From the Guidelines
Flow cytometry results for CD4 T-cells should be interpreted by examining both the absolute CD4 count (cells/μL) and the CD4 percentage of total lymphocytes, with the CD4 percentage being somewhat less variable than the absolute count. When interpreting CD4 cell counts, it is essential to consider the substantial variation that can occur, especially during acute illness, and the potential effects of various medications and intercurrent illnesses 1. The absolute CD4 cell count is the number most often used in clinical practice, but the CD4 cell percentage can also be used to assess immune function.
Key Considerations
- Total CD4 cell counts of 200 and 500 cells/µL generally correspond to CD4 cell percentages of 14% and 29%, respectively, as noted in the guidelines for the management of persons infected with HIV 1.
- In children aged <5 years, there is more variability in the absolute CD4 count, making CD4 percentage generally preferred for monitoring immune status.
- The CD4/CD8 ratio is not necessary for clinical decision making, as stated in the guidelines, which recommend against measuring the CD8 cell count and the ratio of CD4 cells to CD8 cells 1.
Clinical Application
- A CD4 cell count with percentage should be obtained upon initiation of care, as recommended by the HIV Medicine Association of the Infectious Diseases Society of America 1.
- Providers and patients should be aware of the potential fluctuations in CD4 cell counts and interpret results with caution, especially during acute illness or when the patient is taking certain medications.
- Laboratory variability can cause fluctuations, so it is crucial to confirm significant changes with repeat testing and consider the patient's baseline values, recent trends, concurrent viral load, and clinical status when interpreting results.
From the Research
Interpreting Flow Cytometry Results for CD4
Overview of CD4 Cell Count
- CD4 cell count is a critical marker for assessing the immune system's health, particularly in individuals with HIV/AIDS 2, 3.
- A lower CD4 cell count is associated with a higher risk of opportunistic diseases and death 3.
- The CD4 cell count can be used to guide antiretroviral therapy (ART) and monitor treatment response 2, 4.
Factors Affecting CD4 Cell Count
- Baseline CD4 cell count is a significant predictor of treatment outcomes, with lower counts associated with poorer outcomes 2, 3.
- CD4 cell count recovery is also an important factor, with suboptimal recovery associated with an increased risk of virological failure 2.
- Other factors, such as age, viral load, and ART regimen, can also impact CD4 cell count 4, 5.
Clinical Implications
- CD4 cell count-guided interruption of ART is not recommended, as it can lead to an increased risk of opportunistic diseases and death 3.
- ART regimens that include efavirenz, tenofovir, and emtricitabine have been shown to be effective in increasing CD4 cell count and suppressing viral load 2, 6.
- Regular monitoring of CD4 cell count and viral load is essential for optimizing treatment outcomes and preventing treatment failure 2, 4.