Can Lyme Disease Cause a Low White Blood Cell Count?

Lyme disease can lower certain types of white blood cells, though the picture is more subtle than a simple yes or no. In early, untreated Lyme disease, overall white blood cell counts often remain in the normal range, but the mix of cells shifts: lymphocytes drop, sometimes below normal thresholds, while monocytes and neutrophils tend to rise. That shift can show up on routine blood work and raise questions, especially when co-infections carried by the same ticks push counts even lower.

How Lyme Disease Reshapes White Blood Cells

A 2024 study comparing 236 people with early, untreated Lyme disease to 61 healthy controls found that the total white blood cell count barely budged. The median change from pre-infection levels was under four percent, which was not statistically meaningful. What did change was the composition. Lymphocytes dropped by about 14 percent from pre-infection values, while monocytes rose by roughly 25 percent. Neutrophils trended upward too, though that shift was less consistent across patients.¹

So if you get a standard blood panel during a Lyme infection, the top-line white blood cell number might look perfectly fine. The changes hide inside the differential, the breakdown of which types of white cells are circulating. A doctor who only glances at the total count could miss the pattern entirely. This is one reason Lyme disease is not usually diagnosed through blood counts alone. The classic erythema migrans rash, exposure history, and serologic testing carry the diagnostic weight.

The lymphocyte drop makes biological sense. Borrelia burgdorferi, the bacterium behind most Lyme disease, triggers an immune response that redirects lymphocytes to the site of infection and can also suppress certain lymphocyte populations as part of the pathogen’s strategy for evading the immune system.² Meanwhile, monocytes and neutrophils ramp up because these are the frontline cells that respond to bacterial invaders. The result is a white cell count that looks normal in aggregate but is quietly reorganized underneath.

Men and Women Respond Differently

One of the more surprising findings from that same 2024 study is that men with early Lyme disease were considerably more likely than women to develop true lymphopenia, meaning lymphocyte counts that dip below the standard clinical cutoff. About 32 percent of men with early Lyme disease had lymphopenia, compared to roughly 20 percent of women. Among the healthy controls, there was no such sex difference.¹

The researchers noted that sex-based differences in immune response are well documented across many infections and autoimmune conditions. Women generally mount stronger adaptive immune responses, which may explain why their lymphocyte counts hold up better during the acute phase of Lyme disease. For men, the takeaway is practical: a low lymphocyte count during tick season, especially alongside a rash or flu-like symptoms, is worth mentioning to your doctor even if the total white blood cell number appears unremarkable.

Blood Cell Changes in Children With Lyme Disease

Lyme disease in children follows a somewhat different blood count pattern depending on which form the disease takes. A 15-year study of children with Lyme disease in Switzerland found that outright leukopenia, a total white blood cell count that drops below the normal range, occurred in only about 2.5 percent of pediatric patients overall. The distribution was uneven, though. None of the children with skin-only manifestations had leukopenia, while about 3.5 percent of those with Lyme neuroborreliosis, the form that affects the nervous system, did.³

Interestingly, children with Lyme arthritis showed the opposite trend: their white blood cell counts, including neutrophils and monocytes, were significantly higher than in children with skin disease or neuroborreliosis.³ Lyme arthritis involves intense joint inflammation, and the body floods the area with immune cells, pushing counts upward. If your child’s blood work shows elevated white cells alongside a swollen knee after time spent outdoors in an endemic area, Lyme arthritis should be on the differential even though the white count is high rather than low.

When the Count Really Crashes, Look Beyond Lyme

A mildly low lymphocyte count is one thing. A dramatic drop across multiple cell types, including red cells and platelets, is another. In rare cases, Lyme disease itself has been linked to pancytopenia, where all major blood cell lines fall at once. A published case report described a patient with confirmed Borrelia infection who developed low counts across white cells, red cells, and platelets simultaneously.⁴ That kind of presentation is unusual enough to warrant its own case write-up, which tells you how rarely it happens.

Far more often, severely low white blood cell counts in someone with a recent tick bite point toward a co-infection rather than Lyme disease alone. Two tick-borne pathogens deserve special attention here.

Babesiosis

Babesia species are parasites that infect red blood cells and are transmitted by the same Ixodes ticks that carry Borrelia. Babesiosis is well known for causing blood abnormalities that go well beyond what Lyme typically produces. Patients can develop hemolytic anemia, where red blood cells are destroyed faster than the body replaces them, along with neutropenia and thrombocytopenia. In severe cases, babesiosis can trigger pancytopenia or even disseminated intravascular coagulopathy, a dangerous clotting disorder.⁵ If your blood work shows deeply low counts across multiple cell lines after a tick bite, babesiosis should be ruled out, particularly in the northeastern United States where both pathogens circulate in the same tick populations.

Borrelia miyamotoi

This is a lesser-known relative of the Lyme disease bacterium, also transmitted by Ixodes ticks, that causes a relapsing fever-like illness rather than the classic Lyme rash. A case series from the northeastern United States found that neutropenia and thrombocytopenia were common among patients with Borrelia miyamotoi disease, along with elevated liver enzymes.⁶ Because standard Lyme serologic testing does not detect Borrelia miyamotoi, a patient with a tick bite, fever, and low blood counts might test negative for Lyme while actually carrying this closely related infection. It is an easy diagnosis to miss unless the clinician specifically considers it.

How Often Are Co-infections Actually Behind Abnormal Counts?

The fear of co-infection is reasonable, but the actual frequency depends on geography. A European study specifically set out to determine whether patients with the classic Lyme rash (erythema migrans) who also had low white cell counts or low platelets were secretly co-infected with Anaplasma phagocytophilum or tick-borne encephalitis virus. Among 67 such patients, not a single co-infection was identified. The researchers concluded that in European endemic areas, co-infection is rare among patients who present with the typical skin lesion of early Lyme disease.⁷

The picture may differ in North America, where babesiosis is more common and the mix of tick-borne pathogens varies by region. In parts of the upper Midwest and New England, co-infection rates with Babesia and Anaplasma are higher than in most of Europe. The practical point is that geography matters. A low white cell count alongside a Lyme diagnosis in Connecticut raises different diagnostic questions than the same finding in southern Germany.

Can Lyme Treatment Itself Lower Your White Blood Cells?

This is a question that catches many patients off guard. The standard first-line treatment for Lyme disease is doxycycline, a tetracycline antibiotic. Doxycycline is generally considered one of the safest antibiotics available, but there are rare reports of it causing neutropenia, a specific drop in neutrophils. A case report documented recurrent severe neutropenia in a young, otherwise healthy woman each time she was exposed to doxycycline. Her neutrophil counts recovered after the drug was stopped and improved further with a medication that stimulates white cell production.⁸

Among tetracycline antibiotics, doxycycline appears to be one of the least likely to cause neutropenia.⁸ The proposed mechanisms involve either immune-mediated destruction of developing white cells in the bone marrow or a direct suppressive effect on cell production. Either way, it is rare enough that you should not avoid doxycycline out of fear of low counts. But if you are on doxycycline for Lyme and your blood work shows a new drop in neutrophils, the medication itself is worth considering as a cause, especially if the timing lines up with when you started the drug.

Reading Your Blood Work After a Tick Bite

If you have had a tick bite and are looking at a complete blood count report, here is what the Lyme-related pattern tends to look like during acute infection:

Total WBC: Usually normal or near-normal. A dramatically low total count is more suggestive of co-infection or another cause.
Lymphocytes: Often mildly decreased, sometimes dipping below the normal range. This is the most consistent white cell change in early Lyme.
Monocytes: Tend to rise, sometimes above normal thresholds. A monocyte bump alongside a lymphocyte dip is a pattern seen in several bacterial infections, not just Lyme.
Neutrophils: May be slightly elevated, though the change is less reliable than the lymphocyte drop.
Platelets: Usually stay in the normal range in uncomplicated Lyme disease. A significant platelet drop should trigger consideration of babesiosis or anaplasmosis.

None of these changes are specific enough to diagnose Lyme disease on their own. A low lymphocyte count can show up with viral infections, stress, corticosteroid use, and many other conditions. The value of checking blood counts during suspected Lyme disease is less about confirming the diagnosis and more about catching complications or co-infections that might change the treatment approach. If your white blood cell differential looks off after a tick bite, it gives your doctor one more piece of the puzzle rather than a standalone answer.

Why Blood Counts Alone Are Poor Diagnostic Tools for Lyme

It is tempting to think of a blood test as a straightforward way to screen for Lyme disease, but the changes in white blood cell counts during early Lyme are too variable and too nonspecific to serve that purpose. Many patients with confirmed Lyme disease have completely normal blood counts. Others have shifts that overlap with what happens during a common cold or a bout of stress. The 2024 study that documented the lymphocyte-monocyte shift was analyzing group-level trends across hundreds of patients. For any individual, the overlap between “infected” and “healthy” blood counts is large.¹

Serologic testing, the two-tier system of antibody tests, remains the standard method for laboratory confirmation of Lyme disease. Even that has well-known limitations in the first couple of weeks of infection, before antibodies have had time to develop. The clinical diagnosis still hinges on the erythema migrans rash when it is present, since roughly 70 to 80 percent of Lyme patients develop one. In the absence of a rash, the combination of exposure history, symptoms, and serologic results is what clinicians rely on. Blood counts are best thought of as supporting information, helpful for flagging co-infections or unusual presentations, rather than a Lyme-specific test.

Immune Dysregulation Beyond the Acute Phase

Most of the evidence on white blood cell changes in Lyme disease focuses on the acute phase, before or shortly after treatment begins. What happens to immune cell populations in the weeks and months following treatment is less well characterized. Research into the broader immune dysregulation triggered by Borrelia infection suggests that the effects extend beyond simple cell count shifts. The bacterium’s interaction with the immune system can influence how immune cells function, not just how many are circulating. Altered immune signaling pathways have been linked to the inflammatory manifestations of Lyme disease across several organ systems, including the nervous system, joints, heart, and skin.²

For patients dealing with lingering symptoms after treatment, sometimes labeled post-treatment Lyme disease syndrome, the question of whether ongoing immune changes are driving those symptoms remains an active area of investigation. A persistently abnormal blood count months after adequate antibiotic therapy would be unusual for Lyme disease and should prompt a broader workup for other causes. The acute blood cell shifts documented in research appear to resolve with treatment in most patients, though detailed longitudinal data on post-treatment immune cell dynamics are still limited.

When Low Counts Should Prompt Urgent Attention

A mild dip in lymphocytes during an acute Lyme infection is generally not dangerous on its own and resolves with treatment. There are situations, however, where abnormal blood counts during or after a tick-borne illness warrant urgent medical evaluation:

Severe neutropenia: A neutrophil count below 500 cells per microliter puts you at high risk for secondary infections. This is rare in uncomplicated Lyme disease and should raise suspicion for co-infection or a medication side effect.
Progressive pancytopenia: Simultaneous drops in white cells, red cells, and platelets can indicate babesiosis, a bone marrow disorder, or another serious condition layered on top of Lyme.
High fever with very low counts: A tick-borne fever accompanied by deeply depressed white cells and platelets is more consistent with anaplasmosis or ehrlichiosis than with Lyme disease. These infections require different antibiotic choices and can become dangerous quickly.
Counts worsening on antibiotics: If white cells drop further after starting doxycycline rather than improving, drug-induced neutropenia or an undiagnosed co-infection should be evaluated.

Most people with Lyme disease will never encounter any of these scenarios. The typical course involves a mild immune cell redistribution that resolves as the infection clears. But for the subset of patients whose blood work looks unexpectedly alarming, the distinction between Lyme alone and Lyme with complications or co-infections can be medically significant and time-sensitive.

1
PubMed Central. A sex-based analysis of complete blood count features during acute, untreated Lyme disease
2
PubMed Central. Infection-Triggered Immune Dysregulation and Immunopathology in Lyme Disease: Mechanisms and Clinical Implications
3
The Lancet Regional Health – Europe. Clinical and serological profiles of children with Lyme disease: a 15-year retrospective cohort study in Switzerland
4
SpringerLink / Infection. Pancytopenia in a patient with Lyme disease
5
PubMed Central. Hematologic manifestations of babesiosis
6
Annals of Internal Medicine. Borrelia miyamotoi Disease in the Northeastern United States: A Case Series
7
PubMed Central. Are patients with erythema migrans who have leukopenia and/or thrombocytopenia coinfected with Anaplasma phagocytophilum or tick-borne encephalitis virus?
8
PubMed Central. Recurrent severe neutropenia following doxycycline use in a young healthy woman