Red blood cells (erythrocytes) transport oxygen, while white blood cells (leukocytes) defend the body against infection. A complete blood count (CBC) measures these cells. Low counts can indicate an underlying health issue, requiring investigation for proper diagnosis and management.
Reasons for Low Red Blood Cells
A low red blood cell count, known as anemia, can stem from various causes. Nutritional deficiencies are a common factor. Iron is essential for producing hemoglobin, the protein within red blood cells that binds oxygen. Deficiencies in vitamin B12 and folate also lead to anemia, as these vitamins are necessary for proper red blood cell development in the bone marrow.
Blood loss, whether acute (injury, surgery) or chronic (gastrointestinal bleeding, heavy menstrual periods), significantly reduces red blood cell counts. The body loses red blood cells faster than it can produce new ones.
Problems within the bone marrow, where blood cells are produced, can also cause low red blood cell counts. Aplastic anemia, for example, involves the bone marrow failing to produce enough new blood cells. Myelodysplastic syndromes are another group of conditions where the bone marrow produces defective red blood cells that do not function correctly or die prematurely.
Chronic diseases frequently contribute to anemia. Kidney disease can lead to reduced production of erythropoietin, a hormone that stimulates red blood cell formation in the bone marrow. Anemia of chronic disease, often associated with long-term infections, inflammatory conditions, or cancer, results from inflammation that traps iron and suppresses red blood cell production.
Conditions that cause premature destruction of red blood cells, known as hemolysis, can also result in anemia. Autoimmune hemolytic anemia occurs when the immune system mistakenly attacks and destroys the body’s own red blood cells. Certain infections or medications can also trigger this accelerated breakdown of red blood cells.
Reasons for Low White Blood Cells
A reduced white blood cell count, medically termed leukopenia, often compromises the body’s immune defenses. Infections are a frequent cause. Viral infections like influenza, HIV, measles, Epstein-Barr virus, and parvovirus B19 can temporarily suppress bone marrow activity or directly affect white blood cell production. Severe bacterial infections, such as sepsis, can also lead to leukopenia as the immune system becomes overwhelmed and white blood cells are consumed rapidly.
Autoimmune diseases can target and destroy white blood cells. Systemic lupus erythematosus commonly causes leukopenia, particularly a decrease in lymphocytes and sometimes neutrophils. Rheumatoid arthritis is another autoimmune condition that can lead to lower white blood cell counts.
Disorders originating in the bone marrow, the site of white blood cell production, are also significant causes. Aplastic anemia impairs the bone marrow’s ability to produce blood cells, affecting white blood cells alongside red blood cells. Myelodysplastic syndromes can result in the production of abnormal, non-functional white blood cells or a reduced number of healthy ones. Certain leukemias can initially present with low white blood cell counts.
Various medications are known to suppress white blood cell production. Chemotherapy drugs, designed to kill rapidly dividing cells, often reduce white blood cell counts as a side effect. Immunosuppressants, specific antibiotics, and antipsychotic medications are additional examples of drugs that may lead to a decrease in white blood cells.
Severe nutritional deficiencies, particularly a lack of vitamin B12 or folate, can sometimes impact the bone marrow’s ability to produce white blood cells. An overactive spleen, known as hypersplenism, can trap and destroy white blood cells, leading to lower counts in the bloodstream.
Causes Affecting Both Cell Types
Some conditions can simultaneously reduce both red and white blood cell counts, a state referred to as pancytopenia. Bone marrow failure is a primary reason for this combined reduction. Aplastic anemia exemplifies this, as it involves the bone marrow’s inability to produce sufficient quantities of all types of blood cells. Certain cancers, including leukemias, lymphomas, and multiple myeloma, can infiltrate the bone marrow, displacing healthy blood-forming cells and leading to a decrease in multiple cell lines. Metastatic cancers that spread to the bone marrow can also cause this effect.
Severe, overwhelming infections, such as sepsis, can suppress overall bone marrow function, leading to a drop in both red and white blood cell counts. Viral infections like HIV can also impair the bone marrow’s ability to produce blood cells.
Certain medications and treatments are designed to affect rapidly dividing cells, which includes blood-forming cells in the bone marrow. Chemotherapy and radiation therapy, commonly used in cancer treatment, are well-known for their broad suppressive effects on bone marrow, leading to reduced production of both red and white blood cells. Other drugs, including some anticonvulsants, can also have this effect.
Systemic autoimmune diseases, such as systemic lupus erythematosus, can occasionally affect multiple blood cell lines, contributing to pancytopenia. Severe liver disease, particularly cirrhosis, can lead to an enlarged and overactive spleen (hypersplenism), which then traps and removes various blood cells from circulation. Exposure to certain industrial chemicals or heavy metals, like arsenic or benzene, can also damage bone marrow and result in reduced blood cell production.
How Doctors Identify the Causes
Identifying the underlying cause of low red and white blood cell counts involves a systematic approach. Doctors typically begin by taking a detailed patient history, inquiring about symptoms, medical conditions, medications, and lifestyle factors. A physical examination helps assess overall health and look for signs related to blood count abnormalities.
A complete blood count (CBC) with differential is usually the initial diagnostic test. This blood test provides precise measurements of red blood cells, white blood cells, and platelets, and also categorizes the different types of white blood cells, which can offer clues about the specific cause.
If the CBC results are abnormal, further blood tests are often ordered. These may include tests for iron levels, vitamin B12, and folate to check for nutritional deficiencies. Kidney and liver function tests are conducted to assess organ health, and inflammatory markers or autoimmune markers might be checked if an inflammatory or autoimmune condition is suspected.
In cases where bone marrow issues are suspected or the cause remains unclear, a bone marrow biopsy and aspiration may be performed. This procedure involves collecting a small sample of bone marrow for microscopic examination, allowing doctors to evaluate the production of blood cells and identify any abnormalities. Imaging studies, such as ultrasound or CT scans, might be used to check for organ enlargement or tumors that could be affecting blood cell production or destruction.