They can be damaged by drugs and disease. The vast majority of people with kidney disease don't know it. That's because it damages the organs slowly over many years before causing symptoms. And left untreated, the condition can eventually require people to spend hours hooked up to a dialysis machine or get a kidney transplant. Even mild kidney problems can contribute to anemia, bone loss, worsened heart disease, and premature death.

All that is particularly worrisome now because several factors have conspired to make kidney disease more common than ever. One is the increasing number of people who take multiple medications, which travel through the kidney as they leave the body, taxing the organ. Another is the growing, and related, epidemic of type 2 diabetes and high blood pressure, both of which further strain the kidneys. People over age 60 are especially vulnerable both because they tend to take more drugs, and because kidney function normally declines somewhat with age.

Protecting the Body's Filters

Fortunately, there are several steps people can take to ward off or rein in kidney damage. And they might be able to spot some early warning signs of kidney problems by watching for changes in urinary habits or urine's appearance. More important, improved—but underused—tests can now help diagnose the problem early, when it's most treatable.

Blood passes through a labyrinth of tiny filters in the kidneys that separate substances that the body needs, such as calcium, sodium, and water, from wastes created by the breakdown of food and drugs. The kidneys maintain a balance of the useful substances and eliminate the waste and excess fluid as urine.

Diabetes and high blood pressure can overload the kidneys' precision workings, causing irreversible scarring and shrinkage. So one key to preventing kidney damage is making the lifestyle changes—notably consuming a healthy diet and exercising regularly—that combat both health problems. Drugs to lower high blood pressure or control diabetes are also often necessary. It's especially important that people with diabetes take ACE inhibitors such as lisinopril (Prinivil, Zestril, and generic) or ARBs such as candesartan (Atacand), which offer strong kidney protection.

But many other medications, especially when used excessively or in high dosages, can harm the kidneys. The biggest concerns are probably ibuprofen (Advil and generic), naproxen (Aleve and generic), and related nonsteroidal anti-inflammatory drugs. And cholesterol-lowering statin drugs such as atorvastatin (Lipitor) and lovastatin (Mevacor and generic) can, in rare cases, harm the muscles, releasing a protein that can seriously damage the kidneys. People should make sure they take all medications according to directions, and periodically review all drugs and supplements with their doctor.

And since research suggests that kidney stones may also damage the organs, it makes sense to prevent the painful crystals from forming in the first place. The most effective step is drinking plenty of liquids. But people might want to go easy on colas: Some evidence suggests their high levels of phosphoric acid may damage the kidneys, possibly by fostering the growth of stones.

Early Detection is Critical

People with declining kidney function typically experience no symptoms until failure is imminent. And until recently doctors had no good way to detect early signs of kidney failure. The most accurate measure required 24-hour urine collection. Simpler tests were so insensitive that by the time they showed abnormalities, the kidneys had often already lost more than half their filtering capacity.

But now researchers have validated a faster, easier way to detect kidney trouble: a blood test that is factored into a formula that also uses age, gender, and race to estimate the kidney's filtration rate, combined with a test to measure excreted protein. Testing is especially important if people are age 60 or over; have a personal history of diabetes, heart disease, high blood pressure, or any kidney disease; or have a family history of kidney disease.

An abnormal result, especially on the protein test, does not necessarily mean that someone has kidney damage, since a bladder infection or other problems can increase protein excretion. If people have an abnormal result, they should get retested in a few months. A second abnormal finding indicates the need for further investigation.

Stopping the Damage

If a person is diagnosed with kidney disease, there are certain key steps to take to help contain the damage. "It's not a hopeless diagnosis," says David Ellison, M.D., a kidney specialist and professor at Oregon Health and Science University and the Portland Veterans Affairs Medical Center.

Lifestyle changes that help prevent the disease can also slow it down. And certain steps become especially important:

* Aggressively control high blood pressure and diabetes. For blood pressure, that means lower-than-normal targets. Getting systolic level under 130 millimeters of mercury and diastolic under 80 mm/Hg, with drugs if necessary. ACE inhibitors and ARBs are especially good choices because of their proven ability to protect the kidneys.

* For diabetes, research shows that every percentage-point drop in the A1C blood test—a measure of blood-sugar control—can cut the risk of kidney disease and other complications by up to about 40 percent. The American Diabetes Association recommends an A1C target of 7 percent, but people should ask their doctor about the pros and cons of aiming even lower.

* Cut back on sodium and possibly potassium. Kidney damage impairs excretion of those electrolytes, and reducing sodium intake can help lower blood pressure.

* Lose excess weight. In one recent study, overweight people who had kidney disease suffered organ failure two to five times faster than individuals with a normal weight.

* Limit protein in the diet. Too much can overtax diseased kidneys. So talk with a nutritionist about how to cut back on the amount in the daily diet.

This article first appeared in the April 2008 issue of Consumer Reports on Health.