune disorders. It can also be used to monitor treatment progress for certain diseases.

Before the test, your care team will explain the procedure and give you instructions to follow. Depending on the type of test, you may need to avoid food or drinks for a set period, pause certain medications, or arrive with a full bladder. Wear comfortable clothing, bring a list of your current medications, and plan to arrive a little early to complete any paperwork.

No special preparation is usually needed, but you may be asked to fast for 8–12 hours if the test involves a specific protein (e.g., albumin). Avoid smoking or caffeine for 30 minutes before the draw. Bring any medications you’re taking.

During the test, a trained technologist or nurse will guide you through each step and answer any questions you have. You may be asked to sit or lie still while equipment is positioned or a sample is collected. Most tests are quick and cause little to no discomfort, though some may involve a brief pinch or a feeling of pressure. Tell the staff right away if you feel pain or become uncomfortable.

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it’s usually over quickly. The blood is then sent to a lab for analysis.

Your results will show whether your values fall within the normal reference range for this test. Normal results usually suggest no signs of the condition being checked, while abnormal results may point to a condition that needs further evaluation. Keep in mind that factors such as medications, diet, and other health conditions can affect results. Your doctor will review the findings with you and explain what they mean for your overall health.

Results are compared to a general range of what’s considered normal for your age and health. High or low levels may point to underlying issues, but they don’t diagnose a condition alone. Your provider will discuss findings with you.