CD4+ T Cell Count
CD4· also: CD4 Count, T-cell count, CD4+ T lymphocytes
Clinical Overview
CD4+ T cells (helper T cells) are the primary target of HIV. The CD4 count measures the number of CD4+ T lymphocytes per microliter of blood and reflects the current state of immune function in HIV-positive patients. It is the most important monitoring tool for HIV disease progression and is used to guide antiretroviral therapy initiation and opportunistic infection prophylaxis.
Why This Test Matters
CD4 count is the primary marker of immune status in HIV. A count below 200 cells/µL defines AIDS and is the threshold for starting prophylaxis against Pneumocystis jiroveci pneumonia (PCP), the most common AIDS-defining opportunistic infection. CD4 <100 requires toxoplasmosis prophylaxis; CD4 <50 requires MAC (Mycobacterium avium complex) prophylaxis. Antiretroviral therapy (ART) is recommended for all HIV-positive patients regardless of CD4 count, but urgency increases as CD4 falls. With effective ART, CD4 count typically rises by 100–200 cells/µL per year. Goals of ART include viral suppression AND CD4 restoration above 500 cells/µL. CD4:CD8 ratio (normal >1.0) is a measure of immune activation; a persistently low ratio despite viral suppression indicates ongoing immune dysregulation.
Reference RangesWHO/IFCC standards
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 500 – 1500 | cells/µL | Normal immune function |
| All ages | 200 – 499 | cells/µL | Moderate immunosuppression |
Also reported in: cells/mm³.
Critical (Panic) Values
Critical Low: < 200 cells/µL. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High CD4 Causes
- Effective antiretroviral therapy (ART) restoring immune function
- In HIV-negative individuals: normal immunological variation, infections (reactive lymphocytosis)
Low CD4 Causes
- HIV infection (progressive CD4 depletion)
- AIDS (CD4 <200 cells/µL)
- Corticosteroid therapy (reduces CD4 counts transiently)
- Acute illness or surgery (transient decrease)
- Diurnal variation (CD4 is lower in the morning)
Signs & Symptoms to Watch For
How to Prepare for This Test
CD4 count has significant biological variation: time of day (higher in evening), intercurrent illness, and technical factors affect results. Ideally measure consistently at the same time of day. Recent infection or vaccination can transiently lower CD4 count — avoid measuring during acute illness. A single CD4 count below a threshold should be confirmed with a repeat before making major clinical decisions.
Factors That Can Affect Results
- Diurnal variation (counts are ~25% higher in afternoon vs. morning)
- Acute illness, infections, and vaccinations temporarily reduce CD4 count
- Corticosteroids reduce CD4 counts
- Sample processing delays (>24 hours may affect accuracy)
- Splenectomy can cause CD4 redistribution
Related Topics
Frequently Asked Questions
My CD4 count is 180 — do I have AIDS? What should I do?
A CD4 count below 200 cells/µL meets the definition of AIDS, which means your immune system is severely compromised. This is a serious finding that requires immediate action. You should: start or optimize antiretroviral therapy (ART) immediately if not already on it, start PCP prophylaxis (usually cotrimoxazole/trimethoprim-sulfamethoxazole), and see an infectious disease specialist urgently. With effective ART, CD4 counts typically recover significantly over 1–2 years, and most AIDS-defining conditions become preventable.
My HIV viral load is undetectable but my CD4 count is still low — is this normal?
This is a recognized phenomenon called immunological non-response or immune non-reconstitution. About 15–20% of HIV patients achieve viral suppression with ART but have delayed or incomplete CD4 recovery. Risk factors include starting ART with a very low baseline CD4 count, older age, and coinfections (CMV, HCV). A persistently low CD4 count despite viral suppression means you remain at risk for opportunistic infections and may need to continue prophylactic antibiotics. Your doctor may consider testing for coinfections and adjunctive therapies.