An expert has revealed a simple “finger trick” that could help uncover respiratory tumours.

According to Bupa UK’s oncology nurse advisor Emma Norton, people can do this by bringing the nails of their index fingers together as if making the top of the heart.

A diamond-shaped gap should be visible between the nails, Norton said. If this is missing, it could be a sign of finger clubbing or a deformity of the fingers and fingernails, which may indicate serious diseases such as lung cancer.

The symptom occurs in 35 percent of people with lung cancer, according to Cancer Research UK.

“The test is used by medical professionals as a partial method of confirming conditions, but you can also do the test yourself, and it only takes a few seconds,” Norton said.

“If you can’t see any kind of gap beneath your nail beds, this means your fingers are clubbed.”

study by researchers at the University of Leeds found that tumour in the lungs may lead to the overproduction of a fatty compound called PGE2, which results in clubbing.

“There are benign cases of clubbing, where it isn’t associated with other illnesses, but particularly because of the link to lung cancer, it is generally regarded as rather sinister,” said Professor David Bonthron of the Leeds Institute of Molecular Medicine.

Norton recommends that people who do the test and uncover clubbing need to see their GP as soon as possible.

This article originally appeared on Over60.