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Harvard Health Publishing, Harvard Medical School

Diagnosis and Testing

Making a diagnosis is a lot like solving a mystery. Like detectives, doctors collect and connect clues, call upon their knowledge and experience, and gather hard evidence to determine the likeliest explanation for a given problem — or set of symptoms.

When a Lyme disease diagnosis is simple

Doctor talking to patient
Tell your doctor right away if you were bitten by a tick, or if you are are experiencing symptoms and have other risk factors for Lyme disease (such as spending time in an area where Lyme disease is common).
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A person who notices a tick bite and gets a bullseye rash will typically get a Lyme disease diagnosis. Treatment can start right away without any testing.

Another straightforward example would be a person who has spent time outdoors in an area where Lyme disease is common. Let’s say that person doesn’t have a bullseye rash but has other possible symptoms of Lyme disease. Their doctor does a standard two-step blood test, and both are positive. In this case the person gets a Lyme disease diagnosis and starts treatment.

When a Lyme disease diagnosis is tricky

There are several reasons it can be hard to diagnose Lyme disease.

  • Tests are less accurate for a short period of time after you first become infected. That’s because Lyme disease tests look for proteins created by your immune system to help you fight off infection (antibodies), rather than for the infection itself, and it can take a few weeks for your body to make enough antibodies to cause a positive test.

  • The only sure sign of Lyme disease is an erythema migrans (EM) rash, which often has a bullseye shape. But up to 30% of people who get Lyme disease never get a rash. It is also possible that a person may not notice a rash before it goes away.

  • Symptoms of Lyme disease like fever and body aches can also be caused by other illnesses. This may result in Lyme diagnoses being missed because symptoms are attributed to another illness.

  • Using today’s tests, it is difficult to distinguish between an old Lyme disease infection and a new one.

That’s why Lyme disease cases may be missed, and as many as 40% of Lyme disease cases are not diagnosed until a later stage of the disease. By that time, Lyme disease is harder to treat, and long-term complications are more likely, so an early, accurate diagnosis is very important.

How is Lyme disease diagnosed?

An EM rash is a sure sign of Lyme disease, so your doctor can diagnose and treat you without the need for laboratory tests.

An Erythema Migrans (EM) rash that's shaped like a bullseye
Subtle Erythema Migrans (EM) rash, shown on person with darker skin
An EM rash, often shaped like a bullseye (left), is a sure sign of Lyme disease. If you develop an EM rash, you should be diagnosed & treated for Lyme disease without the need for further lab tests. EM rashes are not as obvious on darker skin (right).
Getty Images (left), CDC (right)

For all other cases, your doctor should consider whether your symptoms and risk factors point to a Lyme disease diagnosis. For example:

  • Were you bitten by a tick?

  • Did you spend time outdoors in an area where Lyme disease is common?

  • Recent travel: Lyme disease may be common where you were, even if it is unusual where you live.

  • Your current symptoms and how long have they been present.

  • Your full medical history, including previous unexplained symptoms that may help lead to an accurate diagnosis — whether that ends up being Lyme disease or another condition.

"My doctor diagnosed me based on my rash and other symptoms, and my recent travel to an area with Lyme disease."

Lyme Disease Patient Experience Survey Respondent

Female, 40, Chicago, IL

Do I need a Lyme disease test?

Your doctor will consider whether your symptoms and risk factors suggest Lyme disease when deciding whether you need a Lyme disease test. Laboratory tests can support a clinical diagnosis, but should not be used on their own to confirm or rule out a current Lyme disease diagnosis.

Your doctor may also do tests to see if other conditions with similar or overlapping symptoms — for example, thyroid disease, autoimmune disease, or other tick-borne diseases — could be causing your symptoms. If you have been traveling, your doctor might test you for species of Borrelia that cause Lyme disease in other parts of the world.

If you think you may have Lyme disease, but your doctor hasn’t considered it or has ruled it out before testing you for it, here’s how you can start a conversation: Give your doctor a list of Lyme disease symptoms and risk factors , and ask them if, given your own symptoms and risk factors, Lyme disease could be a possible cause and whether you should be tested.

In some cases, a Lyme disease test may not be helpful. Using today’s tests it is difficult to distinguish between current and previous infections, so if you were previously diagnosed with Lyme disease and may have been re-infected, your doctor should make the diagnosis based on your symptoms and risk factors.

Tick Testing

If you saved the tick that bit you, you can send it to a lab to see if it was carrying any pathogens. A tick may be positive for certain disease-causing pathogens but may not have passed any of them on to you. Still, the information may help your doctor decide which tick-borne infections to test you for. Do not delay preventive antibiotics after a high-risk tick bite while you await the results of a tick test.

To find a lab that tests ticks, you can call your local health department, or find one through the University of Rhode Island’s TickEncounter website. Tests generally range from $35 to $100 and are not covered by insurance.

How will my doctor test me for Lyme disease?

Person wearing medical exam glove holding a vile that's labeled Lyme test
The CDC recommends two-step blood testing, sometimes called a two-tiered test, to diagnose Lyme disease.
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The CDC recommends two-step testing, sometimes referred to as a two-tiered test, for Lyme disease. You will need to go to a lab to have blood drawn. It takes a few days to get results.

If the first test comes back positive or unclear, the lab will do the second blood test. If the first test comes back negative, the CDC does not recommend the second test. However, according to the CDC the second test must be positive for you to be diagnosed with Lyme disease.

The first test: ELISA (enzyme-linked immunosorbent assay)

This blood test is for antibodies against the Lyme disease bacteria. Because it can take some time for your body to produce antibodies, this test isn’t always accurate soon after a person is infected.

The second test: Western Blot or a second ELISA

There are two options for the second test. One is called a Western blot, which looks at how your antibodies react to specific parts of the Lyme disease bacteria. The Western blot test has been part of the two-step testing system since 1994 and is more commonly used.

The other option is to do a second ELISA test, which measures antibodies to a specific protein found on Lyme disease bacteria. Because these tests are newer, not all doctors have experience with them and not all labs have access to them.

These tests can be run on the blood sample used for the first test. You should not need to go back to the lab.

A possible drawback of the two-step testing system

The CDC testing guidelines recommend a second test only if the first test is positive or unclear. Because the first test may not pick up antibodies soon after possible exposure to the Lyme disease bacteria, that means a person with Lyme disease may never get the second test. So, if your ELISA test is negative, you may want to ask your doctor to repeat the test in two to four weeks, or to get another sample of your blood for testing a week or so later.

Which second test is best: ELISA or Western blot?

A second ELISA test is more sensitive (less likely to miss an existing infection) during the earlier stages of Lyme disease. If you think you were infected in the past several weeks or months, you can ask your doctor to consider using a second ELISA test.

A second ELISA and a Western blot are considered equally sensitive in people who were infected months or years earlier. Some doctors prefer using the Western blot for suspected late-stage cases because it can provide additional information to help determine if you have Lyme disease. (For more information, see What do my test results mean?)

What do my test results mean?

If both tests come back positive, that means you have had Lyme disease at some point in time. (If you were previously diagnosed with Lyme disease and could have been reinfected, a positive Lyme disease test may not be helpful because it is difficult to distinguish between current and previous infections using currently available tests.)

If either or both of your tests come back negative, your doctor may still diagnose Lyme disease, particularly if you recently developed Lyme-like symptoms, regardless of your test results. But, if your doctor does not diagnose you with Lyme disease, you can ask to be re-tested in a few weeks. If you do have Lyme disease, your body may build up sufficient antibodies by that point to be detected by a blood test.

Two-step blood testing for later stages of Lyme disease is more accurate than for early infection because your body should have had sufficient time to produce the antibodies detected by diagnostic tests.

Interpreting the Western blot test

The Western blot test looks at whether you have an immune response — the production of IgM or IgG antibodies — to specific proteins (antigens) on the Lyme disease bacteria. IgM antibodies are usually made by your body when the infection is new and recent, while IgG antibodies are usually made some weeks later. When the IgM or IgG antibodies combine with specific proteins from the Lyme disease bacteria, this produces dark spots, or “bands” on the Western blot test strip.

The CDC considers a Western blot test to be positive for Lyme disease if at least two of three IgM bands are positive within 30 days of symptom onset, or five of 10 IgG bands are positive at any time.

This means that if you have three or four positive IgG bands, your test will be considered negative by CDC criteria. Some doctors may diagnose and treat you if you have fewer than the required number of positive IgM or IgG bands, because you do still demonstrate some antibody response against the Lyme disease bacteria. Others may not.

Graphic explaining the Western blot test
On a Western blot test, antibodies that your body has made against the Lyme disease bacteria combine with specific proteins on the Lyme disease bacteria to create dark spots, or "bands." The test strips pictured here are positive by CDC criteria.

If your Western blot test comes back negative, ask your doctor:

  • Did I have any positive bands on the test?

  • If so, ask if the positive bands on the Western blot, along with your symptoms and risk factors, suggest that you could have Lyme disease.

Lyme disease test results can vary depending on the stage of illness, how well your immune system responds to the Lyme disease bacteria, and even which lab performs the test (see Sidebar, “Does it matter which lab my doctor uses?”).

Does it matter which lab my doctor uses?

Some labs report on antibody bands that are not included in standard two-step tests. They may also use their own criteria, which is different from criteria used by the CDC, for interpreting test results.

Other labs use tests, such as urine or other kinds of blood tests, that have limited or uncertain value. Because it is unclear how helpful these tests may be, they are not currently recommended.

Diagnosing and testing for possible later-stage Lyme disease

A doctor examining a patient's leg while the patient is talking
Doctors may not immediately suspect Lyme disease, especially at a later stage. If you think you may have Lyme disease, talk to your doctor about your symptoms and risk factors, and ask if Lyme disease could be the cause.
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Your doctor may not immediately suspect Lyme disease if your condition has progressed to a later stage. For one thing, many symptoms of later-stage Lyme disease are nonspecific, meaning that they may be caused by several different conditions. In addition, current symptoms may be more difficult to connect to historical risk factors (for example, a hazily recalled tick bite or trip to a Lyme disease-endemic area).

If your doctor does not consider Lyme disease, you can raise the possibility of being tested for it based on how your symptoms and risk factors compare to those of Lyme disease. You’ll start with a standard two-step blood test.

Your doctor may also recommend additional diagnostic tests depending on your symptoms. For example, if you have joint pain and swelling, your doctor may check your synovial fluid (the fluid located in your joints) for Lyme disease bacteria. If you have neurological symptoms, your doctor may consider a spinal tap. However, these tests are used infrequently. They are not always accurate, and a spinal tap is invasive. If you have neurological symptoms, your doctor may do brain imaging or nerve conduction studies. These tests cannot diagnose Lyme disease, but they can give your doctor more information to help them confirm or rule out a diagnosis.

What is on the horizon for Lyme testing?

A scientist looking into a microscope
Researchers are studying new ways to diagnose Lyme disease including better antibody tests, direct detection methods, and different methods to measure immune response.
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Because Lyme bacteria (Borrelia) are not usually present in high enough numbers to be detectable, blood tests to look for Borrelia are not helpful.

Better diagnostic tests are needed that are direct and can detect infection at all stages of Lyme disease. Researchers are studying new diagnostic methods using better antibody tests, direct detection methods, and different ways to measure immune response to Lyme disease.