Complete blood count: number and size of all blood cells

A complete blood count is a set of medical laboratory tests performed on a blood sample to gather information about the number and functionality of blood cells.

The complete blood count encompasses the following tests:

• Red blood cell count
• Hemoglobin levels
• Hematocrit
• Mean corpuscular volume (MCV)
• Mean corpuscular hemoglobin (MCH)
• Mean corpuscular hemoglobin concentration (MCHC)
• Red cell distribution width (RDW)
• White blood cell count
• Neutrophil count
• Monocyte count
• Eosinophil count
• Basophil count
• Lymphocyte count
• Platelet count
• Mean platelet volume (MPV)
• Platelet distribution width (PDW)

Additional, less common tests that may be included are, erythrocyte sedimentation rate, reticulocyte count, blood smears for microscopic examination.

The complete blood count provides a comprehensive view of blood cell health.

Complete blood count results should fall within specific reference ranges. Deviations from these ranges can be concerning.

The complete blood count is used to detect various diseases, such as anemia, infections, and allergies, among others. The specific conditions detected depend on which parameters are abnormal.

The complete blood count test involves the simultaneous analysis of all included parameters.

Elevated red blood cell count, hemoglobin, or hematocrit, may be caused by:

• Dehydration: due to severe diarrhea, excessive sweating, or diuretics used for high blood pressure
• Kidney disease: associated with high erythropoietin production
• Prolonged low oxygen levels: often due to heart or lung disease, carbon monoxide exposure, or living at high altitudes
• Polycythemia vera
• Smoking
• Testosterone use

Low red blood cell count, hemoglobin, or hematocrit, this indicates anemia, which may result from:

• Blood loss (either sudden or due to long-term issues such as heavy menstrual periods)
• Bone marrow failure (e.g., caused by radiation, infection, or a tumor)
• Red blood cell destruction (hemolysis)
• Cancer and its treatments
• Chronic medical conditions, such as chronic kidney disease, ulcerative colitis, or rheumatoid arthritis
• Iron deficiency
• Leukemia
• Prolonged infections like hepatitis
• Poor nutrition and malnutrition, leading to deficiencies in iron, folate, vitamin B12, or vitamin B6
• Multiple myeloma

A white blood cell count below normal is referred to as leukopenia. This reduction may be caused by:

• Alcohol abuse and liver damage
• Autoimmune diseases (e.g., systemic lupus erythematosus)
• Bone marrow failure (e.g., due to infection, tumor, radiation, or fibrosis)
• Chemotherapy medications used to treat cancer
• Liver or spleen disease
• Enlarged spleen (splenomegaly)
• Viral infections, such as mononucleosis or HIV/AIDS
• Medication

A high white blood cell count is called leukocytosis. It can result from:

• Certain medications, such as corticosteroids
• Infections
• Diseases like lupus, rheumatoid arthritis, or allergies
• Leukemia
• Severe physical or emotional stress
• Tissue damage (e.g., from burns or a heart attack)

A high platelet count may result from:

• Bleeding
• Blood disorders or cancer
• Iron deficiency
• Bone marrow problems

A low platelet count may result from:

• Disorders that destroy platelets
• Pregnancy
• Enlarged spleen (splenomegaly)
• Bone marrow failure (e.g., due to radiation, infection, or a tumor)
• Chemotherapy medications used to treat cancer