Red blood cells are the body’s primary transporters of oxygen, delivering it from the lungs to every tissue and organ. Viral illnesses like COVID-19 can trigger effects that extend far beyond the initial site of infection. The widespread nature of the virus has prompted questions regarding its specific impact on these blood components during both acute illness and long-term recovery.
Mechanisms of Red Blood Cell Changes from COVID-19
COVID-19 can alter red blood cell (RBC) counts through two primary, opposing biological pathways. The more common pathway leads to a decrease in red blood cells, a condition known as anemia. Severe COVID-19 is characterized by an intense inflammatory response, or “cytokine storm,” which can suppress the function of bone marrow where new red blood cells are produced. This is categorized as “anemia of inflammation,” where the body has enough iron but cannot use it effectively due to the inflammatory state.
This inflammatory response can also disrupt iron metabolism, limiting the iron available for red blood cell production. In less common scenarios, the immune system can become dysregulated and mistakenly identify red blood cells as foreign invaders. This can lead to autoimmune hemolytic anemia, where the body’s own antibodies attack and destroy red blood cells.
Conversely, COVID-19 can cause an increase in red blood cell count, a state known as secondary polycythemia. This is a compensatory response by the body. When COVID-19 damages the lungs, it can impair the transfer of oxygen into the bloodstream, resulting in low blood oxygen levels, or hypoxia.
The kidneys detect this drop in oxygen and respond by increasing the production of a hormone called erythropoietin (EPO). EPO travels to the bone marrow and stimulates it to ramp up the production of red blood cells to better meet the needs of its tissues.
Recognizing the Symptoms of Abnormal Counts
The symptoms of an abnormal red blood cell count relate to the blood’s capacity to carry oxygen. When the count is too low (anemia), the body’s tissues may not receive enough oxygen to function optimally. This can manifest as persistent fatigue, weakness, and shortness of breath during mild exertion. Other common indicators include pale skin, dizziness, and a rapid heartbeat as the heart works harder to circulate the oxygen-depleted blood.
An elevated red blood cell count (polycythemia) presents symptoms stemming from the increased thickness, or viscosity, of the blood. This thicker blood flows less easily through vessels, which can lead to frequent headaches, blurred vision, and feelings of dizziness or vertigo. Some individuals may develop a reddish complexion on the face, hands, and feet. This condition also brings a heightened risk of blood clots (thrombosis), which can lead to serious events like stroke or pulmonary embolism.
Long-Term Hematological Consequences
For many individuals who recover from an acute COVID-19 infection, red blood cell counts return to their normal range as inflammation subsides and oxygen levels stabilize. However, for some, hematological issues can persist, becoming a feature of post-acute sequelae of COVID-19 (PASC), or Long COVID. Persistent anemia is one of the more frequently reported long-term issues, contributing to the chronic fatigue that characterizes the condition.
The mechanisms driving these long-term changes are still being investigated. Sustained, low-grade inflammation may continue to suppress bone marrow function for months after the initial infection has cleared. Furthermore, research has shown that SARS-CoV-2 can cause structural damage to the red blood cells, affecting their shape and flexibility. These damaged cells are less efficient at navigating the body’s smallest blood vessels and may be cleared from circulation prematurely, contributing to anemia and impairing oxygen delivery.
Diagnostic Testing and Medical Management
Identifying abnormalities in red blood cell counts is done with a blood test called a Complete Blood Count (CBC). This test measures several components of the blood, including the number of red blood cells, the amount of hemoglobin, and the hematocrit. The hematocrit is the proportion of blood composed of red blood cells.
Management of these conditions focuses on addressing the root cause. The primary strategy is to treat the underlying COVID-19 infection and manage its complications, such as controlling the inflammatory response and improving blood oxygen levels. If a specific deficiency contributing to anemia is identified, such as low iron levels, a doctor may prescribe supplements.
In instances of severe anemia, supportive care like blood transfusions may be considered. For polycythemia, medical management is centered on resolving the hypoxia that triggered the overproduction of red blood cells. By improving lung function and oxygenation, the body’s signal to produce excess red blood cells is diminished, allowing the count to normalize over time.