PCR Test for Lyme Disease: What It Catches and What It Misses

A PCR test for Lyme disease looks for the DNA of Borrelia burgdorferi, the bacteria that causes Lyme, in joint fluid, skin, spinal fluid, or blood. A positive result is highly specific, though lab contamination can cause false positives. A negative result says much less, because Borrelia DNA is often absent from the small sample tested. Joint fluid and skin biopsies perform well, while blood and spinal fluid miss most cases. The CDC’s recommended workup is two-step antibody testing, and PCR sits outside it. If your PCR came back negative and your symptoms still match, that result alone does not rule Lyme out.

Key Takeaways

• PCR finds the bacteria’s genetic material. Standard Lyme tests find your antibodies.
• Joint fluid PCR catches about 73% to 85% of Lyme arthritis cases overall, and up to 96% before long antibiotic courses.
• Blood and spinal fluid PCR miss most infections.
• The CDC’s first-line workup is two-step antibody testing. PCR is an add-on for specific cases.
• A negative PCR leaves Lyme on the table, and a lone positive in late disease deserves a second look.

If you have ever thought, “I tested negative but my symptoms match exactly,” you are far from alone. Our guide to interpreting Lyme test results covers the antibody side.

What a PCR test for Lyme disease looks for

The PCR test for Lyme disease is a DNA test that searches a sample for Borrelia burgdorferi and copies any genetic fragment it finds until the lab can detect it.

Borrelia burgdorferi is the spiral-shaped bacteria that causes most Lyme disease in the United States, carried by blacklegged ticks.

PCR (polymerase chain reaction) is a lab method that makes millions of copies of a specific stretch of DNA, so a trace of genetic material becomes measurable.

Standard Lyme tests are indirect, because they measure the antibodies your immune system makes. A 2016 CDC review describes PCR as able to “provide highly specific evidence of B. burgdorferi nucleic acid.” The same review adds that its usefulness “is limited by low sensitivity (particularly for blood and CSF samples).” Specific means a positive is rarely wrong. Low sensitivity means many true infections test negative.

Which samples can be tested with a Lyme PCR test

Four sample types can go to the lab for Lyme PCR, and each matches a different stage of illness.

• Skin biopsy: a small punch from the edge of the early bullseye rash of Lyme disease.
• Synovial fluid: fluid drawn from a swollen joint, the sample most often paired with Lyme joint pain.
• Cerebrospinal fluid (CSF): the fluid around the brain and spinal cord, collected by lumbar puncture.
• Blood: the easiest sample to collect, and one of the least likely to contain detectable DNA.

Erythema migrans is the expanding red rash at the site of an infected tick bite. The CDC says it appears 3 to 30 days after the bite, about 7 days on average.

Some labs also offer urine PCR. A 2001 meta-analysis found urine assays varied widely between studies, and Borrelia DNA can persist in urine after treatment.

Lyme disease PCR accuracy by sample type

Lyme disease PCR accuracy runs from about 73% to 85% in joint fluid down to 18% to 38% in spinal fluid, depending on the study. This Lyme PCR test accuracy table lists each figure with its source.

Sensitivity is the share of truly infected people a test correctly flags as positive. Specificity is the share of uninfected people a test correctly reads as negative.

The pediatric study followed 124 children at six centers and defined Lyme cases by positive two-tier antibody results. Its authors concluded that PCR did not improve diagnosis. The spinal fluid numbers matter most if you have neurological Lyme symptoms, because a negative CSF PCR is the expected result in most true cases.

Where PCR fits in CDC Lyme testing guidance

The CDC’s standard Lyme workup relies on FDA-cleared, two-step antibody tests, and Lyme PCR has no single validated standard.

The CDC “recommends using antibody tests that have been cleared by the U.S. Food and Drug Administration (FDA) and follow a two-step process.” In the standard version, an enzyme immunoassay (EIA) comes first and a Western blot for Lyme disease confirms it. In the modified two-tier approach, both steps are EIAs.

An EIA (ELISA) is a blood test that screens for antibodies to Lyme bacteria. A Western blot is a follow-up test that sorts those antibodies into bands by protein.

Two-tier testing is the CDC’s two-step antibody approach: a screening test first, then a second test on any positive or unclear result.

The 2016 CDC review states that Lyme PCR “has not been universally standardized.” Dumler’s meta-analysis found published assays differ in methods and gene targets, so one lab’s result may not match another’s.

When a PCR test for Lyme disease is useful

Joint fluid from someone with positive antibody tests is where a PCR test for Lyme disease earns its place.

Lyme arthritis is joint swelling, most often in a knee, caused by Lyme bacteria that have spread beyond the skin.

The 2020 guideline from the Infectious Diseases Society of America, the American Academy of Neurology, and the American College of Rheumatology sets out its advice by sample.

• Joint fluid, antibody positive: the panel recommends PCR on synovial fluid or tissue when treatment decisions need more definitive information.
• Suspected Lyme arthritis in general: the panel favors serum antibody testing first.
• Suspected nervous system Lyme: the panel favors serum antibody testing and advises against routine PCR of CSF or blood.
• Unusual-looking rash: the panel suggests antibody testing, repeated weeks later if negative, over PCR of blood or skin.

Blood PCR also has a narrow role, since the CDC review notes it has helped detect Borrelia mayonii and Borrelia miyamotoi. PCR works differently for Bartonella and Babesia, covered in our guide to co-infection testing.

What a negative PCR test for Lyme disease tells you

A negative PCR test for Lyme disease tells you only that no Borrelia DNA turned up in that sample, on that day.

What a negative PCR means: no Borrelia DNA was found in the sample tested. It does not show that the infection is absent from your body.

Treatment history matters too. In a 1994 NEJM study, joint fluid PCR was positive in 96% of patients who were untreated or had only short oral courses. It was positive in only 37% of those given IV or month-long oral antibiotics. Our guide to a false negative Lyme test explains other reasons results miss.

Positive results need the same care. A review in Clinical Microbiology Reviews says PCR should not be the only lab evidence for Lyme beyond the skin. It adds that a positive PCR with negative antibody tests in late Lyme most likely reflects a false positive.

PCR vs Western blot and two-tier antibody testing

Western blot testing and PCR answer different questions: PCR asks whether bacterial DNA is present, and the Western blot asks whether your immune system has responded.

The antibody figures come from the 2016 CDC review of Lyme lab testing. Antibody timing explains why an early ELISA test for Lyme disease can come back negative.

What to do after a negative Lyme PCR

Your next step after a negative Lyme PCR is to read that single result alongside your antibody tests, exposure history, and symptoms.

1. Ask which sample was tested. A negative blood or CSF PCR carries far less weight than a joint fluid result.
2. Check your timing. Note when symptoms began and whether you took antibiotics before the sample.
3. Pair it with two-tier antibody testing. The CDC notes FDA-cleared antibody tests have good sensitivity after 4 to 6 weeks.
4. Write down your exposure history. Tick bites, rashes, and travel shape how results are read.
5. Work with a clinician who reads results in context. A Lyme disease specialist weighs labs alongside your full picture.

A negative result is one data point, and a clinician can read it next to your antibody tests, timeline, and exposure history. My Lyme Doc sees patients by telehealth in 11 states, with an office in Centennial, Colorado. You can book a consultation with Dr. Mueller to review your results together.