Difference Between CBC and CBC with Differential
A CBC with differential provides detailed information about white blood cell types and immature cells, while a standard CBC only reports basic blood cell counts and parameters without this detailed breakdown.
CBC Components
A Complete Blood Count (CBC) is a common laboratory test that includes:
- Red blood cell (RBC) count
- White blood cell (WBC) count (total leukocytes)
- Hemoglobin (Hb) level
- Hematocrit (Hct)
- Red cell indices (MCV, MCH, MCHC)
- Platelet count
- Red cell distribution width (RDW)
CBC with Differential Components
A CBC with differential includes all CBC components plus:
- Breakdown of white blood cell types (differential):
- Neutrophils (%)
- Lymphocytes (%)
- Monocytes (%)
- Eosinophils (%)
- Basophils (%)
- Absolute counts of each WBC type
- Assessment of immature cells (bands/left shift)
- Morphological assessment of cells
Clinical Significance of the Differential
The differential provides critical information for diagnosing and monitoring various conditions:
Bacterial Infections: An elevated total band count (immature neutrophils) has the highest likelihood ratio (14.5) for detecting bacterial infection 1
Left Shift: Increased immature neutrophils (left shift) has a likelihood ratio of 4.7 for bacterial infection 2
Neutrophilia: An increased percentage of neutrophils has a likelihood ratio of 7.5 for bacterial infection 1
Leukocytosis: An elevated WBC count (>14,000 cells/mm³) has a likelihood ratio of 3.7 for bacterial infection 1
When to Order Which Test
Standard CBC (without differential)
- Routine health screenings
- Basic monitoring of known stable conditions
- Initial assessment of anemia
- Monitoring medication effects on blood counts
CBC with Differential
- Suspected infection or inflammation
- Evaluation of fever
- Suspected hematologic disorders
- Monitoring patients with immune disorders
- Evaluation of unexplained symptoms
- Monitoring chemotherapy effects
- Suspected leukemia or other blood cancers
Clinical Applications
The Infectious Diseases Society of America recommends:
A CBC with differential should be performed for all long-term care facility residents suspected of having infection within 12-24 hours of symptom onset 1
For monitoring children with leukemia-predisposing conditions, CBC with differential and reticulocyte count is recommended at varying frequencies depending on the specific condition 1
For suspected Group B streptococcal disease in neonates, a full diagnostic evaluation includes a CBC count with white blood cell differential and platelet counts 1
Laboratory Reporting Considerations
When reporting CBC with differential results:
- Data should be reported in terms of CD designation for specific cell types 1
- Results should be reported as a percentage of total lymphocytes and corrected for lymphocyte purity 1
- Absolute lymphocyte subset values should be calculated when an automated CBC count is performed from blood drawn at the same time 1
Pitfalls and Caveats
Timing matters: Blood samples for CBC with differential should be processed within 24 hours to avoid degradation of cellular components
Interpretation challenges: WBC and differential counts may not reliably distinguish between bacterial and viral infections in all cases due to lack of specificity 3
Reference range variations: Normal values can vary by age, sex, and laboratory
Manual vs. automated differentials: For certain conditions, a manual differential by a trained technologist may be more accurate than automated analysis, particularly for identifying abnormal or immature cells
Cost considerations: CBC with differential is more expensive than standard CBC, so should be ordered when clinically indicated rather than routinely
In summary, while a standard CBC provides basic information about blood cell counts, the differential component offers crucial additional details about white blood cell types and maturity that can significantly impact clinical decision-making, particularly in cases of suspected infection or hematologic disorders.