The bacterium behind Lyme disease is a corkscrew-shaped spirochete, and it is frequently labelled Gram-negative even though it doesn’t truly fit that group.1Wikipedia. Borrelia burgdorferi It also doesn’t reveal itself on the quick stains labs use for many other infections. That elusiveness is the root of the practical problem: Lyme is usually confirmed not by finding the germ but by finding your body’s response to it, which takes time to appear. So a test result can lag behind the illness, and the rash itself is often the strongest evidence a doctor has.
Is Borrelia Burgdorferi Gram Negative
A Gram stain is a quick lab sorting step. A smear of a sample is dyed, rinsed with a decolorizer, and dyed again, and the color left behind shows how the cell wall holds the dye: purple for Gram-positive bacteria, pink for Gram-negative. Doctors use it mainly to get a fast first look at bacteria that are easy to see and grow, such as in a sample of pus or spinal fluid. It was never designed to diagnose Lyme, and a lab does not order one to check for Lyme disease.
B. burgdorferi has two outer membranes, the feature that gets it called Gram-negative.2Wikipedia. Borrelia burgdorferi But it lacks lipopolysaccharide (LPS), the coating molecule found on the outside of true Gram-negative bacteria.3PubMed Central. Identification of a novel transport system in Borrelia burgdorferi that links the inner and outer membranes Many people use “Gram-negative” as shorthand for “has an LPS outer coat,” and this bacterium breaks that link, so the label misleads. Its surface is instead packed with proteins carrying fat anchors, which help it spread from tick to person and cause disease.4PubMed Central. A Borrelia burgdorferi LptD Homolog is Required for Flipping of Surface Lipoproteins Through the Spirochetal Outer Membrane That makes it unusual even among two-membrane bacteria. Stain results, including Gram, Giemsa and silver stains, depend on how the sample is prepared, and individual spirochetes can look markedly different from one another.5PubMed Central. Morphology of Borrelia burgdorferi: structural patterns of cultured borreliae in relation to staining methods6PubMed Central. Morphology of Borrelia burgdorferi: structural patterns of cultured borreliae in relation to staining methods
The shape itself can change. Under stress, such as antibiotics or poor growing conditions, the corkscrew can roll into a round body form, and round bodies can turn back into moving spirals.7PubMed Central. Destruction of spirochete Borrelia burgdorferi round-body propagules (RBs) by the antibiotic Tigecycline They also carry a different set of surface proteins than the spirals do.8PubMed. Pleomorphic forms of Borrelia burgdorferi induce distinct immune responses Round bodies are not, on their own, proof of a hidden lasting infection.
Why Doctors Rarely Find the Bacterium Directly
The bacterium can be seen in tissue samples, but only rarely in a blood smear.9PubMed Central. Laboratory confirmation of Lyme disease It grows only in a special broth.10PubMed. Evaluation of a new culture medium for Borrelia burgdorferi Batches of that broth vary so much that some need about 100,000 times more bacteria to show growth than others.11PubMed Central. Effects of bovine serum albumin on the ability of Barbour-Stoenner-Kelly medium to detect Borrelia burgdorferi A negative culture therefore doesn’t rule Lyme out. Even in samples from the rash, cultures found the bacterium in only about a quarter to a third of cases.12PubMed Central. A two year prospective study to compare culture and polymerase chain reaction amplification for the detection and diagnosis of Lyme borreliosis
DNA tests do better, depending on where the sample comes from. PCR is a DNA test that looks for the germ’s genetic material. On a skin sample from the rash, a PCR found it in about 8 in 10 patients.13PubMed. Laboratory diagnostic techniques for patients with early Lyme disease associated with erythema migrans: a comparison of different techniques Blood is another story: blood PCR is rarely positive, about 1 in 1,000 blood samples sent to one large lab.14PubMed. Percent positive rate of Lyme real-time polymerase chain reaction in blood, cerebrospinal fluid, synovial fluid, and tissue Joint fluid and tissue samples sent to that lab were positive about 6 in 100 times, the highest of any sample type there.15PubMed. Percent positive rate of Lyme real-time polymerase chain reaction in blood, cerebrospinal fluid, synovial fluid, and tissue A negative blood DNA test means very little and cannot rule Lyme out.
A skin biopsy takes a small punch of skin from the edge of the rash, done under numbing. It isn’t routine, because the rash itself is usually enough, but it may be used when the rash looks unusual.
How the Standard Lyme Blood Test Works
Most Lyme tests look for antibodies, your immune system’s response, not the germ itself.16CDC. Clinical Testing and Diagnosis for Lyme Disease The standard approach is a two-tier test, run in steps on the same blood. The first step is a screening test, and if it is negative, no more testing is done.17CDC. Clinical Testing and Diagnosis for Lyme Disease If the first is positive or unclear (“equivocal”), a second test is run on the same blood.18CDC. Clinical Testing and Diagnosis for Lyme Disease The overall result is positive only when both steps are positive.19CDC. Clinical Testing and Diagnosis for Lyme Disease Your report may list IgM (early antibodies) and IgG (later antibodies).
The older second step is a western blot, a strip that shows bands for antibodies.20CDC. Clinical Testing and Diagnosis for Lyme Disease Blots are complex, hard to interpret and costly.21PubMed Central. Evaluation of Modified 2-Tiered Serodiagnostic Testing Algorithms for Early Lyme Disease So many labs now use a modified version with two screening-type tests instead.22CDC. Clinical Testing and Diagnosis for Lyme Disease In one review, the modified version caught 28% more early infections than the older method.23PubMed Central. Modified Two-Tiered Testing Enzyme Immunoassay Algorithm for Serologic Diagnosis of Lyme Disease
When you read your report, ask which method your lab used. An equivocal first step is not a diagnosis.
Why the Test Can Miss Early Lyme
Antibodies can take several weeks to develop after infection.24CDC. Clinical Testing and Diagnosis for Lyme Disease So blood drawn at the rash stage was positive in only about 4 in 10 patients, and a repeat test weeks later was positive in about two-thirds.25PubMed. Laboratory diagnostic techniques for patients with early Lyme disease associated with erythema migrans: a comparison of different techniques The older two-step test performs well in late Lyme but poorly in early rash cases.26PubMed Central. Evaluation of Modified 2-Tiered Serodiagnostic Testing Algorithms for Early Lyme Disease
A test taken in the first days after a tick bite says nothing about that bite, because the immune system has not yet made antibodies.
The expanding rash is the most common sign of Lyme.27PubMed Central. Evaluation of Modified 2-Tiered Serodiagnostic Testing Algorithms for Early Lyme Disease In areas where Lyme is common, an experienced clinician’s diagnosis of the typical expanding rash is highly accurate, though many Lyme rashes are evenly red rather than bull’s-eye.28PubMed. Laboratory diagnostic techniques for patients with early Lyme disease associated with erythema migrans: a comparison of different techniques If you have the typical rash, ask to be treated without waiting for a test.
Early antibiotics can also keep antibodies from forming, so some treated people never test positive.29Galaxy Diagnostics. Early Lyme Disease Testing: What Clinicians Need to Know A negative test after treatment doesn’t prove you never had Lyme. Success is judged by symptoms, and retesting usually adds little.
What Causes a False Positive Lyme Test
Some Lyme proteins used in tests are also recognised by antibodies made against other germs.30PubMed Central. Antibody Cross-Reactivity in Serodiagnosis of Lyme Disease A shape on one germ can resemble a shape on another, so a test using those shared proteins can read positive even though the person has never met the Lyme bacterium.
False positives can occur with relapsing fever, syphilis, rheumatoid arthritis and Epstein-Barr virus (mono).31CDC. Clinical Testing and Diagnosis for Lyme Disease Cytomegalovirus can cross-react too.32PubMed Central. Antibody Cross-Reactivity in Serodiagnosis of Lyme Disease Rheumatoid factor, an antibody common in rheumatoid arthritis, can bind Lyme proteins.33PubMed Central. Antibody Cross-Reactivity in Serodiagnosis of Lyme Disease The two-step design reduces, though doesn’t eliminate, these errors.34PubMed Central. Antibody Cross-Reactivity in Serodiagnosis of Lyme Disease Overdiagnosis can lead to unneeded strong antibiotics and delay the real diagnosis.35PubMed Central. Antibody Cross-Reactivity in Serodiagnosis of Lyme Disease
If you get a surprising positive, check whether both steps were positive and tell your doctor about any recent mono or autoimmune illness. IgM-only positives months after symptoms deserve caution.
Diagnosing Lyme in the Joints and Nervous System
In Lyme arthritis, DNA testing of fluid drawn from the swollen joint finds the germ in over 3 in 4 cases and helps tell Lyme arthritis from other arthritis.36Emerging Infectious Diseases journal. Current Guidelines, Common Clinical Pitfalls, and Future Directions for Laboratory Diagnosis of Lyme Disease, United States37Emerging Infectious Diseases journal. Current Guidelines, Common Clinical Pitfalls, and Future Directions for Laboratory Diagnosis of Lyme Disease, United States For a swollen knee, a doctor numbs the skin and uses a needle to draw out fluid, a procedure that is also used to relieve swelling. A spinal tap is a similar needle draw under local numbing, done when symptoms point to the nervous system.
Nerve Lyme is harder. DNA testing of spinal fluid found the germ in only 38% of early nerve Lyme cases.38Emerging Infectious Diseases journal. Current Guidelines, Common Clinical Pitfalls, and Future Directions for Laboratory Diagnosis of Lyme Disease, United States But a spinal fluid marker called CXCL13 rises sharply in nerve Lyme.39PubMed. Specificity and Diagnostic Utility of Cerebrospinal Fluid CXCL13 in Lyme Neuroborreliosis In children it correctly flagged about 97% of cases with few false alarms.40PubMed Central. Cerebrospinal fluid CXCL13 as a diagnostic marker of neuroborreliosis in children: a retrospective case-control study Combined with spinal fluid antibody testing, accuracy reached 99% detection and 98% correct negatives.41PubMed. Diagnostic performance of cerebrospinal fluid chemokine CXCL13 and antibodies to the C6-peptide in Lyme neuroborreliosis
Other Tick Infections That Muddy the Picture
The same ticks can carry several germs at once.42Journal of Applied Laboratory Medicine. A Review of Diagnostic Testing and Automation for Lyme Disease So 2% to 20% of Lyme patients, depending on region, also have babesiosis, and up to 10% test positive for anaplasmosis.43Journal of Applied Laboratory Medicine. A Review of Diagnostic Testing and Automation for Lyme Disease The distinction matters because babesiosis needs different treatment than Lyme.44Journal of Applied Laboratory Medicine. A Review of Diagnostic Testing and Automation for Lyme Disease
Each infection needs its own test, since a Lyme antibody test cannot detect babesiosis or anaplasmosis. Coinfection can make the illness look different from typical Lyme, with symptoms that are more intense or more drawn out. Coinfection should be suspected with high fever, anemia, low platelets or poor response to Lyme antibiotics.45PubMed Central. Human Co-Infections between Borrelia burgdorferi s.l. and Other Ixodes-Borne Microorganisms: A Systematic Review
How Fast Ticks Pass On Lyme
In animal studies, half of ticks transmitted infection by about 2 to 3 days of feeding.46Journal of Medical Entomology. Transmission Dynamics of Borrelia burgdorferi s.s. During the Key Third Day of Feeding by Nymphal Ixodes scapularis (Acari: Ixodidae) At 24 hours infection was uncommon, and at 72 hours it was nearly universal.47Journal of Clinical Microbiology. Duration of Tick Attachment and Borrelia burgdorferi Transmission Still, transmission can occur in under 16 hours, and no minimum safe time is proven.48PubMed Central. Lyme borreliosis: a review of data on transmission time after tick attachment So remove ticks promptly and watch for a rash for about a month. Doctors generally advise watching for a rash, fever, or other symptoms over the following weeks rather than testing right away.
Use fine-tipped tweezers and grasp the tick as close to the skin as you can, so you hold the head and mouthparts rather than squeezing the body. Pull steadily upward with even pressure, without twisting or jerking, which can leave mouthparts in the skin. Clean the bite and your hands with soap and water or rubbing alcohol, and write down the date and place of the bite. Testing the tick or yourself right away isn’t useful.
Newer Tests in Development
An experimental urine test detecting a molecule the bacterium sheds found 88% of patients before antibodies appeared.49medRxiv. A direct, urine-based test to diagnose acute Lyme disease using actively secreted peptidoglycan as a biomarker A blood test reading 31 of your own genes identified 90% of early Lyme patients with no false positives.50PubMed Central. A diagnostic classifier for gene expression-based identification of early Lyme disease And a blood protein called CCL19 above about 112 pg/mL a month after treatment flagged most people who went on to lasting symptoms.51PubMed Central. CCL19 as a Chemokine Risk Factor for Posttreatment Lyme Disease Syndrome: a Prospective Clinical Cohort Study These are research results, not tests you can order today, and they still need larger testing.
Some commercial labs advertise tests that claim more. Ask whether a test is FDA-cleared, since unvalidated tests raise the risk of false positives. For now, the CDC two-step approach is the one to stick with.