Dear Dr. Jeff: So what's the deal with HIV testing? What are the different kinds of tests? How accurate (and expensive) are they? What's the difference between confidential tests and anonymous tests? What does the school offer? Who needs to be tested? Where are nearest testing facilities that offer rapid HIV testing? Is the test accurate if I've had sex recently? If I haven't shown any symptoms do I need to be tested?
?A.S. (Anonymous Student(s))
Dear A.S.: Lots of good questions about an important topic!
HIV tests can be categorized in a number of ways. First, there are screening tests, as opposed to "clinical" tests. The former are meant for people who don't know if they've been exposed to HIV, the latter for those who know they've already likely been infected. Screening tests look for antibodies to the virus, an indication of prior exposure. "Clinical" tests, on the other hand, might measure actual viral load or other clinical correlates of active HIV infection.
Screening tests look for antibodies to HIV most commonly in blood, saliva, or urine. In general, screening tests are "staged." They start off with a less expensive test that's very sensitive but less specific. That means that they will miss extremely few, if any, true positives?the trade-off being that they will read as positive some number of true negatives. For HIV testing, this initial stage is usually done by an "ELISA" ("Enzyme-Linked Immunosorbent Assay"). A negative result, for an ELISA done at the appropriate time (more on this later!), is virtually 100 percent accurate. All positive results are confirmed (or refuted) by a much more specific, and much more expensive, "Western Blot" assay. A positive ELISA followed by a negative Western Blot will be reported as negative.
HIV screening can be done anonymously, confidentially, or, like we do at the Health Center, somewhere in between. Completely anonymous testing is available in the community, for instance, through Merrymeeting AIDS. At anonymous test sites, your identity is unknown and remains unrecorded at every step of the process. The idea is to encourage HIV screening amongst those who do not want to have the fact that they're even taking the test, never mind the actual test results, ever recorded anywhere in any way. In confidential testing, your name is on the specimen and on the test results, and both are properly handled with the same respect for privacy and confidentiality as the rest of your medical records.
At the Health Center, we can't pretend that we don't know who you are, so we've tried to come up with the next best thing. When we send off specimens to the state lab, they are labeled only with a numeric code, and you alone are the keeper of that code. The consent form you sign, and your test results, are kept in a special locked file, separate from your medical record. When you come in to pick up your results, you take them and your consent form with you, or we shred them. Nothing goes into your chart?not even an indication that you were ever tested. And HIV testing at the Health Center, like all STD testing done at the Health Center, is free of charge. Your insurance policy (through Bowdoin or your parents) will not be billed for these tests.
"Rapid" screening tests for HIV have been available for a few years now, and we offer both rapid and conventional tests at the Health Center. Rapid-test HIV ELISAs screen blood or saliva and give on-site results in 20 minutes. The rapid-test ELISAs are very slightly more sensitive for blood than saliva, and this difference can be somewhat more significant when testing individuals with low exposure risk.
We send nearly all of our conventional HIV ELISAs to the State labs, where they're processed anonymously. If someone needs to have his or her results identified by name (for instance, for a Peace Corps application), then we send the test off to a commercial lab. The state labs take about a week to return the test results. Commercial labs generally take only a few days.
In all cases, whether rapid-test or conventional, and whether saliva-, blood-, or urine-based, positive ELISA results always need to be confirmed by Western Blot. Getting negative results from a rapid-test, without a needle stick, and after only 20 minutes of waiting, may certainly qualify as near-instant gratification. Waiting many more days for definitive results, however, after a "positive" rapid-test screen, would obviously prove to be extremely stressful.
All HIV screening requires pre-test and post-test counseling by a specially trained provider. As I hope I've already made clear, these tests have a number of often complicated nuances, and decisions about which test is best, and about when and how best to take them, can sometimes be quite challenging. This is especially true with the issue of timing.
It takes at least a few weeks after an infectious exposure to HIV to develop antibodies to the virus. Antibody levels that can be detected by screening ELISAs may take even longer to develop: up to three months for about 95 percent of us. If you want virtually 100 percent certainty with an ELISA, you need to wait six months after a possible exposure to be tested. A negative ELISA means that you almost certainly were not exposed to HIV six months ago or before. If you're looking for that 100 percent reassurance about something that may have happened in the last six months, you can't get it from a screening ELISA.
In its initial, acute phase, HIV infection can cause any number of non-specific symptoms, like fever, fatigue, body aches, sore throat, and swollen lymph glands. In this initial phase, HIV may be indistinguishable from a host of other far more common viral infections. It may also be asymptomatic, causing no signs or symptoms whatsoever.
If you are concerned that you may have been recently exposed to HIV, and have no symptoms, you should see a health care provider and determine whether you can reasonably wait the three or more months for ELISA screening. If you are concerned that you may have recently acquired HIV, especially if you do have symptoms, you should see a health care provider and determine whether you should undergo clinical testing with one of the more complicated, more sensitive, and, needless to say, more expensive modalities, like PCR. These "clinical" assays can detect minute levels of the virus itself in your blood, well before your body has made enough antibodies to register on an ELISA.
So, A.S., a lot of good questions, and a lot of complicated material to cover in just a couple of pages.
We're all happy to talk this over in detail with you at the Health Center. Just call for an appointment. But if you're looking for HIV screening, you'll need to make that appointment by May 5. Because of possible delays in getting HIV test results back, and because we want to make sure we can properly cover the post-test counseling, we won't be offering any HIV testing this semester after the 5th.
Be well!
Jeff Benson, MD
Dudley Coe Health Center