References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
HIV attacks the immune system, specifically a type of white blood cell called CD4 T-cells. These cells coordinate your body’s response to infections. Without treatment, HIV gradually reduces CD4 counts until the immune system can’t fight off common infections.
Modern antiretroviral therapy (ART) stops this process, allows CD4 counts to recover, and lets most people live a normal lifespan. Understanding the basics helps you make sense of your test results and treatment.
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What CD4 Cells Do
CD4 T-cells, also called helper T-cells, are the generals of your immune response. They recognise invading viruses and bacteria and signal other immune cells to attack. When HIV infects and destroys CD4 cells, your immune system loses coordination.
Measuring the Immune System: CD4 Count
| CD4 Count (cells/mm³) | What It Means |
|---|---|
| 500 and above | Normal range — healthy immune function |
| 350-499 | Slightly low, monitor closely |
| 200-349 | Weakened, higher infection risk |
| Below 200 | Significant risk of opportunistic infections (AIDS-defining threshold) |
CD4 counts fluctuate naturally and can be affected by illness, stress, and even time of day. Your HIV team looks at the trend over time, not a single result.
Viral Load: How Active the Virus Is
Viral load measures how many copies of HIV are in your blood. The lower the better.
- Detectable — HIV is replicating, usually because treatment hasn’t started or isn’t working
- Undetectable — typically fewer than 20-50 copies per ml (varies by lab). This is the goal of treatment.
Being undetectable means you cannot pass HIV on through sex. This is known as U=U (Undetectable = Untransmittable).
How Treatment Restores the Immune System
Antiretroviral therapy stops HIV from replicating. Once viral load drops, CD4 cells are no longer being destroyed and can start to recover. For most people, CD4 counts rise within months of starting treatment and often return to normal ranges within a year or two, particularly if treatment starts before the count drops very low.
What Helps Your Immune System Stay Strong
- Take ART every day — consistency matters more than anything else
- Attend clinic appointments — your team monitors CD4, viral load and general health
- Stop smoking — smoking accelerates immune ageing
- Eat well and stay active
- Get vaccinated — annual flu, pneumococcal, COVID-19 boosters
- Manage mental health — chronic stress affects immune function
Read more: What is HIV? | Lung problems and HIV | Flu and HIV
Frequently Asked Questions
Can my CD4 count return to normal?
For most people who start treatment before their count drops very low, yes. Recovery is slower if you start with a very low count, but improvement continues for years.
What happens if my CD4 count drops again?
A falling CD4 count usually means HIV is replicating again — often because of missed doses or drug resistance. Your HIV team will investigate and may switch your treatment.
Does being undetectable mean I’m cured?
No. Undetectable means the virus is suppressed to levels too low to be measured or passed on, but HIV is still present in reservoirs in the body. Treatment must continue for life.
Related reading
- Injectable HIV Treatment: Everything You Need to Know
- Are HIV Tests Accurate If You're on PrEP, PEP or ART?
- CD4/CD8 Ratio: What It Means and Why It Matters
- CD4 Counts Explained: What Your Numbers Mean
- Changing HIV Treatment: When, Why and How
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
