Serological Tests: What They Are, How They Work, and What to Expect

What is a serological test?

A serological test, also known as an antibody test, is a diagnostic test used to detect the presence of antibodies from your blood sample. 

Antibodies are proteins that your immune system makes to protect you from diseases by fighting pathogens (disease-causing germs), such as viruses and bacteria. These tests are important in checking whether your immune system is able to protect you from certain diseases better.

How does the test work?

Serological tests work by measuring the presence and concentration of antibodies in your blood. By detecting these antibodies, serological tests can help determine if you have been previously exposed to a disease, have had a vaccination, or are experiencing an autoimmune response.

These tests are widely used to diagnose and monitor infectious diseases (e.g., HIV, hepatitis, measles, and COVID-19); screen for autoimmune disorders (e.g., rheumatoid arthritis); and assess immunity following vaccination. An antibody serological test can also assess your immune system after a vaccination and check if it is able to protect you against certain diseases better.

You may have specific antibodies in your blood if you:

• Have previously been infected with, or exposed to, a specific pathogen before. Your body would have made antibodies to fight the pathogen and protect you from getting another infection or from having severe symptoms.

• Have had a vaccine against the specific pathogen. The vaccination may protect you by triggering your immune system to make antibodies against the specific pathogen.

However, it's crucial to understand that a serological test measures your body's response to a pathogen rather than diagnosing diseases. 

It also cannot show if the antibodies are from a current or previous infection or vaccination. Finally, it may take weeks for your body to make antibodies after an infection, exposure to a pathogen, or a vaccine.

Why do I need to take a serological test?

Your healthcare provider may recommend you take a serological test to:

• Find out if you've had a recent or past infection.

• Check your vaccination status. If your medical records are incomplete, this test may be necessary to confirm your vaccination status.

• Find out if a vaccine is effective. If you've already been vaccinated against a disease, the test can show if your vaccine is providing enough protection.

• Fulfil a requirement for your school or job. Some organisations may require proof of previous infections or vaccinations.

• Diagnose or monitor autoimmune diseases, such as rheumatoid arthritis and lupus.

• Screen for certain diseases before surgery or during pregnancy

What are the different types of serological tests?

Several types of serologic testing are used to detect different types of antibodies, each with its own method and purpose:

• Agglutination test:

  • It is used to identify antigens in a sample. 

  • The test involves adding a reagent containing antibodies to a suspected material sample. If the sample contains the antigen, the antibodies will bind to it. As a result, the particles clump together, forming an agglutinate complex.

• Enzyme-linked immunosorbent assay (ELISA):

  • ELISA uses an enzyme-coated plate containing specific antibodies to measure the presence of specific antibodies or antigens in a sample. They bind to the antigen or antibody in the sample. 

  • The enzyme produces a measurable colour product when the antigen or antibody binds to the specific antibody.

• Haemagglutination test:

  • It is an antibody blood test used to measure the presence of antibodies in a serum sample. 

  • This test involves mixing the sample with a known amount of red blood cells, which are then incubated. If the sample contains antibodies, they will bind to the red blood cells. This binding causes the red blood cells to clump together.

• Precipitin test:

  • It is used to identify antigens in a sample. 

  • In this test, a reagent containing an antibody is mixed with the sample containing the antigen. If the sample contains the antigen, the antibody will bind to it. Under a microscope, it will also form a visible precipitate.

• Western blot test:

  • Western blot is another type of serological test used to detect the presence of particular proteins in a sample. 

  • It is a more involved process than ELISA and is often used to confirm the diagnosis of certain diseases.

• Immunofluorescence assay (IFA):

  • It uses fluorescent dyes to detect the presence and amount of particular antibodies in a sample. 

  • It is usually used to diagnose autoimmune diseases and is a very sensitive method of detection.

If you are unsure what type of serological test is suitable for you, don’t hesitate to request an appointment with Thomson Medical. Our specialists will help you to answer any questions you have and provide you with tailored recommendations.

How can I prepare for the test?

Most serological tests do not require special preparation. However, your healthcare provider will inform you if you need to fast or avoid certain medications before the test, so do let them know about all prescriptions and over-the-counter (OTC) medications you are taking. This is because certain medications and herbal supplements may increase your risk of bleeding.

For those taking a blood test, you may want to wear loose and comfortable clothing to make it easier for your doctor to access the veins in your arm. Informing your healthcare providers about your needle phobia can also help them prepare you for the procedure. 

Remember to always follow their instructions to ensure accurate results.

What is the procedure like?

A healthcare professional will take a blood sample from a vein in your arm using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. 

The sample is then labelled and sent to the laboratory for analysis. You may feel a slight sting when the needle is inserted. Overall, the procedure usually takes less than five minutes.

What do the results mean?

Your results will depend on which antibodies were measured. You may receive them as titres (antibody levels indicating the strength of your immune response), positive (antibodies to specific pathogens were found), or negative (no antibodies were found).

Common results include:

• Antibodies to a specific pathogen were found. The discovery may mean you were infected before. It could also indicate that you've received a vaccination against a specific disease.

• Low levels of certain antibodies were found. The finding may mean an earlier vaccination does not provide you with enough protection against a disease. It also means you may need a booster shot.

• Autoantibodies were found. Autoantibodies are a type of antibody that attacks healthy cells by mistake. Such antibodies may mean you have an autoimmune disease.

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

What happens after my serological test?

Your doctor will analyse your findings and explain your test results. They will discuss whether you require treatment and the necessary next steps.

The care and treatment provided after serologic testing can vary. Oftentimes, it hinges on the discovery of antibodies. It may also depend on the nature of your immune system's response and its severity. 

An antibiotic or another type of medication may help your body fight the infection. The test results may also show the presence of antibodies related to chronic conditions, such as autoimmune disorders.

If your doctor suspects an infection, they may order another test, even if the first was normal. The bacteria, virus, parasite, or fungus in your body will multiply over time. In response, your immune system will produce more antibodies. This phenomenon makes the antibodies easier to detect as the infection gets worse.

Are there any risks associated with a serological test?

There are minimal risks to blood tests, and they are usually common and safe. You may experience slight pain, bruising, or bleeding at the puncture site. Some people may feel a little lightheaded or dizzy afterwards. 

If you have previously experienced dizziness following blood tests, please inform your healthcare provider. Serious complications are rare.

How much is a serological test?

The cost of a serological test in Singapore varies depending on the specific test and the clinic. For example:

• COVID-19 serological tests typically range from around $32.10 to $90, depending on the clinic and whether record updates are included.

• Routine serological tests for infectious diseases or autoimmune markers (such as hepatitis, HIV, dengue, rheumatoid factor, etc.) generally range from about $10 to $132 per test, based on the type of antibody or antigen being tested.

• Some clinics may charge additional fees for consultation, laboratory procedures, or updates to national records. For example, a COVID-19 serological test with an NIR (National Immunisation Registry) update is priced at $82.

• Comprehensive blood or health screening packages that include serological testing start at about $76 and can go up depending on the range of tests included.

Always check with your chosen clinic for the exact pricing relevant to your needs, as prices may vary and additional fees may apply.

FAQ

What is a serology test for?

A serology test is used to detect antibodies in your blood, helping to diagnose infections, monitor immunity, and screen for autoimmune diseases.

What is the most common serology test?

The ELISA (Enzyme-Linked Immunosorbent Assay) is one of the most commonly used serology tests due to its accuracy and versatility.

What does it mean when a serology test is positive?

A positive result means antibodies were detected, indicating past infection, vaccination, or, rarely, a false positive due to cross-reactivity.

What is the function of serology?

Serology helps assess immune responses, diagnose diseases, monitor treatment, and evaluate immunity after vaccination.

Which disease is best diagnosed by serology?

Serology is particularly useful for diagnosing diseases like HIV, hepatitis, measles, and certain autoimmune conditions.

What happens if a serology test is positive?

Your healthcare provider will interpret the result in context and may recommend further testing or changes to your care plan.

How long does a serology test take?

The blood draw takes only a few minutes. Laboratory analysis may take a few hours to several days, depending on the test.

What is the cost of a serology test?

Costs vary; check with your healthcare provider or hospital for current pricing.

Is a positive antibody test good or bad?

A positive antibody test simply indicates exposure to a pathogen or vaccination. Whether this is good or bad depends on the context and the disease being tested for.

Why is a serology test done before surgery?

Serology tests before surgery help screen for infectious diseases, ensuring patient and staff safety and guiding perioperative care. Serology tests are a vital part of modern medicine, providing essential information about your immune system and helping guide diagnosis and treatment. If you have questions about your tests or results, consult your healthcare provider for personalised advice.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical today.