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CD4 Counts
What is the CD4 count?
CD4 cells, or T-helper cells, are white blood cells which organise the immune system's response to some microorganisms, including bacteria, fungal infections and viruses.
The CD4 count is the measurement of the number of CD4 cells, in a cubic millimeter of blood (not the whole of your body). This is sometimes written as CD4 cells/mm3.
The CD4 count of a person who is not infected with HIV may lie anywhere between 500 and 1200. HIV can infect CD4 cells and use them to produce more HIV copies.
Even while a person with a HIV feels well and has no symptoms, millions of CD4 cells are infected by HIV and are destroyed each day, and millions more CD4 cells are produced to replace them.
What CD4 counts predict
Most people with HIV find that their
CD4 count usually declines over a number of years.
A CD4 count between 500 and 200 indicates that some damage to the
immune system has occurred. If your CD4 count drops below 350, or starts falling rapidly, your doctor should talk with
you about whether you need to start anti-HIV treatment.
If your CD4 count falls below 250-200 you are recommended to start treatment with anti-HIV drugs because this is the level at which the risk of AIDS-related illness is greatly increased.
The most important information that your CD4 count can give you is the overall trend of your immune system's health – whether it is declining or improving.
Changes in the CD4 count
Your CD4 count can go up and down in response to infections, stress, smoking, exercise, the menstrual cycle, the contraceptive pill, the time of day and even the seasons of the year. Different types of CD4 counting-machine also give different readings.
This is why it is important to monitor its trend over time, rather than to focus too much on individual test results. It's also best to have your CD4 count measured at the same clinic and at roughly the same time of day wherever possible. If you have an infection like flu or herpes it is best to delay having a CD4 count until you are feeling better.
If you have a relatively high CD4 count, no symptoms and you are not taking anti-HIV drugs, you only need to measure your CD4 count once every three months.
However, if your count has been falling rapidly, or you are taking part in a clinical trial, or you have just started new treatment, your doctor may suggest that your count should be monitored more often.
If you are experiencing very wide variations in your CD4 count then it could be because your overall white blood cell count has changed, possibly in response to an infection. In these circumstances your doctor may look at other test results which give an indication of the state of the immune system, such as the CD4/CD8 ratio, or CD4 percentage to decide if the wide variation in CD4 count is important.
CD4 percentages
Instead of counting the number of CD4 cells per mm3, doctors sometimes assess what proportion of all white blood cells are CD4 cells. This is called the CD4 cell percentage; in HIV-negative people, a normal result is about 40%. A CD4 percentage below about 20% is thought to reflect the same risk of becoming ill because of HIV as a CD4 count of about 200.
CD4 cells, or T-helper cells, are white blood cells which organise the immune system's response to some microorganisms, including bacteria, fungal infections and viruses.
The CD4 count is the measurement of the number of CD4 cells, in a cubic millimeter of blood (not the whole of your body). This is sometimes written as CD4 cells/mm3.
The CD4 count of a person who is not infected with HIV may lie anywhere between 500 and 1200. HIV can infect CD4 cells and use them to produce more HIV copies.
Even while a person with a HIV feels well and has no symptoms, millions of CD4 cells are infected by HIV and are destroyed each day, and millions more CD4 cells are produced to replace them.
What CD4 counts predict
Most people with HIV find that their
CD4 count usually declines over a number of years.
A CD4 count between 500 and 200 indicates that some damage to the
immune system has occurred. If your CD4 count drops below 350, or starts falling rapidly, your doctor should talk with
you about whether you need to start anti-HIV treatment.
If your CD4 count falls below 250-200 you are recommended to start treatment with anti-HIV drugs because this is the level at which the risk of AIDS-related illness is greatly increased.
The most important information that your CD4 count can give you is the overall trend of your immune system's health – whether it is declining or improving.
Changes in the CD4 count
Your CD4 count can go up and down in response to infections, stress, smoking, exercise, the menstrual cycle, the contraceptive pill, the time of day and even the seasons of the year. Different types of CD4 counting-machine also give different readings.
This is why it is important to monitor its trend over time, rather than to focus too much on individual test results. It's also best to have your CD4 count measured at the same clinic and at roughly the same time of day wherever possible. If you have an infection like flu or herpes it is best to delay having a CD4 count until you are feeling better.
If you have a relatively high CD4 count, no symptoms and you are not taking anti-HIV drugs, you only need to measure your CD4 count once every three months.
However, if your count has been falling rapidly, or you are taking part in a clinical trial, or you have just started new treatment, your doctor may suggest that your count should be monitored more often.
If you are experiencing very wide variations in your CD4 count then it could be because your overall white blood cell count has changed, possibly in response to an infection. In these circumstances your doctor may look at other test results which give an indication of the state of the immune system, such as the CD4/CD8 ratio, or CD4 percentage to decide if the wide variation in CD4 count is important.
CD4 percentages
Instead of counting the number of CD4 cells per mm3, doctors sometimes assess what proportion of all white blood cells are CD4 cells. This is called the CD4 cell percentage; in HIV-negative people, a normal result is about 40%. A CD4 percentage below about 20% is thought to reflect the same risk of becoming ill because of HIV as a CD4 count of about 200.