Background

The Complete Blood Count (CBC) test is one of the most routinely used laboratory tests in clinical medicine which provide valuable information about a patient’s general health. It contains extensive information about the biological components of blood like red blood cells (RBCs), white blood cells (WBCs) and platelets. This test is an important diagnostic tool for detecting, diagnosing and monitoring a wide range of medical disorders like infections, anemia, hematologic malignancies and systemic diseases.

Components of the CBC

A CBC test consists of different parameters and each of which provides specific details about different blood components:

Red Blood Cell Indices

• Red Blood Cell Count (RBC): It determines the number of RBCs per microliter of blood. Abnormal results can suggest disorders like anemia (low RBC count) or polycythemia (high RBC count).
• Hemoglobin (Hb): It measures the capacity of blood to transport oxygen. Reduced Hb levels indicate anemia but increased levels can occur with polycythemia or chronic hypoxia.
• Hematocrit (Hct): The % of blood volume filled by RBCs. It connects with RBC and Hb levels.
• Mean corpuscular volume (MCV): It refers to the average size of RBCs. It helps in the classification of anemia into microcytic, normocytic and macrocytic.
• Mean corpuscular hemoglobin (MCH): It represents the average quantity of Hb/RBC.
• Mean Corpuscular Hemoglobin Concentration (MCHC): It is the average Hb concentration in a given volume of RBCs.
• Red Cell Distribution Width (RDW): It determines the variance in RBC size which helps in the identification of mixed anemia types.

White Blood Cell Indices

• White Blood Cell Count (WBC): It is an important measure of immune system function. A high levels of WBC indicate infections, inflammation or leukemia. A lower counts indicate bone marrow suppression or specific infections.

Differential WBC count categorizes the 5 categories of WBCs:

• Neutrophils: It play an important role in bacterial infection defense.
• Lymphocytes: They are essential to adaptive immunity especially in viral infections and chronic immunological disorders.
• Monocytes: They are phagocytic and antigen-presenting cells.
• Eosinophils: They are linked with allergic responses and parasite diseases.
• Basophils: They are involved in hypersensitivity and inflammation responses.

Platelet Indices

• Platelet Count: This reflects the number of platelets that are required for clot formation. Abnormal counts might suggest thrombocytopenia (low count) or thrombocytosis (high count).
• Mean Platelet Volume (MPV): It measures the average size of platelets and provides information on platelet production and activity.
• Platelet Distribution Width (PDW): It measures platelet size variability.

Indications/Applications

Diagnostic Applications of CBC: It identifies anemia caused by dietary deficits, chronic disease or bone marrow problems. It detects polycythemia caused by increased RBCs or prolonged hypoxia. IT also diagnoses leukemia and lymphoma based on aberrant WBC counts or morphology. It emphasizes thrombocytopenia or thrombocytosis caused by bleeding or clotting issues.

Monitoring Applications: It tracks the effects of chemotherapy or radiation on bone marrow, chronic diseases like renal failure, autoimmune disorders and persistent infections. It assesses immunological response using WBC counts.

Screening Applications: It detects asymptomatic diseases like mild anemia and chronic inflammation, early nutritional deficits, anemia, thrombocytopenia and infections that might compromise surgery.

Pediatric and neonatal Applications: It screens for congenital abnormalities and infections.

Occupational health: It monitors radiation and harmful chemical exposure.

Reference Range

The normal range of CBC test:

RBC count:

Women: 4.2 – 5.4 million cells/mcL

Men: 4.6 – 6.2 million cells/mcL

WBC Indices:

WBC count: 4,500 – 10,000 cells/mcL

Lymphocytes:1000 to 4000/mm³ or 20 to 40%

Neutrophils: 2500 to 8000/mm³ or 55 to 70%

Eosinophils: 50 to 500/mm³ or 1 to 4%

Monocytes: 100 to 700/mm³ or 2 to 8%

Basophils: 25 to100/mm³ or 0.5 to 1%

Hematocrit:

Women: 36.1 – 44.3%

Men: 40.7 – 50.3%

Hb:

Women: 12.0 – 16.0 gm/dL

Men: 14.0 – 18.0 gm/dL

Pregnant female: Below 11 gm/dL

RBC indices:

MCH: 27 – 31 pg/cell

MCV: 80 – 95 femtoliter

MCHC: 32 – 36 gm/dL

Platelet count:

150,000/dL – 450,000/dL

Normal range can vary a little among laboratories. Some laboratories take various measures or test various specimen.

Interpretation

Elevate RBC, Hb or hematocrit can be because of:

A lack of fluids and water like excessive sweating, severe diarrhea or water pills which are used to treat the high blood pressure

Kidney disease with elevated production of erythropoietin

Decrease level of oxygen in blood for long time because of lung or heart disease, exposure to chronic carbon monoxide or staying at high altitude

Smoking

Polycythemia vera

Usage of testosterone

Reduces RBC, Hb or hematocrit indicate anemia which may be caused by:

Loss of blood because of heavy menstrual cycle for prolonged time

Hemolysis

Bone marrow failure because of infection, radiation or tumor

Cancer

Deficiency of iron

Cancer treatment

Leukemia

Prolonged infection like hepatitis

Multiple myeloma

A reduced count of WBC is known as leukopenia. It is because of:

Liver damage

Alcohol abuse

Autoimmune diseases like Systemic lupus erythematosus (SLE)

Chemotherapy drugs to treat cancer

Bone marrow failure because of radiation, tumor, infection, fibrosis

Spleen or liver disease

Enlarged spleen

Medicine

Infections which are caused by virus like AIDS or mono

An elevated WBC count is known as leukocytosis. It is caused by:

Infections

Medicines like corticosteroids

Diseases like rheumatoid arthritis, allergy or lupus

Severe physical or emotional stress

Tissue damage like heart attack or burns

An elevated platelet count is because of:

Diseases like blood disease or cancer

Deficiency of iron

Bleeding

Bone marrow problems

A reduced platelet count is because of:

Disease which can destroy platelets

Enlarged spleen

Pregnancy

Chemotherapy drugs to treat cancer

Bone marrow failure because of tumor, infection, radiation, fibrosis

Collection And Panels

Sample type: Whole blood

Sample collection method: Venipuncture

Sample collection tube: EDTA tube, lavender tube which contains EDTA potassium salt as an anticoagulant

Sample volume: 2 mL

Sample minimum volume: 0.5 to 1 mL

Sample storage: Store sample for 4 to 6 hours a room temperature or 2 to 8 °C for 24 hours in refrigerator.

References

https://www.ncbi.nlm.nih.gov/books/NBK604207/