A negative rapid flu test did not necessarily mean that the patient did not have the 2009 H1N1 influenza, said experts at Baylor College of Medicine and Texas Children's Hospital in a report that appears online today in the journal Pediatrics.
"The test was specific. That means that if it was positive, it's very likely that the child truly had influenza. However, the test was not very sensitive. A negative test did not mean the child did not have the flu," said Dr. Andrea T. Cruz, assistant professor of pediatrics – emergency medicine at BCM and Texas Children's Hospital and lead author of the study.
Don't rule out H1N1
The study compared more than 3,000 rapid influenza diagnostic tests for H1N1 influenza collected over a four-month period to results from the two long-term tests considered the gold standard: real-time reverse-transcriptase polymerase chain reaction and viral culture results. The reverse-transcriptase polymerase chain reaction test uses cutting-edge molecular techniques to identify the virus. The other test grows the virus in the laboratory. The rapid influenza test finds an influenza-specific antigen or protein on the surface of the virus.
"We wanted to see how well the rapid influenza diagnostic test did in diagnosing H1N1 because these tests were not created with H1N1 in mind," said Cruz. "We wanted to provide physicians with advice on what to do and what not to do."
Their answer is that physicians should not rule out H1N1 because of a negative rapid influenza diagnostic test, said Cruz. "Physicians should not base antiviral treatment on the results of the rapid influenza diagnostic test."
Begin antiviral treatment
That means that even when there is a negative rapid test, physicians should begin antiviral treatment of high risk patients with flu symptoms. Those at high risk include patients with a depressed immune system because of disease or treatment for cancer, transplant or other disorders, and patients with chronic lung problems.
Others who took part in the study include Dr. Gail J. Demmler-Harrison, Dr. A. Chantal Caviness, Dr. Gregory J. Buffone and Dr. Paula A. Revell, all with BCM and Texas Children's Hospital.