Urine test could become early detection device
Urine test could become early detection device
But first, researchers must confirm HIV infection
Researchers have detected HIV antibodies in the urine of 24 low-risk people who tested negative for HIV in blood tests.
While these people appear to have been exposed to HIV, they may not have become infected with the virus. But the study’s findings also suggest that it is possible that one person in 1,000 who has tested negative for HIV in blood tests actually has been exposed to the virus and could become infected.
"At the very least, they’ve been exposed to HIV, and at the worst, they are infected with HIV," says Robert Stout, PhD, a biological chemist and president of Lenexa, KS-based Clinical Reference Laboratory, which conducted the study.
"Of great scientific interest is, if they are infected, how have they confined the infection to the urogenital tract?" Stout asks.
The study examined urine samples of 25,118 low-risk people who had given informed consent. They found that 24 samples had antibodies reactive to HIV, with companion blood samples that were HIV non-reactive. Research testing shows that IgA antibodies reactive to HIV were present in most of these urine samples. IgA is an antibody secreted by immune cells that provides protection for the mucosal surfaces of the body. The urine test was developed and is marketed by Calypte Biomedical Corp. in Berkeley, CA. The commercially available urine test has approval from the Rockville, MD-based Food and Drug Admini stra tion and currently is used on a limited basis.
The study will be presented at the annual American Association of Clinical Chemists meeting in New Orleans on July 25-29.
Explaining the findings
Here are three possible scenarios for what the findings mean:
• These individuals were exposed to the virus but may be immune to the virus and avoid any infection.
• They were exposed to the virus and are infected at a level that cannot be detected through current blood tests.
• They were exposed to the virus, harbor the virus in their urogenital tract, and may one day become systemically infected.
HIV blood tests screen for the IgG antibody, which is present in concentrations 10-20 times that of IgA. The IgA HIV test is currently used for research purposes only. The medical community has overlooked the urine test despite its potential research and clinical benefits, Stout says.
"We’ve always predicated our detection of HIV infections on IgG antibodies," Stout says. "I think we’ve overlooked one additional class of antibody that might be present, and it’s coming around full circle now for researchers to look for the presence of antibodies in non-serum fluids, such as urine."
Stout’s laboratory will conduct molecular tests on 10 of the urine samples over the next six months to see if the subjects’ urine samples contain HIV genetic material. If genetic material is found, these individuals are probably infected with HIV in their urogenital tract. Researchers can only speculate whether the virus could later spread to their blood and other parts of their bodies.
"What we have discovered is that some serum HIV-negative individuals have antibodies to HIV in the urogenital tract that typically are produced after an infection," Stout says.
When a person is exposed to HIV through sexual activity, it’s possible the virus and antibodies to it would appear in the urogenital tract before spreading to the bloodstream, Stout explains. This is one possible explanation for how someone could be infected with the virus and have no signs of it when given a blood test.
If the urine findings are correct, it could have a significant impact on health care clinics that offer screening for HIV because they then could have a tool that would detect HIV infection at a much earlier stage than what the blood test permits.
Screen for high-risk individuals
The urine test could be a way to screen high-risk individuals. If they are found to have HIV antibodies and infection, they could be given highly active antiretroviral therapy (HAART) before the infection becomes systemic, possibly even clearing their bodies of HIV, Stout says.
The study also examined urine samples of 128 high-risk individuals who had tested negative for the virus in the blood test. It found 10 incidences of HIV exposure in that group.
However, Stout says the urine test so far only establishes exposure to the virus. "We have to answer the question: Are these people carrying the infection?" he says.
Some long-term carriers of HIV have had the infection for 15 years or more and still have not progressed to AIDS. Stout says the study and use of the urine test could begin to explain why some people seem to be immune to the disease.
"But it’s premature to go down that line until we’ve established whether or not these people are infected," he adds.
The urine test is a relatively inexpensive way to detect HIV exposure, costing about $10,000 per 1,000 samples, Stout says.
Calypte officials say they sell the urine test to laboratories for $3 per sample.
By contrast, to screen 1,000 people for HIV using the molecular test would cost $100,000, Stout says.
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