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Monocytes

CBC Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: CBC

Overview

Monocytes are a type of white blood cell (leukocyte) produced in the bone marrow that circulate in blood and migrate into tissues to become macrophages and dendritic cells. A monocyte count measures the absolute number or proportion of monocytes among total white blood cells. Abnormal monocyte levels can suggest infections (particularly chronic or certain intracellular infections), inflammatory or autoimmune disorders, recovery from acute infection, bone marrow problems, or hematologic malignancies. Symptoms prompting this test include persistent fever, unexplained fatigue, recurrent infections, enlarged lymph nodes or spleen, and abnormal complete blood count results. Normal values vary with age (young children and infants may have slightly different proportions), physiologic states such as pregnancy, and factors like smoking or recent exercise.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: included in the CBC (complete blood count) with differential.
Symptoms: unexplained fevers, recurrent or chronic infections, fatigue, bruising, lymphadenopathy, abnormal CBC.
Conditions monitored/diagnosed: chronic infections, inflammatory or autoimmune diseases, recovery phase of infection, bone marrow disorders, certain leukemias.
Reasons for abnormal levels: infection, inflammation, marrow suppression or overstimulation, medications (e.g., corticosteroids lower counts), smoking, stress.
Biological meaning: high monocytes (monocytosis) reflect chronic immune activation or marrow proliferation; low monocytes (monocytopenia) indicate impaired marrow production or immune suppression.
Family history: blood cancer or inherited marrow failure syndromes may prompt testing.

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Understanding Test Results

Values below 0.2 x10^9/L (monocytopenia) suggest reduced marrow production or peripheral loss causes include severe acute infections, aplastic anemia, chemotherapy, corticosteroid therapy, or bone marrow infiltration; very low counts increase risk of certain infections.
Values within 0.2–0.8 x10^9/L (2–8%) are considered normal.
Values above 0.8 x10^9/L or >8% indicate monocytosis: mild elevations (0.8–1.0 x10^9/L) often occur during recovery from acute infections or with chronic inflammatory states; persistent or higher elevations (>1.0 x10^9/L) raise concern for chronic infections (e.g., tuberculosis), autoimmune diseases, sarcoidosis, and myeloid disorders such as chronic myelomonocytic leukemia persistent monocytosis merits further evaluation (repeat CBC, differential, infection workup, or bone marrow testing).
Transient rises can also be seen after exercise, smoking, or stress.

Normal Range

0.2-0.8 x10^9/L OR 2-8%

FAQs

Q: What happens if monocyte count is high?

A: A high monocyte count (monocytosis) often signals chronic infection, ongoing inflammation, or immune activation—examples include tuberculosis, viral infections, autoimmune disorders, or recovery from acute infection. It can also reflect blood disorders such as chronic myelomonocytic leukemia. Symptoms depend on the cause; persistent monocytosis calls for repeat blood counts, infection/inflammation evaluation, and possibly bone marrow studies with medical follow-up to identify and treat the underlying issue.

Q: What happens if monocytes are low?

A: Low monocytes (monocytopenia) reduces a key white blood cell that helps fight infections and clear dead cells. Mild decreases may cause no symptoms, but marked or prolonged low counts raise risk of bacterial and fungal infections and suggest bone marrow problems, autoimmune disease, certain medications, or recent chemotherapy. Doctors evaluate with blood tests, review medications and treat the underlying cause; infection precautions may be advised.

Q: Is it better to have higher or lower monocytes?

A: It's better to have monocyte counts within the normal reference range. Elevated monocytes (monocytosis) can signal chronic infection, inflammation, autoimmune disease, or blood cancers; low monocytes (monocytopenia) increases infection risk and may reflect bone marrow suppression or recent chemotherapy. Any abnormal result should be interpreted in context and discussed with your clinician for diagnosis and management.

Q: What is the function of monocytes?

A: Monocytes are circulating white blood cells that form a key part of innate immunity. They patrol the bloodstream, migrate into tissues and differentiate into macrophages and dendritic cells. Their main functions are phagocytosis of pathogens and debris, antigen presentation to T cells, and secretion of cytokines and chemokines to coordinate inflammation, promote pathogen clearance, and support tissue repair and healing.

Q: What cancers cause high monocytes?

A: Cancers commonly linked to persistent monocytosis include chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia with monocytic differentiation. Monocytosis also occurs with myelodysplastic syndromes, other myeloproliferative neoplasms, Hodgkin and non‑Hodgkin lymphomas, and some metastatic solid tumors such as lung, breast, or colorectal cancer. Persistent high monocyte counts warrant hematology evaluation and further testing.

Q: How to treat high monocytes?

A: Treat the underlying cause. Start with repeat CBC, history, exam and tests for infection, autoimmune disease or malignancy. Treatment is cause-specific antibiotics for infections, anti‑inflammatory or immunosuppressive therapy for autoimmune conditions, or hematology referral for suspected blood cancers. Monitor counts and symptoms; lifestyle measures (smoking cessation, control of chronic inflammation) and medical follow‑up for persistent monocytosis.