By Thomas H. Hostetter, MD

Dr. Hostetter raises awareness of the seriousness of kidney disease as well as the importance of its prevention, early diagnosis and appropriate management.

The earlier that kidney disease is detected, the more effective the treatment. Today people with early kidney disease in most cases can receive treatment that will delay or even prevent kidney failure. In addition, treatment can probably prevent many of the heart and vascular conditions, such as a stroke, that complicate kidney disease.

While diagnosis and treatment can be beneficial at any stage, the most benefit comes when the disease is identified early. The problem is that with early kidney disease there are usually no symptoms. When advancing kidney damage symptoms like fatigue, poor appetite or sleepiness become noticeable, some people have already lost more than half of their kidney function. Therefore, laboratory testing is the only way to know if kidney disease is present.

Most people who develop serious kidney disease — serious enough that it puts them at risk for progression to kidney failure or heart and vascular disease — have diabetes, hypertension (high blood pressure) or both. Therefore, these people should be checked regularly for kidney injury. Current guidelines call for yearly urine testing in people with diabetes. Experts have not yet determined the best frequency to test people with hypertension alone. A reasonable interval seems also to be yearly, but at least every two years.

In addition to those with diabetes or hypertension, first-degree relatives (children, siblings, parents) of people with kidney failure should also be tested. The guidelines for this group are still undecided, but it is clear that these relatives are at high risk for kidney disease. Thus, some testing is reasonable. They should also be assessed for diabetes and high blood pressure in addition to the laboratory tests of kidney function. The right interval for testing relatives has not been generally agreed upon. However, every three years seems an adequate period so long as they do not have diabetes or high blood pressure.

Although 75 percent of those developing kidney failure have diabetes, hypertension or both and early detection and treatment of these conditions is effective, the remaining 25 percent of people with kidney failure do not have these underlying risk factors. Currently, there is no useful screening or testing methods for most of these people. At this time, there are no efficient means of screening for early forms of most types of glomerulonephritis. Directly inherited diseases such as polycystic kidney disease or Alport’s syndrome can be detected relatively early, usually because the strong pattern of inheritance prompts investigation.

The two routine tests for kidney disease are measurement of albumin in the urine and measurement of creatinine in the blood. Albumin is a normal protein in the blood but it leaks into the urine when the kidneys are damaged. The easiest test for urine albumin is a dipstick test. The result is expressed as the amount of protein in the urine, or “proteinuria.” Often the result is reported as negative to 4+ with 4+ meaning the highest on this rough scale. However, this test is not sensitive enough for testing in diabetes and perhaps even for other forms of early kidney disease.

For diabetes, a urine specimen needs to have albumin measured specifically in the laboratory. The simplest method is to test a random or “spot” urine specimen and measure albumin and creatinine in it. The amount of albumin is expressed as a ratio to the creatinine. The albumin to creatinine ratio should be less than 30 milligrams (mg) albumin per one gram (g) of creatinine. Levels over 30 are abnormal. Because the test is sensitive, if it is abnormal, it should be confirmed with a second measurement a few weeks later. 24-hour collections to measure albumin or protein excretion are not needed. They are no more accurate than the more convenient “spot” sample. 

Who should be tested for chronic kidney disease?
• People with diabetes.
• People with hypertension.
• People with a relative with kidney failure.

What tests should be done?
• A spot urine test.

This test allows a physician to measure albumin and creatinine in the urine.
• A blood test.

This test allows a physician to measure the creatinine level in the blood. Creatinine can be used to estimate one’s glomerular filtration rate (GFR).

How often should testing occur?
• Once a year for people with diabetes.
• Every one to three years for individuals with high blood pressure and relatives of people with kidney failure.

The creatinine level in the blood (often expressed as serum or plasma level) indicates the filtration rate of the kidneys. The lower the filtration rate, the higher the blood creatinine level climbs. However, the exact relation between blood creatinine and the actual filtration rate is complicated. For this reason equations have been developed that allow fairly accurate estimation of the glomerular filtration rate (GFR) from the creatinine level if the patient’s age, sex and race are known. There are many Web sites, such as the National Kidney Disease Education Program’s, www.nkdep.nih.gov, that can do this calculation and certain clinical laboratories have begun to do it automatically. This approach of estimating the filtration rate from the creatinine level seems to be superior to the older and more cumbersome method of collecting a 24-hour urine specimen. The exact normal level depends somewhat on age, but values below 60 milliliter (ml) per minute are decidedly low.

Special tests may be needed for some cases. For example, polycystic kidney disease requires an image of the kidney with an ultrasound, CT scan or MRI. Some diseases, especially the different kinds of glomerulonephritis, may need a biopsy. However, most kidney disease can be detected very early with the simple blood and urine tests just described. The costs of the simple tests vary but are in the range of $20-$30 for each. Most insurers would probably pay for the tests in people with a risk for kidney disease.

In summary, people with diabetes or high blood pressure or a relative with kidney failure should get a urine and blood test to check for kidney disease. They should ask their doctor to do these tests regularly. Early kidney disease has no symptoms. Testing is the only way to find it and begin treatment.

Thomas H. Hostetter, MD, is a senior scientific adviser and director of the National Kidney Disease Education Program at the National Institute of Diabetes and Digestive and Kidney Diseases. Dr. Hostetter is also professor of medicine on leave from the University of Minnesota, where he was director of the renal division in the department of internal medicine for 15 years.

This article originally appeared in the March/April 2004 issue of Kidney Beginnings: The Magazine, Vol. 3, No. 1.

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