Kidney disease is a "hidden epidemic" affecting more than 850 million people worldwide, renal experts say.
That's twice the number of diabetics (422 million) and more than 20 times the number of people with cancer (42 million) or HIV/AIDS (36.7 million).
But most people don't realize that kidney disease is a major health issue.
"It is high time to put the global spread of kidney diseases into focus," said David Harris and Adeera Levin of the International Society of Nephrology. Harris is the group's president and Levin is past president.
They noted that kidney diseases often cause no early symptoms. And many people aren't aware of their increased risk for heart problems, infections, hospitalization and kidney failure.
Chronic kidney diseases (ones lasting more than three months) affect 10 percent of men and nearly 12 percent of women around the world. Up to 10.5 million people need dialysis or a kidney transplant, but many don't receive these lifesaving treatments due to cost or lack of resources.
In addition, more than 13 million people suffer acute kidney injury. Some will go on to develop chronic kidney disease or kidney failure.
"Using all these sources of data, and existing estimates of acute and chronic kidney diseases, we estimate approximately 850 million kidney patients -- a number which surely signifies an 'epidemic' worldwide," Levin said.
Kidneys remove waste products and help balance the volume of fluids and minerals in the body. They also produce a hormone that tells the body to make red blood cells, the researchers explained.
Even if many patients with damaged kidney function don't feel ill, they're at high risk for other health problems, said Carmine Zoccali, president of the European Renal Association -- European Dialysis and Transplant Association.
Heart disease deaths due to chronic kidney disease are high -- 1.2 million cardiovascular deaths were attributed to kidney disease in 2013.
"The number of people with kidney diseases is alarmingly high, but the public is not aware of this reality. These patients have outcomes and kidney diseases impose a heavy financial burden on health care budgets," said Mark Okusa, president of the American Society of Nephrology.
The annual per-patient cost of dialysis is $88,195 in the United States, he said in a ASN news release.