CD4 counts and HIV Level Can Be Measured in Dried Blood

By Karla Gale

Whole blood applied to filter paper and dried can be used to measure CD4 lymphocyte counts and viral load of HIV-infected patients, new study findings suggest.

"Now that antiretroviral drugs are becoming available in developing countries, patients will need to be monitored for drug toxicity and resistance mutations," senior investigator Dr. Alimuddin Zumla, with University College London, told Reuters Health.

Even though flow cytometry is the standard method for measuring CD4 cell counts, he pointed out, it requires plasma separated from fresh blood. "But the majority of people in Africa live hundreds of miles away from centers" that have the necessary equipment.

To develop a more practical technique, he said, his group found a way to enumerate CD4 lymphocytes and to determine viral loads using dried blood samples.

According to their report in the November 1st issue of The Lancet, whole blood was obtained from 42 HIV-infected adults in Lusaka, Zambia. The results obtained with flow cytometry conducted the same day were compared with ELISA testing of 50 µL samples spotted onto filter paper, dried and stored for 30 days at room temperature.

Flow cytometry indicated CD4 counts ranging from 55 to 668 cells/µL (mean 289). With ELISA testing on the dried blood samples, CD4 lymphocytes averaged 347 cells/µL (range 120 to 800 cells/µL).

The researchers found that agreement between the two methods was much higher for samples with more than 200 cells/µL.

His group is in the process of standardizing and refining the procedure for more accuracy, Dr. Zumla said, and hopes to conduct more field trials soon.

"We are doing a similar thing for viral load quantification, and the results are looking good," he added. "The correlation between plasma viral load and whole blood is even better than that for CD4 counts."

11/05/03

Lancet 2003;362:1459-1460.