The term “BASOS” on a blood test report is an abbreviation for basophils, a specific type of white blood cell (leukocyte) produced in the bone marrow. Basophils are measured as part of a complete blood count (CBC) with differential, which analyzes the percentages and absolute numbers of white blood cells. While they are the least numerous of all white blood cells, their count provides information about the immune system’s activity, particularly concerning allergies and chronic conditions. An abnormal basophil count, whether high or low, is not a diagnosis but rather a sign that the body is reacting to an underlying process.
Understanding Basophils: Role in the Body
Basophils are classified as granulocytes, a group of white blood cells characterized by granules within their cytoplasm that contain powerful chemical mediators. These cells are fundamentally involved in the body’s immune surveillance and defense, especially against parasites and in allergic responses. Basophils circulate in the blood for a short period before migrating into the tissues where they are needed.
The primary function of basophils centers on the contents of their granules, which include both histamine and heparin. Histamine triggers the symptoms associated with allergic reactions, such as swelling, itching, and increased blood vessel permeability. This promotes blood flow to the affected area as part of the immediate hypersensitivity response.
Heparin, an anticoagulant, is also released by basophils, serving to prevent blood from clotting too quickly at the site of inflammation or injury. This action helps other immune cells and proteins reach the site of a pathogen or foreign substance. Basophils also possess receptors for Immunoglobulin E (IgE), an antibody that binds to allergens, triggering the release of stored chemicals in a process known as degranulation.
Interpreting Normal and Low Counts
Basophils are the rarest type of white blood cell, typically making up only 0.5% to 1% of the total white blood cell count in a healthy adult. The absolute basophil count (ABC), which measures the actual number of cells per volume of blood, is often considered more informative than the relative percentage. A typical normal range for the absolute count is approximately 15 to 50 basophils per cubic millimeter (mm³) of blood.
A result within this narrow range is considered normal, suggesting the basophil population is stable. A low basophil count, known as basopenia, occurs when the absolute number falls below this normal threshold. Basopenia is often less clinically significant than a high count because the cells are naturally so few in number.
Basopenia can occur during acute allergic reactions or anaphylaxis, where the basophils rapidly leave the bloodstream to degranulate in the affected tissues. Low counts may also be associated with certain acute infections or conditions that increase the body’s cortisol levels, such as high stress or the use of corticosteroid medications. An overactive thyroid, or hyperthyroidism, has also been linked to suppressed basophil production in the bone marrow.
Significance of Elevated Basophil Levels
An elevated basophil count, or basophilia, is defined as an absolute count higher than the normal reference range, often exceeding 50 cells/mm³. Because basophils are involved in inflammatory and immune reactions, an increase often signals an ongoing process within the body that requires further investigation. The causes of basophilia can generally be grouped into allergic/inflammatory conditions, endocrine issues, and blood production disorders.
Chronic inflammation and allergic conditions are common causes of a mildly elevated basophil count, as the body ramps up production to deal with a persistent irritant. Conditions such as severe eczema, asthma, food allergies, and inflammatory bowel disease can all lead to an increase in circulating basophils. Certain infections, particularly parasitic ones, also prompt a basophil response due to their role in fighting these pathogens.
Basophilia can also be a sign of endocrine system dysfunction, most notably an underactive thyroid gland, or hypothyroidism. Hypothyroidism is a condition where the thyroid does not produce enough hormones. This condition has been observed to correlate with higher basophil levels, though the exact biological mechanism remains under study.
In more serious instances, a high basophil count can mark myeloproliferative neoplasms, conditions where the bone marrow produces too many blood cells. Diseases like Chronic Myeloid Leukemia (CML) and Polycythemia Vera are frequently associated with basophilia; for CML, an elevated count is a diagnostic criterion. When basophilia is found in isolation, a physician will examine the complete blood picture, including other white and red blood cells, to determine if a bone marrow disorder is possible.