More than 80 percent of patients whose kidney cancer isn’t discovered until after it has spread will die within five years, and current tests for the disease are dependent on whether a patient has started showing symptoms. But a study published Thursday in the journal JAMA Oncology shows that  measuring protein levels in urine may help doctors identify the disease early.

“By and large, patients don’t know they have kidney cancer until they get symptoms, such a blood in the urine, a lump or pain in the side or the abdomen, swelling in the ankles or extreme fatigue. And by then, it’s often too late for a cure,” principal investigator Jeremiah J. Morrissey, an anesthesiology professor at Washington University, said in a news release. “Metastatic kidney cancer is extremely difficult to treat, and if the disease is discovered after patients have developed symptoms, they almost always have metastases.”

Researchers identified two protein biomarkers— aquaporin-1 (AQP1) and perlipin-2 (PLIN2)— that were more than 95 percent accurate in detecting early-stage kidney cancers. The tests also didn’t result in any false-positives caused by non-cancerous kidney disease.

“These biomarkers are very sensitive and specific to kidney cancer,” senior author Evan D. Kharasch, an anesthesiology professor at Washington University, said in the news release.

Study authors analyzed urine samples from 720 patients at Barnes-Jewish Hospital, in St. Louis, who needed abdominal CT scans but weren’t suspected of having kidney cancer. Doctors used the scans to tell whether the patients had kidney cancer. Authors also analyzed samples from 80 healthy individuals and 19 patients already diagnosed with kidney cancer.

Patients who had been previously diagnosed with kidney cancer showed elevated levels of both of the proteins, while none of the healthy people had elevated levels of either protein. Three of the 720 patients who had elevated levels were later diagnosed with the disease.

“Each protein, or biomarker, individually pointed to patients who were likely to have kidney cancer, but the two together were more sensitive and specific than either by itself,” Morrissey said in the news release.

The presence of non-cancerous kidney disease or other types of cancer did not result in elevated levels of the proteins, so the urine test may also have the potential to help doctors identify when a patient doesn’t have kidney cancer, researchers noted. Doctors today can use CT scans to detect whether a kidney tumor is present, but invasive surgery is the only way to tell whether that tumor is cancerous, Kharasch said.

According to the news release, Kharasch and Morrissey are aiming to develop a kidney cancer test similar to mammograms or colonoscopies, which have helped improve early diagnosis rates  for other cancers.