Lyme disease is an infectious illness transmitted through the bite of an infected black-legged tick, primarily caused by the bacterium Borrelia burgdorferi. This tick-borne disease is the most common of its kind in the Northern Hemisphere. The infection often begins with a characteristic expanding rash known as erythema migrans, along with flu-like symptoms such as fatigue and fever. As a systemic infection, Lyme disease can induce various responses throughout the body, including changes in the composition of the blood.
Addressing the Specific Query: Lyme Disease and High Red Blood Cell Counts
A high red blood cell (RBC) count is medically referred to as erythrocytosis or polycythemia, which describes an abnormal increase in the total number of red cells or the concentration of red cells in the blood. When considering the typical course of an infectious illness, Lyme disease is not generally associated with erythrocytosis. Most bacterial or inflammatory diseases tend to trigger the opposite effect, often leading to lower blood cell counts as the body mounts an immune response.
An elevated RBC count is highly unlikely to be a direct consequence of the Borrelia burgdorferi infection itself. Acute symptoms of the illness, such as fever and malaise, can sometimes lead to mild dehydration if fluid intake is insufficient. Dehydration results in a decrease in the liquid portion of the blood, or plasma volume, which effectively concentrates the red blood cells and can cause a temporary, or relative, elevation in the RBC count.
If a patient with Lyme disease exhibits a sustained, true elevation in their red blood cell mass, medical investigation typically focuses on non-infectious causes. This finding is usually treated as a separate, co-occurring medical condition requiring its own specific diagnosis and management plan.
Typical Hematological Manifestations of Lyme Disease
While high red blood cell counts are rare, Lyme disease is known to produce several other hematological changes linked to the body’s inflammatory response to the infection. One common finding is an elevation in general markers of inflammation, such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). These markers are nonspecific, indicating that inflammation is present somewhere in the body without pointing to a particular cause.
A more direct change observed in some patients is a mild reduction in the red blood cell count, a condition known as anemia. Anemia in the setting of an infection is often a consequence of chronic inflammation, where persistent immune activation can suppress the bone marrow’s ability to produce new red cells effectively. This type of anemia is typically mild and resolves once the underlying infection is successfully treated.
Changes in white blood cell and platelet counts are also possible, particularly when a tick transmits multiple pathogens simultaneously, a phenomenon known as co-infection. The same ticks that carry Borrelia can transmit the parasite Babesia microti, which causes babesiosis. Babesiosis specifically targets and destroys red blood cells, leading to a form of anemia called hemolytic anemia, rather than an elevated red cell count.
Other tick-borne co-infections, such as ehrlichiosis or anaplasmosis, can lead to decreased counts of white blood cells (leukopenia) or platelets (thrombocytopenia). If a complete blood count shows multiple abnormalities, it often prompts clinicians to investigate the possibility of these co-infections. In the absence of co-infection, the white blood cell count in Lyme disease can be normal or slightly elevated.
Understanding High Red Blood Cell Counts
When a high red blood cell count, or erythrocytosis, is detected, the underlying cause usually falls into one of two main categories: relative or absolute.
Relative Erythrocytosis
Relative erythrocytosis occurs when the total number of red blood cells remains unchanged, but the plasma volume decreases, causing the blood to appear more concentrated. Severe dehydration, caused by vomiting, diarrhea, or insufficient fluid intake, is the most common reason for this type of transient elevation.
Absolute Erythrocytosis
Absolute erythrocytosis indicates an actual increase in the total mass of red blood cells within the body. This is further divided into primary and secondary causes, each with distinct origins.
Primary erythrocytosis often stems from a problem within the bone marrow itself, such as in the case of Polycythemia Vera (PCV). PCV is a myeloproliferative disorder where a genetic mutation, often in the JAK2 gene, causes the bone marrow to overproduce red cells independently of regulatory signals.
Secondary erythrocytosis is a reactive condition, meaning the body produces more red blood cells in response to an external stimulus, typically low oxygen levels (chronic hypoxia). Conditions like severe lung disease (COPD), chronic heart disease, smoking, or living at high altitudes can reduce the oxygen available to tissues. This lack of oxygen triggers the kidneys to release more erythropoietin, a hormone that stimulates red blood cell production. Rarely, certain kidney tumors or cysts can also cause secondary erythrocytosis by inappropriately producing high levels of erythropoietin.