The meta-analysis of RIDTs included 159 studies that assessed the accuracy of 26 commercially marketed RIDTs; 119 of the studies compared one or more RIDTs against either of the two reference standards for influenza infection, viral culture, or reverse transcriptase-polymerase chain reaction. The analysis showed that specificity rates ranged from 51% to 100%, and that sensitivity rates ranged from 4% to 100%. The pooled sensitivity was 62%, and the pooled specificity was 98%, reported Dr. Caroline Chartrand, a pediatrician at CHU Sainte-Justine in Montreal, and her associates.
"Overall, RIDTs have high specificity, with modest and highly variable sensitivity," the authors concluded. "This means that a positive test is unlikely to be a false positive result." In the presence of a positive RIDT result, "a clinician can confidently make the diagnosis of influenza and begin appropriate infection-control measures and antiviral therapy, if indicated, while forgoing unnecessary additional diagnostic testing and antibiotic prescription. However, a negative RIDT result has a reasonable likelihood of being a false negative and should be confirmed by other laboratory diagnostic tests if the result is likely to affect patient management."
The analysis also showed that RIDTs performed better in children than in adults, with approximately 13% higher sensitivity in children. "This is plausible because young children have higher viral loads and longer viral shedding than adults," the authors said. RIDTs also showed higher sensitivity for detecting influenza A compared with influenza B.
"Overall, no commercial brand of RIDT seemed to perform markedly better or worse than the others, but this finding should be interpreted cautiously because head-to-head comparisons were not done in most studies. Administration of the RIDT by personnel other than a trained laboratory technician does not seem to adversely influence the performance of these tests," they added.
"The most important advantage of RIDTs is their rapid turnaround time. RIDTs fill a void at the point of care that no other test is likely to fill in the near future. As long as clinicians understand the limitations of RIDTs, namely that a negative result is unreliable and should be confirmed by using culture or RT-PCR, RIDTs could enable clinicians to institute prompt infection-control measures, begin antiviral treatment in high-risk populations, and make informed decisions about further diagnostic interventions," the authors concluded.
The meta-analysis results "support the notion that a positive rapid test result is much more helpful to the clinician than a negative result," commented Dr. Peters. "Positive test results can prompt early, appropriate initiation of neuraminidase inhibitor therapy. A negative result may occur in an influenza-infected patient at high risk for severe disease, especially in adults who shed less virus [than children] when infected. Clinicians should be especially suspicious of negative test results at times when they are seeing a lot of influenza disease, and they should be prepared to initiate early neuraminidase inhibitor therapy when their clinical suspicion for influenza is high despite a negative test result," Dr. Peters said.
Dr. Schünemann and his associates, Dr. Chartrand and her associates, and Dr. Peters said that they had no disclosures.