A blood test could reduce the inappropriate use of antibiotics for lower respiratory tract infections, reducing the risk of drug-resistant infections. The test measures blood levels of a chemical marker called procalcitonin, which is elevated with bacterial infections but not with viral infections.

In a recent Swiss study, researchers gave about half of 243 patients with lower respiratory tract infections standard care (physical exam, temperature check, and chest X-ray). The other half received standard care plus the procalcitonin-detecting blood test, which provided results within an hour.

In both groups, health care practitioners decided whether or not to prescribe antibiotics based on each patient's clinical condition. Practitioners caring for patients in the test group weren't informed of test results before they made prescribing decisions. Then the researchers disclosed the test results and advised practitioners to prescribe antibiotics only if levels of procalcitonin were above a certain value.

Before test result disclosure, the rate at which antibiotics were prescribed was about the same for each group. After disclosure, antibiotic prescriptions dropped by almost half. In all, 55 people in the test group received antibiotics, compared with 99 people in the control group.

Inappropriate antibiotic use is a primary cause of antibiotic resistance, a significant health care problem. Although promising for reducing antibiotic use, procalcitonin tests are currently too expensive and cumbersome for routine use.

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