In the U.S., about 11 percent of adults have chronic kidney disease, the vast majority of whom have early-stage disease.

The disease is very common among older adults -- more than 44 percent of Americans older than 70 have it -- and high blood pressure and diabetes are the main risk factors.

In its early stages, chronic kidney disease usually has no symptoms. But there are blood and urine tests that can catch signs of trouble, so it may sound logical to use them to screen everyone for early kidney dysfunction.

The problem is, no clinical trials have tested the effectiveness of widespread screening, according to the new review published in the Annals of Internal Medicine.

Nor have there been clinical trials to see whether routine monitoring of people with early kidney disease improves their long-term outlook.

Controlled clinical trials -- in which people are randomly assigned to have a particular intervention or not -- are considered the "gold standard" of medical research.

"This doesn't mean (screening and monitoring) are not beneficial," said Dr. Howard Fink, a staff physician at the Veterans Affairs Medical Center in Minneapolis, who led the study. "The bottom line is that it's uncertain."

Fink and his colleagues conducted the review of existing research on this subject for the U.S. Preventive Services Task Force (USPSTF), a government-backed advisory group. The panel is currently revisiting its recommendations on kidney cancer screening; right now, there is no recommendation for or against it.

And that's "unlikely to change," given the lack of clinical trials, according to Drs. Katrin Uhlig and Andrew Levey of Tufts Medical Center in Boston, who wrote an editorial published with the review.

Before experts recommend widespread screening for a disease -- which, by definition, means testing symptom-free people -- they want evidence that the benefits outweigh the risks.

"On its surface, it seems like screening for a disease would be beneficial," Fink said in an interview.

But, he said, with any screening test, some people will get "false positive" results. And that will often lead to unnecessary (and possibly invasive) follow-up tests, extra costs and anxiety.

With chronic kidney disease, there have been no studies on the benefits or harms of widespread screening. "Right now, all the screening-related harms are theoretical," Fink said. And so, too, are the benefits.

It's also unclear whether it would be wise to routinely test all people with early-stage kidney disease to see if the problem is worsening over time.

Fink noted that only a small percentage of people with early disease will actually progress to end-stage kidney failure -- at which point dialysis or a kidney transplant are needed.

The review did, however, find evidence that certain kidney disease treatments can slow the progression of the disease.

Fink's team found 110 clinical trial reports on treatments. Overall, two types of blood pressure drugs -- ACE inhibitors and angiotensin II-receptor blockers (ARBs) -- lowered people's risk of developing end-stage kidney disease by about one-quarter to one-third.

But that benefit was largely limited, Fink said, to people with diabetes and high blood pressure, plus large amounts of protein in the urine (known as macroalbuminuria).

Based mainly on one trial, ACE inhibitors seemed to lower death risk in people with diabetes or cardiovascular disease.

According to Fink, if screening is going to work, the "best chance" would come from targeting it to those people who are at increased risk and most likely to benefit from early treatment.

Of course, many people with high blood pressure or diabetes will already be on an ACE inhibitor or ARB, Fink pointed out. So the added value of screening them for kidney disease is still not clear.

On top of that, those same patients will usually automatically have their glomerular filtration rate (GFR), an important measure of how well the kidneys are working, reported after routine blood work at their doctor's office, said Uhlig.

"This diminishes the benefit from screening," she told Reuters Health in an email.

For patients, the main thing is to get their risk factors for kidney disease under better control, according to Uhlig.

"Even without strong evidence on the benefits of screening for chronic kidney disease," she said, "risk factors like hypertension (high blood pressure) and diabetes require treatment to avoid kidney disease, as well as cardiovascular disease."

As for people who already have early-stage kidney disease, some type of monitoring is needed, according to Uhlig.

"However," she said, "how often and how depends on many factors: the type of disease, the speed with which the disease progresses, treatments, other healthcare problems."

SOURCE: bit.ly/HTd5UT and bit.ly/HQmU1p Annals of Internal Medicine, April 17, 2012.

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