If you're diagnosed with HIV and have a CD4 cell count above 500, should you start antiretroviral (ARV) therapy immediately? An Australian study suggests that even though there may be some immunologic benefits to starting therapy earlier than is currently recommended—once the CD4 count drops below 500—the jury is still out on whether this translates into important clinical benefits.

Despite more than 25 years of ARV research and the successful development of more than two dozen medications, scientists have not been able to determine the ideal time to begin therapy. Several studies have concluded that HIV treatment is best started before a person's CD4 count falls below 350.

Some studies, conducted during the past five years, suggest that starting therapy even earlier—when the CD4 count is between 350 and 500—further increases the chances of disease-free survival. Less is known about the potential benefits of initiating therapy earlier still, when the CD4 count is above 500. 

A large clinical trial, called the Strategic Timing of Antiretroviral Treatment (START) study, is being conducted to explore the safety and effectiveness of beginning treatment when the CD4 count is above 350 cells. Preliminary data, however, are not expected for at least another few years.

In the meantime, HIV-positive people and their health care providers are on the lookout for smaller observational and retrospective studies, such as the one recently published online by the Journal of Acquired Immune Deficiency Syndromes and based on data from Stephen Wright and his colleagues with the Australian HIV Observational Database.

Wright's group looked at the outcomes of 432 people living with HIV who started ARV therapy with a CD4 count above 350 and had been followed for six years (72 months). For their analysis, the researchers divided the study volunteers into three groups: those who started treatment with a CD4 count between 350 and 500, those who started treatment with a CD4 count between 501 and 650 and those who started treatment with a CD4 count above 650.

Twelve months after beginning treatment, all study volunteers had CD4s above 500. Average CD4 counts, after a year of ARV therapy, were 596 among those who started with CD4s between 250 and 500, 717 among those who started treatment with CD4s between 501 and 650, and 881 among those who started treatment with a CD4 count in excess of 650.

After six years, CD4 counts were comparable between the three groups. Among those in the lowest pre-treatment CD4 group, the average CD4 cell count was 689. In the middle- and high-pretreatment CD4 groups, the average CD4 count after three years was 746 and 742, respectively.

Wright's team also sought to determine whether there was a survival advantage between the three groups. Comparing their Australian data with those of another study, the researchers documented a modest 8 percent expected reduction in the risk of death among those who started treatment with more than 650 CD4s and a 4 percent expected reduction in the risk of death among those who started treatment with 501 to 650 CD4s, compared with those who started treatment with CD4s between 350 and 500. It is important to note, however, that the estimated number of deaths in these three groups were very low, which translated into very small differences in the absolute risk of death between those in the two highest CD4 groups compared with those starting with CD4s between 350 and 500.

“Our analysis suggests that patients who start [ARV therapy] at CD4 counts [greater than] 650 have better preserved immune function, but only to a relatively modest degree,” the authors conclude. “Furthermore the extent to which this might be expected to result in better clinical outcomes is uncertain.”