Complete Blood Count (CBC): A Comprehensive Overview
A Complete Blood Count (CBC) is a fundamental laboratory test that evaluates the cellular components of blood, providing essential diagnostic information for various medical conditions by measuring red blood cells, white blood cells, platelets, and related parameters. 1
Components of a CBC
The CBC consists of several key measurements:
Red Blood Cell Parameters
- Red Blood Cell (RBC) Count: Total number of red blood cells
- Hemoglobin (Hb): Oxygen-carrying protein in red blood cells
- Normal range: 12-16 g/dL for women, 13.5-17.5 g/dL for men 1
- Hematocrit (Hct): Percentage of blood volume occupied by red blood cells
- RBC Indices:
- Mean Corpuscular Volume (MCV): Average size of red blood cells
- Mean Corpuscular Hemoglobin (MCH): Average amount of hemoglobin per red blood cell
- Mean Corpuscular Hemoglobin Concentration (MCHC): Average concentration of hemoglobin in red blood cells
- Red Cell Distribution Width (RDW): Measure of variation in red blood cell size
White Blood Cell Parameters
- White Blood Cell (WBC) Count: Total number of white blood cells
- Normal range: 4,500-11,000/μL 1
- WBC Differential: Percentages of different types of white blood cells
- Neutrophils
- Lymphocytes
- Monocytes
- Eosinophils
- Basophils
Platelet Parameters
- Platelet Count: Total number of platelets
- Mean Platelet Volume (MPV): Average size of platelets
Clinical Significance
The CBC provides valuable information for:
Screening and Diagnosis:
- Anemia (low hemoglobin or hematocrit)
- Infections (elevated white blood cell count)
- Bleeding disorders (low platelet count)
- Hematologic malignancies (abnormal cell counts or morphology)
Disease Monitoring:
- Treatment response in various conditions
- Disease progression
- Medication side effects
Preoperative Assessment:
- Surgical risk evaluation
- Need for blood products 1
Interpretation Considerations
When interpreting CBC results, consider:
- Demographic Factors: Age, sex, pregnancy status, altitude, and ethnicity can affect reference ranges 1
- Multiple Abnormalities: Abnormalities in two or more cell lines (WBC, RBC, platelets) warrant careful evaluation and may require hematology consultation 1
- Clinical Context: Always interpret CBC results in the context of the patient's clinical presentation
Specimen Collection and Handling
- CBC specimens are typically collected in EDTA (lavender-top) tubes
- Most CBC parameters remain stable for up to 72 hours at refrigerated temperatures (4°C) 1
- Proper specimen handling is crucial for accurate results
Advanced Applications
Recent research suggests CBC components can help predict:
- Cardiovascular disease risk
- Metabolic syndrome
- Type 2 diabetes
- Arteriosclerosis 2
Common Pitfalls and Caveats
- Timing of Collection: Recent exercise, stress, or meals can affect results
- Sample Degradation: Delayed processing can lead to inaccurate results
- Normal CBC: Does not rule out certain conditions like early-stage lymphoma 1
- Supplementary Testing: For suspected hematologic malignancies, additional testing beyond CBC is often necessary, including bone marrow examination and specialized testing 1
The CBC is a versatile diagnostic tool that provides crucial information about a patient's health status. Understanding its components and proper interpretation is essential for effective clinical decision-making.