HIV test misdiagnosis: How indeterminate Western Blot results can be misdiagnosed.
I Was Misdiagnosed With HIV
Health and medicine explained.
April 3 2013 4:19 PM

The Week I Had HIV


A staff member at the AIDS Service Center of New York City (ASC/NYC) holds an OraQuick Advance Rapid HIV-1/2 Antibody test kit.
A staff member at the AIDS Service Center of New York City (ASC/NYC) holds an OraQuick Advance Rapid HIV-1/2 Antibody test kit at ASC/NYC's lower Manhattan headquarters July 3, 2012.

Photo by Mike Segar/Reuters


Mark Joseph Stern Mark Joseph Stern



I realized it now. “Your ELISA test went up to positive,” Dr. Smith told me, “so it triggered a Western Blot, and that came back indeterminate. Let me tell you what that means. You’re probably early on in your infection, so it’s not showing completely yet. But these results, in my experience, always indicate HIV positivity. Why don’t you come in tomorrow morning and we can get an RNA test and a confirmation?”


“A confirmation,” I asked, “that I have HIV?”

“Yes,” the doctor said. “We should definitely assume right now that you have HIV.”

This assumption would be proven false after a week—a week of anxiety, anger, and, most of all, confusion. My HIV test showed indications of early infection, signs portentous enough to prompt a doctor to diagnose me on the spot. Yet as I received more tests and more information, it became increasingly clear that Dr. Smith’s verdict was a misdiagnosis—that I did not have HIV.

How can a test so common, so regulated, so accurate fail? How could I, a healthy adult with virtually no risk of infection, be misdiagnosed with HIV? And if it could happen to me, who else could it happen to?

Most HIV tests don’t test for HIV. Rather, the primary diagnostic tool, an immunoassay, tests for antibodies that react to HIV. (Earlier generations of immunoassays were called ELISAs, pronounced “Eliza”; most immunoassays today are a newer generation called EIAs, but many doctors still call them ELISAs as shorthand.) The immune system floods the body with these antibodies soon after HIV infection as it attempts, in vain, to fight off the virus.

If an immunoassay test turns up HIV-related antibodies, it’s considered “reactive.” But a reactive immunoassay is not considered proof of an HIV infection. It must be followed up with a confirmatory test, usually a Western Blot. These tests also search for antibodies, but rather than turning “reactive” or “nonreactive,” they detect about 10 different “viral bands.” These bands are specific antibodies that bind to different components of the virus. If a Western Blot turns up two or more reactive bands, the patient is considered HIV-positive. If it turns up one band or several “equivocal” bands, the test is considered “indeterminate” and should be run again in about a month.

That monthlong wait speaks to perhaps the most insidious aspect of the AIDS virus: It hides. After infection, the virus conceals itself completely for about 10 days—the so-called “eclipse period.” (A person in the eclipse period is almost certainly not infectious.) Once that phase ends, the virus begins attacking the immune system, provoking the antibodies detectable by immunoassays and Western Blot tests. Yet the process of producing antibodies takes time, and so there is an additional “window period” between antibody production and immunoassay reactivity. For today’s fourth-generation tests, the time between infection and detectability is about 15 days; for third-generation tests, some of which are still used, it’s 25; second- and first-generation tests need 50 to 60 days of infection to detect any antibodies. Western Blots require about two months of infection before turning positive.

This period of undetectability also happens to be the most highly infectious phase of the disease. Between 30 and 50 percent of all HIV transmissions occur during the window period. Thus, it presents perhaps the greatest challenge to combatting HIV: How can a highly infectious person be stopped from spreading the virus if he can’t know he has it?

I received a third-generation immunoassay, which measured an antibody level of 1.23, just faintly reactive. (A level below 1.00 is considered nonreactive.) Following protocol, the lab then ran a Western Blot, which turned up “indeterminate.” Dr. Smith told this to me when I went into the office the following morning. I asked for further explanation.