White blood cells, also known as leukocytes, are a fundamental part of the body’s immune system. Produced in the bone marrow, these specialized cells circulate throughout the bloodstream and lymphatic system. Their primary role involves identifying and combating foreign invaders like bacteria, viruses, fungi, and parasites. They also help remove damaged or dead cells and other debris from the body.
What a Low WBC Count Means
A white blood cell (WBC) count measures the number of these cells in a blood sample, often as part of a routine complete blood count (CBC). For adults, a healthy WBC count typically ranges between 4,000 and 11,000 cells per microliter (µL) of blood, or 4.0-11.0 x 10^9 cells/L. A count of 3.7 (or 3,700 cells/µL) falls below this lower limit, indicating leukopenia. This reduced number suggests a weakened immune system, making the body more vulnerable to infections.
Causes of a Reduced WBC Count
Infections are common causes of a low white blood cell count. Acute viral infections like influenza, HIV, hepatitis, measles, chickenpox, and Epstein-Barr virus often cause a temporary drop. Severe bacterial infections, such as sepsis, can also deplete WBCs as the body rapidly uses them to fight widespread invasion. Certain medications are another cause. Chemotherapy drugs, for instance, target fast-growing cells, including those in the bone marrow that produce white blood cells. Immunosuppressants, some antibiotics (like minocycline), antipsychotics (such as clozapine), interferons, and steroids can also suppress WBC production.
Autoimmune diseases, where the immune system mistakenly attacks healthy body tissues, can also lead to leukopenia. Examples include systemic lupus erythematosus (lupus), rheumatoid arthritis, and Sjögren’s syndrome.
Problems originating in the bone marrow, the site of WBC production, are also frequent causes. These include aplastic anemia (where the marrow fails to produce enough blood cells), myelodysplastic syndromes, and certain cancers like leukemia, lymphoma, or myelofibrosis.
Nutritional deficiencies, especially severe lack of vitamin B12 or folate, can impair white blood cell formation. An enlarged spleen, known as splenic sequestration, can also trap and destroy white blood cells, reducing their numbers in circulation.
Recognizing Symptoms
A low white blood cell count often does not cause direct symptoms. Instead, signs are typically related to the underlying cause or increased susceptibility to infections from a weakened immune defense. Frequent or recurrent infections are common indicators, potentially affecting the respiratory tract, skin, or urinary system.
When an infection occurs, common symptoms include fever and chills, often signaling the body’s struggle against pathogens. Individuals might also experience persistent fatigue or a general feeling of malaise. Other signs can include a sore throat, recurring painful mouth sores, or skin rashes. Coughing, difficulty breathing, and body aches are also possible symptoms, particularly if respiratory infections develop.
What to Do Next
If a blood test reveals a white blood cell count of 3.7, consulting a healthcare professional is the immediate and most important step. This low count requires medical evaluation to determine the underlying cause and appropriate management. The doctor will likely recommend additional diagnostic tests beyond the initial complete blood count. These might include a complete blood count with differential (which details the levels of each specific type of white blood cell), or more specialized tests such as a bone marrow biopsy, specific viral tests, or autoimmune markers.
Treatment for a low WBC count depends on its identified cause. For instance, an infection might be treated with antibiotics, antivirals, or antifungals, while medication adjustments may be necessary if a drug is the culprit. In some cases, particularly with bone marrow issues, medications called colony-stimulating factors (G-CSFs) might be prescribed to stimulate the bone marrow to produce more white blood cells. Regular monitoring of WBC counts will be important to track recovery. Maintaining overall health through a balanced diet, proper hygiene (like frequent handwashing), adequate hydration, and managing stress can support the immune system, though these are supportive measures and not curative for the underlying cause.