PMNs, also known as neutrophils, are a type of white blood cell and the most abundant granulocyte in the bloodstream. They are a primary component of the body’s innate immune system, acting as immediate responders. Their main function involves rapidly migrating to sites of infection or inflammation to combat invading microorganisms and clear cellular debris. An abnormal PMN count, detected through a blood test, indicates that the number of these immune cells is outside the typical range.
Understanding PMN Count Results
An abnormal PMN count can be either elevated or reduced. A high PMN count is termed neutrophilia, indicating an increased number of neutrophils. Conversely, a low PMN count is known as neutropenia, signifying a decreased level of these cells.
These counts are determined through a Complete Blood Count (CBC) with differential. This test quantifies blood components, including white blood cells, and breaks down the percentages of each type. Laboratory reports display a “reference range” for PMN counts. Any result outside this range is flagged as abnormal, prompting further investigation.
Causes of a High PMN Count
An elevated PMN count, or neutrophilia, most frequently arises from the body’s response to an ongoing infection. Bacterial infections, such as pneumonia or urinary tract infections, are common triggers. The immune system floods the bloodstream with neutrophils to fight pathogens, and the bone marrow increases production, leading to higher numbers in circulation.
Non-infectious inflammatory conditions also commonly increase PMN levels. Diseases like rheumatoid arthritis or gout can stimulate neutrophil production. Tissue damage from events such as severe burns, major surgery, or heart attacks similarly prompts an inflammatory response that elevates PMN counts.
Certain physiological stresses can temporarily raise PMN levels. Intense physical exertion or emotional stress can induce a transient increase in circulating neutrophils. Pregnancy is another physiological state that can naturally lead to a mild elevation in PMN counts, particularly during later trimesters.
Some medications cause neutrophilia as a side effect. Corticosteroids, prescribed for inflammatory conditions, are a frequent culprit, mobilizing neutrophils from the bone marrow into the bloodstream. Lithium, used to treat bipolar disorder, can also stimulate the production of white blood cells, including PMNs.
In less common but serious instances, malignancies, particularly certain blood cancers, can lead to persistently high PMN counts. Chronic myeloid leukemia (CML), for example, is characterized by an overproduction of granulocytes, including neutrophils, in the bone marrow. This uncontrolled proliferation results in a sustained elevation of PMNs in the blood.
Causes of a Low PMN Count
A reduced PMN count, known as neutropenia, can stem from issues affecting the production or survival of these cells. Conditions that impair the bone marrow, the body’s primary site for blood cell production, are significant causes. Aplastic anemia, where the bone marrow stops producing enough new blood cells, directly leads to neutropenia. Similarly, chemotherapy and radiation therapy can severely damage bone marrow cells, reducing PMN production.
While bacterial infections often increase PMN counts, some severe bacterial infections, like sepsis, can rapidly deplete neutrophils as they are consumed at the infection site. Certain viral infections also suppress bone marrow activity or directly affect neutrophil survival. Viruses like influenza, hepatitis, and HIV can decrease PMN levels by impairing their production or accelerating their destruction.
Autoimmune disorders are another cause of neutropenia. In conditions like systemic lupus erythematosus (lupus) or rheumatoid arthritis, the body’s immune system mistakenly attacks and destroys healthy cells, including circulating PMNs. This leads to a reduction in the neutrophil count.
Medications are a common cause of drug-induced neutropenia. A range of drugs can have this side effect, including certain antibiotics, some antipsychotics, and many chemotherapy agents. These medications can suppress bone marrow activity or cause premature destruction of neutrophils.
Nutritional deficiencies can also impair the body’s ability to produce sufficient PMNs. Deficiencies in specific vitamins, particularly B12 and folate, disrupt the normal maturation and division of blood cells in the bone marrow. This impairment can lead to ineffective neutrophil production, resulting in lower circulating counts.
Diagnosis and Next Steps
An abnormal PMN count is a finding, not a definitive diagnosis. It indicates that further investigation is warranted to uncover the underlying cause. Healthcare professionals begin by reviewing the patient’s medical history, including recent illnesses, medications, and any chronic conditions.
A comprehensive physical examination is also a standard part of the diagnostic process. It can reveal signs or symptoms related to potential causes, such as swollen lymph nodes, signs of infection, or joint inflammation. Based on these initial assessments, the doctor may order additional tests to pinpoint the reason for the abnormal count. This could involve repeating the blood test to see if the count normalizes or persists.
Further laboratory tests might include checking inflammatory markers, such as C-reactive protein (CRP), which can indicate inflammation or infection. If bone marrow issues are suspected, a bone marrow biopsy may be necessary. This involves taking a small sample of bone marrow for microscopic examination. Ultimately, treatment for an abnormal PMN count addresses the underlying condition, rather than merely treating the count itself. Consulting a healthcare professional is important for accurate interpretation and guidance.