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Easy-to-read and illustrated information on key health monitoring tests for people living with HIV.

It’s important for all people with HIV to have regular blood tests. The two most important blood tests are for CD4 and viral load.

CD4 and viral load test results give essential information about the effect HIV is having on your body.

A CD4 count tells you how many CD4 cells there are in a drop of blood. The more there are, the better. Viral load measures how much HIV there is in a drop of blood.

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CD4 and viral load

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CD4 and viral load
Roger Pebody

Roger Pebody

Commissioning Editor

Roger joined aidsmap in 2008 and was Managing Editor from 2018 to 2024. As a freelancer, he now edits aidsmap’s news and conference coverage, as well as working on updates to About HIV pages. He is also a contributing science editor for TheBodyPro, a freelance journalist for The Lancet HIV, and a medical writer helping researchers prepare articles for peer-reviewed journals. He began working on HIV at Gay Men Fighting AIDS in the mid-1990s.

Basic information

Better off knowing

Better off knowing

What is the difference between HIV and AIDS?

Illustration of HIV virus.

Very recent infection

Very recent infection

Myths and facts

Myths and facts

Undetectable viral load

Undetectable viral load

What is the normal CD4 count for an HIV-negative person?

What is the normal CD4 count for someone taking HIV treatment?

Health checks for people with HIV

Health checks for people with HIV

What does undetectable mean?

Will I test negative if my viral load is undetectable?

What is a viral load blip, and does it matter?

Early HIV infection

A woman site on the sofa with a blanket over her and around her shoulders.

What are the symptoms of early HIV infection?

A woman is resting in bed.

What is the window period for HIV testing?

A person wearing a surgical glove holds the hand of somebody else. This person is having their finger pricked with a fine needle. The needle has drawn a small amount of blood which is visible. The image has a pink and purple filter over it.

CD4 cell counts

A vial of blood is resting on a form that indicates it will be tested for CD4 cells. The image has a pink and purple filter over it.

CD4/CD8 ratio

A person wearing a blue surgical glove holds a vial of blood in front of a bloodwork form. The option "CD4 CD8" is checked. The image has a pink and purple filter over it.

Viral load

A close up of a person's arm while they are having their blood taken. The person taking the blood is wearing surgical gloves. We can see some of the blood is already in the tube.

What are logs in viral load results?

Vial of blood ready for viral load testing