A quick test for bacterial infections on a single drop of blood may help reduce the overprescription of antibiotics, according to a new review. Danish researchers found that doctors who used the C-reactive protein test – the only such on-the-spot kit available to GPs – gave out fewer antibiotics. According to The Guardian, the test involves testing a drop of blood from a patient’s finger and takes about three minutes.

C-reactive protein acts as a “biomarker” of inflammation; low levels may effectively rule out serious bacterial infection and therefore avoid the unnecessary use of antibiotics.

Antibiotics treat infections caused by bacteria, but not those caused by viruses. Most patients with respiratory infections suffer from viral infections such as a cold. However, because doctors usually have no easy way of knowing whether the infection is bacterial or viral, they err on the side of caution and prescribe antibiotics.

The findings, published in the Cochrane Library, were based on six trials involving 3,284 people, most of whom were adults. Overall, 631 out of the 1,685 people who took the test were prescribed antibiotics, compared to 785 out of the 1,599 people who did not take it.

The review cautioned that the results varied considerably between studies, making interpretation of the findings more difficult. Still, researchers were positive.