Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease where the immune system mistakenly attacks its own tissues and organs. This leads to inflammation and damage, often affecting the skin, joints, kidneys, brain, and blood. Hematological abnormalities are a common feature of SLE. However, a high red blood cell (RBC) count, known as erythrocytosis or polycythemia, is not considered a primary manifestation of Lupus; the disease primarily causes reductions in blood cell counts.
Lupus Typically Causes Low Blood Counts
The standard hematological finding in SLE patients is a reduction in one or more types of blood cells, a condition called cytopenia. This decrease includes low white blood cells (leukopenia), low platelets (thrombocytopenia), and low red blood cells (anemia). Anemia, defined as a low RBC count or low hemoglobin, is common, affecting approximately 50% of people with Lupus.
Chronic inflammation characteristic of Lupus interferes with the body’s normal process of creating and maintaining blood cells. This often leads to Anemia of Chronic Disease (ACD), sometimes called Anemia of Inflammation. In ACD, inflammatory proteins like cytokines disrupt the bone marrow’s ability to produce new red blood cells and hinder the efficient use of iron.
Autoimmune Hemolytic Anemia (AIHA) is another mechanism where the immune system directly destroys existing red blood cells. Autoantibodies bind to the RBC surface, marking them for destruction by scavenger cells or causing premature breakdown in the bloodstream. AIHA is a less frequent cause of anemia in SLE compared to ACD, occurring in about 5% to 10% of patients.
The systemic autoimmune attack also commonly affects other cell lines. Leukopenia, a low white blood cell count, is found in up to 95% of patients and often involves a specific reduction in lymphocytes. Thrombocytopenia, a low platelet count, is also a recognized complication, usually caused by anti-platelet autoantibodies that lead to the destruction of these clotting cells.
Indirect Causes of Elevated Red Blood Cells in Lupus Patients
Despite the typical pattern of low blood counts, a Lupus patient might present with erythrocytosis, which is rarely a direct result of Lupus disease activity. Instead, it is usually a secondary effect of complications or external factors. One such scenario involves severe kidney involvement, a common complication known as Lupus Nephritis.
The kidneys produce erythropoietin (EPO), a hormone that signals the bone marrow to produce red blood cells. While chronic kidney disease from Lupus Nephritis usually causes low EPO and anemia, rare forms of kidney damage or tumors can paradoxically cause EPO overproduction. This excessive stimulation drives the bone marrow to create too many red blood cells, resulting in secondary erythrocytosis.
Medications used to treat Lupus can also indirectly influence the red blood cell count. Corticosteroids, such as prednisone, are a common therapy for managing Lupus flares and inflammation. These drugs can sometimes cause a temporary increase in circulating red blood cells or mask an underlying anemia by influencing plasma volume and bone marrow function.
Dehydration is a common factor leading to an apparently high RBC count. When the body is dehydrated, the liquid portion of the blood, called plasma, decreases in volume. This relative reduction concentrates the remaining blood components, making the red blood cell count appear falsely elevated in laboratory tests. This spurious result can occur in a Lupus patient experiencing a fever or gastrointestinal issues that cause fluid loss.
Other Common Reasons for High Red Blood Cell Counts
When a high red blood cell count is detected, it is often due to causes unrelated to Lupus. Erythrocytosis is broadly categorized into primary and secondary causes, depending on the origin of the increased red blood cell production. Primary erythrocytosis is an intrinsic problem within the bone marrow itself, where the stem cells that produce blood cells malfunction.
Polycythemia Vera (PV), a type of chronic blood cancer known as a myeloproliferative neoplasm, is the most common primary cause. PV is characterized by the overproduction of red blood cells due to a genetic mutation, most frequently in the JAK2 gene. This condition is an independent disease process, separate from the autoimmune mechanisms of SLE, and requires specific diagnosis and management.
Secondary erythrocytosis occurs when an external factor stimulates the bone marrow to produce more red blood cells. The most frequent trigger for this is chronic tissue hypoxia, or a long-term lack of oxygen in the body’s tissues. The body interprets low oxygen levels as a signal to make more oxygen-carrying RBCs.
Conditions that chronically impair oxygen uptake or delivery are common causes of secondary erythrocytosis. These include severe lung diseases like Chronic Obstructive Pulmonary Disease (COPD), obstructive sleep apnea, and certain types of heart disease. Lifestyle factors such as chronic heavy smoking can also induce a state of functional hypoxia, leading to increased RBC production. If a Lupus patient has a high RBC count, the investigation will typically focus on these common non-Lupus related causes first.