Lyme disease, caused by the bacterium Borrelia burgdorferi, is the most common vector-borne illness in the United States, transmitted to humans through the bite of an infected black-legged tick. Once transmitted, the spirochete bacteria spread throughout the body, leading to a systemic infection that can affect the skin, joints, heart, and nervous system. This infection provokes an immune response, which can be observed in a person’s complete blood count (CBC), specifically impacting the number of circulating white blood cells (WBCs).
White Blood Cell Count and Lyme Disease
A low total white blood cell count (leukopenia) is not a common finding in early, uncomplicated Lyme disease. The total WBC count is often reported as normal or slightly elevated due to the body’s inflammatory response to the bacterial infection. The lack of a significantly elevated total WBC count is a diagnostic clue when considering Lyme disease over other bacterial infections.
A notable decrease in the total WBC count should raise suspicion for co-infections. The ticks that transmit Borrelia burgdorferi can simultaneously transmit other pathogens, such as those causing anaplasmosis or babesiosis. These co-infections are significantly more likely to cause pronounced leukopenia and thrombocytopenia (low platelet count) than Lyme disease alone. A very low WBC count in a patient with suspected Lyme disease prompts further investigation to rule out these other tick-borne illnesses.
While the total count may be normal, the differential count, which measures the five types of white blood cells, can reveal subtle changes. A reduction in lymphocytes, known as lymphopenia, is sometimes observed in acute Lyme disease. This finding, combined with an otherwise normal total WBC count, can indicate the infection, especially in male patients.
Mechanisms Behind Hematological Changes
The hematological shifts seen during Borrelia burgdorferi infection result from the bacteria’s interaction with the host immune system. The bacteria trigger an inflammatory response involving the release of signaling molecules called cytokines. These cytokines mobilize immune cells and regulate the overall immune process.
This systemic inflammation can temporarily influence the production and distribution of blood cells. Cytokine-driven regulation can lead to a mild, transient suppression of bone marrow activity, resulting in the mild reduction of certain cell lines observed in some patients.
Another mechanism involves the redistribution or sequestration of white blood cells within the body’s reticuloendothelial system, particularly the spleen. Systemic inflammation can cause immune cells to be temporarily held in the spleen, a major site for filtering blood and mounting immune responses. This redistribution leads to a lower number of circulating cells measured in a peripheral blood sample, contributing to mild lymphopenia or other subtle drops in cell counts.
Other Typical Blood Count Abnormalities in Lyme
Other laboratory markers of systemic inflammation are commonly elevated in Lyme disease. The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are frequently increased, reflecting the body’s generalized inflammatory state. These markers confirm the presence of an active inflammatory process.
Mild anemia, specifically normocytic anemia, may also be observed, particularly in later stages or chronic cases. This is often categorized as an “anemia of chronic disease,” where ongoing inflammation interferes with the body’s ability to use iron effectively for red blood cell production. The resulting anemia is typically mild and does not usually require specific treatment beyond addressing the underlying infection.
A decrease in circulating platelets (thrombocytopenia) is occasionally noted in patients with early disseminated Lyme disease. This drop is generally mild and not clinically significant, meaning it rarely leads to bleeding issues. More pronounced thrombocytopenia is a stronger indicator of a co-infection, such as anaplasmosis or ehrlichiosis. Furthermore, the differential WBC count often shows relative lymphocytosis or monocytosis, meaning the proportion of lymphocytes and monocytes is higher than usual as the immune system fights the bacterial invasion.