A blood test could help doctors determine whether antibiotics are needed for common respiratory infections and may reduce the over-prescribing that creates drug-resistant germs, new research suggests.
About 75 percent of all antibiotics are given for lower respiratory tract infections such as bronchitis and pneumonia. Most of these infections are caused by a virus, not bacteria.
Experts say antibiotics are not only useless against viral infections, but also help bacteria evolve defenses against drugs.
The new test, described this week in The Lancet medical journal, measures blood levels of a chemical marker that is elevated in bacterial infections but not so high when the cause is a virus. It yields results within an hour.
"This looks very promising,'' said Roy Anderson, an expert on antibiotic resistance at Imperial College in London. "Cutting the overuse of antibiotics is crucial to combatting antibiotic resistance.''
Anderson, who was not connected with the study, said current tests are too expensive and cumbersome to be practical for use by family doctors.
"What you want eventually is a kind of quick and easy dipstick test that can tell you right away. It needs refining, but something like this could evolve into a dipstick where it turns one color for a positive and another color for a negative,'' he said.
The study involved 243 patients treated at the University Hospital in Basel, Switzerland, for suspected lower respiratory tract infections. Half the patients got the standard care, which usually included a physical examination, temperature check and chest X-ray, while the others got standard care plus the blood test.
In both groups, the decision on prescribing antibiotics was left to doctors. However, in the blood test group, the doctors had to decide on prescribing antibiotics before learning the blood test results.
After the blood test results were revealed, the researchers then advised the doctors to prescribe antibiotics only if the blood level of the chemical marker, called procalcitonin, was above a certain level.
The rate of antibiotic prescriptions foreseen by the doctor was similar in both groups before the blood test results were disclosed. But once test results were known, antibiotic prescriptions dropped almost in half.
A total of 99 patients in the comparison group got antibiotics, compared with 55 in the blood test group. Antibiotics were given to 22 patients with a blood test showing low levels of the chemical marker.
Doctors often prescribe antibiotics to people with severe viral infections because viruses can damage the airways enough to encourage a subsequent life-threatening bacterial infection.
"Importantly, withholding antibiotic treatment was safe and did not compromise clinical and laboratory outcome,'' said the study, led by Dr. Beat Muller at the University of Basel.
Dr. Marc Siegel, a professor of medicine at New York University School of Medicine, said the study convinced him the procalcitonin marker may help doctors, but larger studies are needed to determine if it is safe to withhold antibiotics from high-risk patients.
The danger of missing a severe or progressing bacterial infection is too great to rely solely on the blood test, Siegel said.
"You worry about antibiotic resistance, but you also worry about patients dying,'' he said.