European researchers develop method of calculating short-term risk of HIV disease progression

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A new HIV risk score can accurately calculate the short term risk of HIV disease progression, according to researchers who have tested it in a cohort of 5150 HIV-infected people. The research is published in the September edition of AIDS.

The researchers hope the scoring system – which will soon be available on the web – will make treatment decisions easier for both patients and clinicians.

Other prognostic HIV scores have been developed but have tended to be designed to predict long-term clinical progression in patients before they have started antiretroviral therapy. They have also not used routinely measured lab values.

Glossary

person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.

body mass index (BMI)

Body mass index, or BMI, is a measure of body size. It combines a person's weight with their height. The BMI gives an idea of whether a person has the correct weight for their height. Below 18.5 is considered underweight; between 18.5 and 25 is normal; between 25 and 30 is overweight; and over 30 is obese. Many BMI calculators can be found on the internet.

disease progression

The worsening of a disease.

haemoglobin (HB)

Red-coloured, oxygen-carrying chemical in red blood cells.

intravenous

Injected into a vein.

The new tool, called the EuroSIDA risk score, has been designed to be used in people already on anti-HIV treatment and calculates the risk of disease progression in the short-term, for example three, six or twelve months.

The researchers derived the risk score by studying the EuroSIDA study population, a group of 14,262 HIV-infected people in 31 European countries plus Israel and Argentina.

They identified 4,169 people for whom there were enough data to input into the risk score. This included those for whom it was possible to calculate the CD4 cell slope before starting antiretroviral drugs and who:

  • Had started HAART between 1997 and 2005.
  • Had a CD4 cell count and viral load in the six months before starting anti-HIV therapy.
  • Had a record of haemoglobin and body-mass index (BMI).

The data showed there were 658 events which defined clinical progression in the 22,231 person years of follow up, giving a incidence rate of 3.0/100 person-years.

Current viral load and CD4 count, CD4 cell slope, haemoglobin level and BMI were all independent predictors of new AIDS events or death.

Other risk factors included age, becoming infected through intravenous drug use, having taken any antiretrovirals before starting highly active antiretroviral therapy (HAART) and having a diagnosis of AIDS before starting HAART.

These factors were combined to come up with the risk score (of between 0 and 5) with patients being put into four categories: lower than 1.5, 1.5 to 2.99, 3.0 to 4.49 and 4.5 or above.

Those groupings then give a risk of developing an AIDS illness or death in three, six or twelve months.

For example, having a Euro-SIDA score of less than 1.5 means the chances of developing an AIDS event or illness is 1 in 801 at three months or 1 in 201 at twelve months.

Having a higher score, for examples 3.0 to 4.49 puts those risks at 1 in 63 and 1 in 16 respectively.

The researchers then validated the score, using a separate cohort of 5,105 patients from the Swiss HIV Cohort Study, and found consistent event rates in the four categories.

The developers of the Euro-SIDA score say it could be used by people on HAART and their clinicians to decide, for example, if risk was low enough to mean the patient could be seen for their next clinic appointment in six rather than three months time.

But it could also have useful applications in drug trials, either as an outcome measure when comparing different drugs, or as a way of making sure comparison groups in trials are similar at baseline.

The risk score is available online here.

References

Mocroft A et al. Short-term clinical disease progression in HIV-1 positive patients taking combination antiretroviral therapy: the EuroSIDA risk-score. AIDS 21: 1867-1875, 2007.