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Why do I need to know my viral load and CD4 count?
If you are not taking anti-HIV drugs, your viral load can provide information on the likely course of HIV infection if left untreated.
A study of viral load levels in untreated people suggests that, in combination with your CD4 count, they may help you to predict your risk of developing symptoms in the future.
Among people with the same CD4 count, research shows that those with higher viral load tend to develop symptoms more quickly than those with lower viral load.
Among people with the same viral load, those with lower CD4 counts tend to develop symptoms more quickly.
As the table on the following page shows, taken together, both CD4 count and viral load provide valuable information to predict the likelihood of developing AIDS in the short to medium term.
If you look at the column for people whose CD4 counts were between 351 and 500, there is a big difference in the risk of disease progression, depending on their viral load.
see table 1 Predicting progression in Viral Load PDF
Researchers have also looked at the risk of developing AIDS or dying for people taking treatment. Monitoring a very large number of people over a number of years they
found that people who did less well on anti-HIV therapy tended to have the following characteristics when they started anti-HIV therapy:
- A CD4 count below 200.
- A viral load above 100,000 copies.
- Age over 50 years.
- Being an injecting drug user.
- Already had an AIDS defining illness.
It is possible to calculate individual disease progression risk by visiting http://www.art-cohort-collaboration.org and entering individual characteristics such as CD4 count, viral load, age, drug use history and past HIV-related illnesses.
Deciding whether to start treatment
The level of your viral load, along with other indicators, may help you to decide whether to start anti-HIV treatment.
At the moment, research evidence which helps doctors make decisions about when people with established (more than six months) HIV infection should start treatment places emphasis on CD4 count rather than viral load. It is recommended that people start treatment before their CD4 count falls below 200, as people who start treatment with a CD4 count below 200 face a greater risk of death, in the short-term, than those who start before their CD4 count drops below this level.
At higher CD4 counts the picture is much less clear, and in these circumstances
timing will depend on the level of viral load, the speed at which CD4 count is falling, the likelihood of achieving good adherence, the presence of symptoms, and the patient’s wishes.
People who are advised to start treatment, but decide not to, should review their decision regularly, and have their CD4 and viral load monitored more regularly.
If you do not receive anti-HIV treatment, the table on page 8 shows that a high viral load, regardless of your CD4 cell count, increases your risk of AIDS-related illness.
Viral load in women
When HIV-positive women and men with the same CD4 cell counts are compared, women tend to have slightly lower viral load on average. However, this doesn't translate into any differences in response to treatment.
CD4 counts and viral load in children
Normal CD4 counts tend to be much higher in very young children than adults. On average the CD4 cell count in a six-month old baby is about 3,000, and is about 1,500 in one year olds and often over 1,000 in infants under six. However, CD4 cell counts stabilise at similar levels to those seen in adults when a child is aged between about six and twelve.
In HIV-positive babies, HIV viral load can rise to very high levels (over 1 million copies/mL) within a few weeks and gradually decline over the first few years of life. The exact reason for this is not known.
The effect of treatment
Effective anti-HIV treatment results in a reduction in viral load. If you start anti-HIV treatment your doctor will test your viral load after four to twelve weeks of treatment to see by how much your viral load has gone down.
Changes in viral load are sometimes expressed using a logarithmic (log) scale.
EXAMPLE
If your viral load falls from 100,000 to 10,000, this is a 1 log reduction.
EXAMPLE
If your viral load falls from 100,000 to 1,000, this is a 2 log reduction.
EXAMPLE
If your viral load falls from 100,000 to 100, this is a 3 log reduction.