Poor people, drug users and minorities were most likely to scrimp on care due to the need to work or spend money on basic necessities, the study found.
The researchers concluded that more resources must be devoted to supporting patients' non-medical needs in order for all HIV-infected people to gain the benefits of improved therapies.
"We found that an enormous number of people are not receiving medical care that could help extend their lives," said Dr. William Cunningham, lead author of the study, which is published in the December edition of the journal Medical Care.
"Our findings may only be the tip of the iceberg since we could only study people with some connection to the health care system," said Cunningham, an assistant professor at the University of California, Los Angeles, schools of public health and medicine.
The study, conducted by UCLA, the Rand Corp. and eight other institutions, involved interviews of 2,864 adult HIV patients who were selected in 1996.
Researchers concluded that a third of U.S. HIV patients, about 83,000 people, went without medical care or postponed it at least once in a six-month period.
The patients said that paying for food, clothing and housing forced them to go without care. Sometimes they delayed getting care because they were without transportation, unable to get out of work or too sick to visit a doctor.
Such patients were more likely than other HIV patients to have never received the latest antiretroviral therapy. Those who postponed care were more likely to use an emergency room for care best given in a doctor's office.
The problem also worked in reverse 8 percent of those interviewed said they sometimes had to go without food, clothing or housing because they needed to spend money on HIV care.
Vanessa Baird, acting chief of the California Office of AIDS, said the study's findings were no surprise to those who work with HIV patients.
"I think it happens with people who are sick, period, who are sometimes living on the margins, where the choice of accessing something means giving up something else," she said.