If you are not currently taking anti-HIV treatment

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 (assuming there is no treatment).

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.

(table)

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 less clear, current guidelines suggest that 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.

However, evidence is mounting that starting treatment earlier, at CD4 cell counts of around 350 cells/mm³, may have benefits.

Serious non-AIDS defining illnesses (like heart disease, serious kidney disease, liver cirrhosis and some non-AIDS defining cancers) occur more frequently than AIDS-defining illnesses in patients with higher CD4 cell counts. Studies have shown that earlier treatment may help to reduce the risk of some of these occurring.

Other evidence shows that the CD4 cell rise seen with anti-HIV therapy is predicted by the level of damage already caused, before treatment has started, and by the nadir (lowest ever) CD4 cell count reached during chronic infection. There is also evidence from the UK that people with a CD4 count between 200 and 250 when taking treatment are around five times more likely to develop an AIDS-related illness than people on treatment with a CD4 count above 650.

Together, these findings suggest that starting treatment earlier may result in a better CD4 increase, and greater protection from illness.

Current guidance has not been changed in light of these studies but is being reviewed to weigh up the costs and benefits of earlier initiation of treatment.

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.

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.