Lyme disease doesn’t produce a single dramatic lab result that clinches the diagnosis. Instead, the picture is built from antibody tests, and in some cases, subtle shifts in routine bloodwork that point toward infection or rule out other causes. The primary lab abnormality is a positive two-tier antibody test, but several other markers can be affected depending on how far the infection has progressed.
The Two-Tier Antibody Test
The cornerstone of Lyme diagnosis is a two-step blood test that detects antibodies your immune system produces against the Lyme bacterium. The first step is an enzyme immunoassay (EIA), sometimes called an ELISA. If that result comes back positive or borderline, a second test is performed on the same blood sample. In the standard approach, the second test is a Western blot. A newer modified approach uses two different EIA tests instead. The overall result is only considered positive when both steps are positive.
These tests measure two types of antibodies: IgM and IgG. IgM antibodies appear first, typically within the first few weeks of infection. IgG antibodies develop later and persist longer. One important detail: a positive IgM result is only considered meaningful if you’ve been sick for 30 days or less. After that window, IgM results are disregarded because they’re more likely to be a false positive. Only IgG matters in longer-duration illness.
The biggest limitation is timing. In the earliest days of infection, before your immune system has ramped up antibody production, both tests can come back negative even though you’re infected. If you were bitten recently and have a bull’s-eye rash, your doctor may start treatment based on symptoms alone and skip or delay testing.
What Routine Blood Work Shows
A standard complete blood count (CBC) in Lyme disease is often surprisingly normal. White blood cell counts can be normal or mildly elevated, which isn’t particularly helpful for distinguishing Lyme from other infections. What’s more telling is when certain counts are low. If your white blood cells or platelets drop below normal, that pattern suggests you may be dealing with a co-infection like ehrlichiosis or babesiosis, both of which are also transmitted by ticks and can occur alongside Lyme.
General inflammatory markers like sed rate (ESR) and C-reactive protein (CRP) can be elevated in Lyme disease, particularly with joint involvement, but they’re nonspecific. Plenty of Lyme patients have normal inflammatory markers, so a normal result doesn’t rule anything out. These tests are more useful for tracking the body’s overall inflammatory response than for diagnosing Lyme specifically.
Liver Function Tests
Mild elevations in liver enzymes are one of the more common incidental findings in early Lyme disease. These are often caught on a routine metabolic panel and can be the first hint that something beyond a simple viral illness is going on. The elevations are typically modest and resolve with treatment. They reflect low-grade liver inflammation caused by the Lyme bacterium circulating through the bloodstream early in infection.
Spinal Fluid Abnormalities in Neurological Lyme
When Lyme disease affects the nervous system, a condition called neuroborreliosis, a spinal tap reveals a characteristic pattern. The fluid shows an elevated white blood cell count with a predominance of lymphocytes, a type of immune cell. Protein levels in the spinal fluid are mildly elevated. Glucose levels, notably, stay normal. This combination helps distinguish Lyme meningitis from bacterial meningitis, where glucose typically drops.
Spinal fluid isn’t tested routinely. It’s only collected when someone develops neurological symptoms like facial paralysis, severe headaches with neck stiffness, or nerve pain that suggests the infection has crossed into the central nervous system.
Muscle Enzyme Elevations
In rare cases, Lyme disease causes muscle inflammation (myositis), which shows up as elevated creatine kinase (CK) on blood work. This enzyme leaks out of damaged muscle cells. Documented cases have shown CK levels rising dramatically over the course of weeks. Muscle pain and fatigue are among the most common complaints in Lyme patients, and some researchers believe primary muscle involvement may be underrecognized because those symptoms overlap with so many other conditions.
Kidney Markers
Kidney involvement in Lyme disease is uncommon, but it has been documented. In reported cases, urinalysis showed blood and protein in the urine, along with abnormal red blood cells that indicate the problem originates in the kidney’s filtering units rather than somewhere else in the urinary tract. Some patients developed significant kidney impairment with elevated creatinine levels and heavy protein loss. These cases are rare enough to be published individually in medical literature, so kidney abnormalities are not something most Lyme patients will encounter.
What Can Cause a False Positive
Because the first-tier antibody test detects immune activity rather than the bacterium itself, several other conditions can trigger a positive result in someone who doesn’t have Lyme. Syphilis is a well-known cause because the bacterium is a close relative of the Lyme organism, and antibodies can cross-react. Mononucleosis (caused by Epstein-Barr virus), periodontal disease, rheumatoid arthritis, and lupus can also produce false positives. This is exactly why the two-tier system exists: the second test is designed to weed out these cross-reactions and confirm that the antibodies are truly targeting the Lyme bacterium.
If you’ve been told your Lyme test was positive but your symptoms don’t fit, or if you have one of these other conditions, it’s worth discussing false-positive possibilities with your provider. A single positive screening test without confirmation from the second step is not a reliable diagnosis.
Timing Matters More Than Any Single Lab
The most important thing to understand about Lyme labs is that their accuracy depends heavily on when they’re drawn. Testing too early, within the first week or two of a tick bite, catches many people before their immune system has produced detectable antibodies. Testing too late with only IgM results can produce misleading positives. Routine bloodwork like a CBC or liver panel may show only subtle changes that don’t point clearly to Lyme without clinical context. The diagnosis almost always depends on combining lab results with your symptoms, exposure history, and where you live or have traveled.