Doctors may be able to watch for kidney injury and protect patients by looking for protein in urine, researchers reported on Thursday.

Patients with the highest levels of protein, or albuminuria, had an almost five-fold increase in the risk of developing acute kidney injury, the researchers reported in the Journal of the American Society of Nephrology.

The cheap and easy test may provide a way to watch for kidney damage and improve upon the current method, called estimated glomerular filtration rate, the team at Johns Hopkins University in Baltimore said.

Acute kidney injury, common when people are in hospital, is seen in 1.6 percent of all hospital patients and occurs when kidneys suddenly lose the ability to filter waste products from blood.

Acute kidney injury can be reversible if a patient is otherwise healthy, but often results in chronic kidney disease and kidney failure requiring dialysis or a kidney transplant.

"It's potentially reversible, but not always. And the reason we worry so much about acute kidney injury is that it can lead to bad things in the future, put people at much higher risk for death, put them at risk for chronic kidney disease," said Dr. Morgan Grams, who worked on the study.

Grams and colleagues studied 11,200 patients, looking at their medical records. They had the albuminuria test as part of their care.

Even low levels of albuminuria indicated that a patient would go on to develop acute kidney injury, the researchers found.

Kidney injury can happen when patients receive medication or intravenous contrast dyes to make their internal organs visible during computed tomography or CAT scans or procedures on coronary arteries.

"Often it's a trade-off. You have to do a CAT scan, but you can try to minimize the amount of contrast that is given or give a better kind of contrast," said Grams.

Nearly 30 million Americans, or 10 percent of the population, have chronic kidney disease, says the American Society of Nephrology. More than 100,000 Americans are diagnosed with kidney failure each year, with diabetes the most common cause.

Doctors have a clear way to measure risk factors for chronic kidney disease. They examine levels of serum creatinine, a byproduct of muscle breakdown, in the blood. They adjust the measurement for demographic risk factors such as age, gender, and race.

"This misses a whole population of people who are at risk for acute kidney injury," Grams said.

There may be a genetic connection. Scientists at Decode Genetics in Iceland found a link between a single letter variation in the genetic code and concentrations of serum creatinine, the protein that indicates chronic kidney disease.

The finding could lead to better ways to treat and prevent kidney disease, they wrote in the Public Library of Science journal PLoS Genetics.