Don’t Rely on Rapid Swine Flu Tests: Your Health May Be in Danger

United States health officials report that physicians can not rely on the results of the swine flu rapid tests as they miss many infections. This was reported after they evaluated three kits. The tests are not definitive. According to Michael Shaw, associate director of laboratory science in the CDC’s influenza department, the rapid tests are designed to be performed in the doctor’s office and to offer results within about fifteen minutes. Rapid tests have been used for a couple decades, so they are not a new phenomenon.

Apparently the rapid tests do a better job of detecting the seasonal flu than the H1N1 swine flu. The USCDC reports that sensitivity to the H1N1 swine flu was only 40 to 69 percent.

Rely on the Clinician’s Judgment

Shaw advises that the rapid test is only one tool and should not be relied upon. He recommends that a clinician’s assessment of symptoms as well as his or her knowledge of the strains of virus circulating in the local area should be relied upon much more heavily than any rapid test. Shaw states, “There is no substitute for the judgment of the clinician.”

It is possible for a patient to test negative when he or she actually has the flu. However, positive results are accurate. "But a positive result only tells you it is flu, not what kind," Shaw said. "It could be seasonal; it could be the pandemic strain." This definitely should lead the physician to begin antiviral treatment though.

Recent Study Results

The August 7 issue of the CDC’s Morbidity and Mortality Weekly Report published results of a recent study. Three different commercially available rapid test kits that can identify influenza A and B antigens within about 15 minutes were tested. Sixty-five people that were known to have the swine or seasonal flu provided respiratory samples.

According to the CDC, the swine flu was only detected when the amount of the infection in the respiratory sample was high. This means that a large number of infections would be missed. Shaw reports that the most viruses are emitted shortly after symptoms occur, which makes early testing very important.

Tests Are Not Clinically Important

Anyone currently suffering from the flu has the potential of having H1N1 swine flu according to Dr. Marc Siegel, an associate professor of medicine at New York University Langone Medical Center in New York City. Therefore, tests are not clinically important.

Siegel agrees with the CDC that the diagnosis should be made be assessing the patient’s symptoms and the strains that are circulating. "I make the diagnosis on clinical grounds. I am comfortable doing that," Siegel said. "The test is just an adjunct. It's helpful if it's positive, but a negative flu test does not rule it out. Go by your clinical judgment."

A more definitive test would be helpful to identify the strain of flu and to help in early diagnosis of high-risk patients. Until that happens, physicians will have to rely on their ability to make a clinical diagnosis.