Women infected with H.I.V. may be at a more advanced stage of infection and at a higher risk of developing AIDS than men with identical results on certain blood tests, researchers are reporting today.
The researchers suggest that official treatment guidelines, used for both sexes even though they are based on research only in men, should be changed to recommend earlier treatment for women.
But other researchers have said changing treatment guidelines now would be premature.
The recommendations are based on a study conducted at the Johns Hopkins School of Public Health, in Baltimore, and are being published today in The Lancet, the British medical journal.
The study's researchers measured virus levels in the bloodstream, or "viral load," a major factor in deciding when a patient should begin treatment with antiviral drugs. The researchers found that at a given stage of infection, a woman's viral load will be lower than a man's even though her immune system has sustained just as much damage as his.
The researchers do not know why, they said. But they warned that doctors who used the viral load as a benchmark might be misled into thinking the woman was healthier than she really was.
The study adds fuel to a larger debate among AIDS experts about the best time for people with H.I.V., the virus that causes AIDS, to begin taking antiviral drugs. Combinations of those drugs have led to such stunning drops in the AIDS death rate that many researchers think patients should be treated as soon as possible to suppress H.I.V. and prevent damage to the immune system.
But other doctors, concerned about dangerous side effects of treatment and the ability of H.I.V. to become drug resistant, say they think patients who are not ill should postpone treatment for as long as possible.
"This is the most contentious issue now," said Dr. Jerome Groopman, an AIDS expert at the Harvard Medical School. "Do you watch and wait, fearful that you'll burn your bridges, or do you hit the virus early and hard? The answer now is no one knows. This paper adds another dimension to the debate, makes it more vexing."
Guidelines issued this year by the United States Public Health Service recommend starting treatment in both men and women when the viral load climbs to 10,000 copies of H.I.V. per milliliter of blood. That level is generally taken as a sign that the immune system is losing ground to the virus.
But a viral load of 5,000 in a woman may be just as bad as a reading of 10,000 in a man, according to today's study. A woman with half the viral load of a man has the same risk of developing AIDS as that man, and if the two have the same virus level, the woman is more likely to develop AIDS, the Johns Hopkins researchers found.
Their conclusions were based on a study of 650 male and female drug users who were infected with H.I.V. Many had been research participants since 1988, with frozen blood samples in storage that allowed scientists to study virus levels over the years and see how they correlated with the patients' health.
A woman with the same viral load as a man had a 60 percent greater risk of developing AIDS, said Dr. Homayoon Farzadegan, a Johns Hopkins associate professor of epidemiology who directed the study.
"Viral load in women is a different animal than it is in men," Dr. Farzadegan said in an interview. "If you take the data from men and apply them to women, we feel that women are going to be undertreated, or get treatment too late."
Other researchers agreed that the Johns Hopkins findings were important, but said that they thought it was premature to let the results influence treatment guidelines.
Dr. Kathryn Anastos, who studies AIDS at the Catholic Medical Centers in Jamaica, Queens, said: "The study raises the question of whether we should consider gender in establishing treatment guidelines. But it doesn't answer the question."
It would be valuable to find out why virus levels differ in men and women, Dr. Anastos said, adding:
"For years we wondered whether there were gender differences in how AIDS progressed, and we went through a period in which we thought gender did not make a difference. Now that we can see a difference in something as concrete as the viral burden, it has to give us more intellectual humility and make us realize we don't really know what the virus is doing in there."
Dr. Ruth Greenblatt, who heads an AIDS clinic for women at the University of California at San Francisco, said, "This will not be the only study to find this difference in viral load."
Dr. Greenblatt and Dr. Anastos, with researchers at other medical centers, have recently made similar findings, which have not yet been published.
"It does seem like women run lower viral loads than men at the same state of progression," Dr. Greenblatt said.
But whether starting treatment earlier would help those women is not known, she said, adding, "The way to test that would be to do a study and look for a difference in outcome."
Several other studies of sex differences in viral load are under way, Dr. Greenblatt said, and may help to resolve the question. In the meantime, she said, "I don't want to alarm women or make them feel that the advice they're given based on viral load is somehow inadequate."
Dr. Greenblatt said she handled the uncertainty by discussing it with her patients and letting them decide when to begin treatment.
"When we don't know and the experts don't agree," she said, "my job is to explain it to patients."
Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said, "I really would not go so far as to say you need to modify the guidelines for women."
But Dr. Fauci said he would take the findings into consideration in treating female patients, and would let them know that in women with lower viral loads, H.I.V. infection might progress at a rate comparable to that in men with higher levels. Then, he said, he would try to help patients work through the pros and cons of treatment.
Dr. Anastos said she hoped that eventually a better understanding of the differences in H.I.V. infection in men women would lead to a better understanding of the disease and improved treatment.