From the Guidelines
A Complete Blood Count (CBC) with differential is the preferred test over a CBC without differential in most clinical scenarios, as it provides a comprehensive assessment of blood cells, including a breakdown of white blood cell types, which is crucial for diagnosing and monitoring various conditions, as recommended by the most recent study 1. When evaluating for infections, inflammatory conditions, leukemias, allergic reactions, immune disorders, or monitoring response to medications that affect white blood cells, a CBC with differential is the more informative choice. The differential adds valuable diagnostic information by revealing patterns in white blood cell populations that can point to specific disease processes. For example, elevated neutrophils often indicate bacterial infections, while increased lymphocytes may suggest viral infections. Some key points to consider when ordering a CBC with or without differential include:
- The presence of an elevated WBC count or a left shift warrants a careful assessment for bacterial infection, as noted in 1 and 1.
- In the absence of fever, leukocytosis, and/or left shift, or specific clinical manifestations of a focal infection, additional diagnostic tests may not be indicated, as stated in 1 and 1.
- A CBC with differential is recommended for surveillance in children with predisposition to hematopoietic malignancy, as outlined in 1 and 1.
- The frequency of CBC evaluations may vary depending on the specific condition and risk of hematologic malignancy, as detailed in 1. Overall, the CBC with differential is a valuable diagnostic tool that provides essential information for diagnosing and managing a wide range of conditions, and its use is supported by the most recent and highest quality evidence 1.
From the Research
Rationale for Ordering a Complete Blood Count (CBC) with or without Differential (Diff)
The rationale for ordering a CBC with or without differential is based on the clinical need to assess various blood cell parameters. The following points highlight the key considerations:
- A CBC with differential provides information about the production of all blood cells, including red blood cell (RBC) indices, hemoglobin, and hematocrit, as well as the immune system through the evaluation of the white blood cell (WBC) count with differential 2.
- This test is helpful in diagnosing anemia, certain cancers, infection, acute hemorrhagic states, allergies, and immunodeficiencies, as well as monitoring for side effects of certain drugs that cause blood dyscrasias 2.
- The differential component of the test may not always be necessary, and its overutilization can lead to increased costs and turnaround times 3, 4.
- Studies have shown that interventions such as educational programs and changes to electronic medical record (EMR) ordering systems can reduce the overutilization of CBC with differential testing without negatively impacting patient care 3, 4.
- The use of point-of-care CBC analyzers can also facilitate rapid quantitative assessment of CBC parameters, particularly in outreach clinic settings and for critically ill patients 5.
- Clinical decision support alerts can be effective in reducing unnecessary orders for CBC with differential, resulting in decreased test volumes and improved turnaround times 6.