PARIS (AFP) - One of the biggest obstacles hampering the campaign to distribute anti-HIV (news - web sites) drugs across Africa may have been overcome by a technique that is simple, rugged and cheap, a study says.

Using just ordinary filter paper and inexpensive commercially-available reagents, researchers report they were able to replicate tests normally carried out by sophisticated machines to evaluate a patient's immune health.

"The results are wonderful. They help the search for something that is inexpensive, reliable and effective," lead author Alimuddin Zumla, a professor at the Centre for Infectious Diseases and International Health at University College London, told AFP.

Carrying out a count of so-called CD4 immune cells is vital for figuring out whether an individual is responding to antiretroviral drugs.

In rich countries, CD4 counts are carried out by a flow cytometer, a machine which counts cells as they pass through a laser beam.

These gadgets are expensive to buy -- around 35,000 dollars each -- and need to be staffed and maintained by trained technicians. Blood samples have to be fresh, which in practical terms means that the patient has to be within a travelling distance of two hours from the lab.

All that represents a crippling burden for poor, underequipped African countries that are bearing the brunt of the global HIV/AIDS (news - web sites) epidemic.

Writing in next Saturday's issue of The Lancet, Zumla's team took blood from 42 HIV-infected volunteers in Zambia.

The blood was allowed to dry on filter paper and was then sent off to a laboratory, which used chemicals known as buffers to leach out the blood.

The blood was then put through a CD4 count using a far cheaper, although less precise, antibody technique called the ELISA process.

The same blood samples, carefully refrigerated and rushed to a specialist lab, were also tested by a flow cytometer, the "gold standard" for accuracy.

The rule of thumb with CD4 counts is that people with less than 200 cells per microliter of blood have a damaged immune system and are a candidate for antiretrovirals.

These are the triple "cocktail" of HIV-suppressing drugs that have revolutionised life for patients in rich Western countries.

They are now progressively entering poorer countries, thanks to swingeing price cuts by pharmaceutical companies and the prospect of competition by "generic" copies of patented drugs.

The filter paper/ELISA method scored well in comparison with the flow cytometer. It was not as precise -- the variation was on average about 20 percent -- but that difference narrowed when a patient was above the important 200 count.

To see whether the dried blood could be reconstituted and accurately tested, the team kept the samples at room temperature for 30 days.

The technique has still to be refined, but it is highly promising. It would mean that a small local clinic can take a blood sample from HIV patients, dry them on filter paper, batch them and send them by post to a regional laboratory to carry out the CD4 count, Zumla said.

A CD4 count by cytometer typically costs 20 to 40 dollars, "which is about the annual per-capita health spending in poor African countries," he said.

"This way would cost only 50 cents to a dollar, including the lab technician's salary."

AIDS has claimed 20 million African lives in 22 years and 30 million others have HIV or the full-blown disease, nearly three-quarters of the global tally.

Some five billion dollars are needed to fund the World Health Organisation's "Three by Five" initiative, of providing antiretrovirals to three million seriously ill people with HIV by the end of 2005. More than two million of them are Africans.