A splash of pee could reveal bladder cancer.

Using a proof-of-concept urine test that decodes RNA molecules, it’s possible to pick out patients with the disease, scientists report October 2 in Nature Medicine . Because urine is in direct contact with bladder tumors, it’s “a very attractive fluid” to look for this type of cancer, says Stanford University oncologist Maximilian Diehn. The technology, still in its infancy, offers a glimpse of what future screening tests might entail.

Today’s liquid biopsies for cancer, which examine bodily fluids rather than tissue samples, largely focus on finding DNA that tumors shed into the blood. Diehn’s lab sought a different stream of information. The researchers analyzed RNA, DNA’s molecular cousin. RNA isn’t as stable as DNA, so it hasn’t been researchers’ top target. But it carries info that DNA lacks, such as which genes are turned on.…