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What is Serology?

What Are Serologic Tests?

Serologic tests are blood tests that look for antibodies in your blood. They can involve a number of laboratory techniques. Different types of serologic tests can diagnose various disease conditions. Serologic tests have one thing in common. They all focus on proteins made by your immune system. This vital body system helps keep you healthy by destroying foreign invaders that can make you ill. The process for having the test is the same regardless of which technique the laboratory uses during serologic testing.

Why Do I Need a Serologic Test?

To understand serologic tests and why they’re useful, it’s helpful to know a little about the immune system and why we get sick.

Antigens are substances that provoke a response from the immune system. They are most often too small to see with the naked eye. They can enter the human body through the mouth, through broken skin, or through the nasal passages. Antigens that commonly affect people include the following:

  • bacteria
  • fungi
  • viruses
  • parasites

The immune system defends against antigens by producing antibodies. These antibodies are particles that attach to the antigens and deactivate them. When your doctor tests your blood, they can identify the type of antibodies and antigens that are in your blood sample and identify the type of infection you have.

Sometimes the body mistakes its own healthy tissue for outside invaders and produces unnecessary antibodies. This is known as an autoimmune disorder. Serologic testing can detect these antibodies to help your doctor diagnose an autoimmune disorder.

What Happens During a Serologic Test?

A blood sample is all that the laboratory needs to conduct serologic testing.

The test will occur in your doctor’s office. Your doctor will insert a needle into your vein and collect blood for a sample. The doctor may simply pierce the skin with a lancet if conducting serologic testing on a young child.

The testing procedure is very quick. The pain level for most people isn’t severe. Excessive bleeding and infection may occur, but the risk of either of these is very low.

What Are the Types of Serologic Tests?

Because antibodies are so diverse, various tests are useful for detecting the presence of different types:

  • An agglutination assay shows whether antibodies exposed to certain antigens will cause particle clumping.
  • A precipitation test shows whether the antigens are similar by measuring for the presence of antibody in body fluids.
  • The Western blot test identifies the presence of antimicrobial antibodies in your blood by their reaction with target antigens.

What Do the Results Mean?

Normal Test Results

Your body produces antibodies in response to antigens. If testing shows no antibodies, it indicates you don’t have a current or past infection. Results that show there are no antibodies in the blood sample are normal.

Abnormal Test Results

Antibodies in the blood sample often mean you’ve had an immune system response to a specific antigen from either a current or a past exposure to a disease or foreign protein.

The testing may also diagnose an autoimmune disorder. In that case, antibodies to normal or non-foreign proteins or antigens would be present in the blood.

The presence of certain types of antibodies can also mean that you’re immune to one or more antigen. This means that future exposure to the antigen or antigens won’t result in illness.

Serologic testing can diagnose multiple illnesses, including:

  • brucellosis, which is caused by bacteria
  • amebiasis, which is caused by a parasite
  • measles, which is caused by a virus
  • rubella, which is caused by a virus
  • HIV
  • syphilis
  • fungal infections

What Happens After Serologic Testing?

The care and treatment provided after serologic testing can vary. It often depends on whether antibodies were found. It may also depend on the nature of your immune response and its severity.

An antibiotic or another type of medication may help your body fight the infection. Even if your results were normal, your doctor might order an additional test if they still think you might have a specific type of infection.

The bacteria, virus, parasite, or fungus in your body will multiply over time. In response, your immune system will produce more antibodies. This makes them easier to detect as time goes on and the infection gets worse.

The tests results may also show the presence of antibodies related to chronic conditions, such autoimmune disorders.

Your doctor will explain your test results and what the next steps will be.

Content licensed from:

Written by: Krista O'Connell
Medically reviewed on: Dec 08, 2015: Steven Kim, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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