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Your Kidneys and How They Work

How Do Kidneys Fail?

Many factors that influence the speed of kidney failure are not completely understood. Researchers are still studying how protein in the diet and cholesterol levels in the blood affect kidney function.

Acute Renal Failure

Some kidney problems happen quickly, like an accident that injures the kidneys. Losing a lot of blood can cause sudden kidney failure. Some drugs or poisons can make your kidneys stop working. These sudden drops in kidney function are called acute renal failure (ARF).

ARF may lead to permanent loss of kidney function. But if your kidneys are not seriously damaged, acute renal failure may be reversed.

Chronic Renal Failure

Most kidney problems, however, happen slowly. You may have "silent" kidney disease for years. Gradual loss of kidney function is called chronic renal failure or chronic renal disease.

End-Stage Renal Disease

The condition of total or nearly total and permanent kidney failure is called end-stage renal disease (ESRD). People with ESRD must undergo dialysis or transplantation to stay alive.

What Are the Signs of Kidney Disease?

People in the early stages of kidney disease may not feel sick at all. The first signs that you are sick may be general: frequent headaches or feeling tired or itchy all over your body.

If your kidney disease gets worse, you may need to urinate more often or less often. You may lose your appetite or experience nausea and vomiting. Your hands or feet may swell or feel numb. You may get drowsy or have trouble concentrating. Your skin may darken. You may have muscle cramps.

How Will My Doctor Detect Kidney Disease?

First, your doctor will probably send blood and urine samples to a lab to test for substances that should not be there. If the blood contains too much creatinine or urea nitrogen and the urine contains protein, your kidneys may not be functioning properly.

Creatinine

Creatinine is a waste product in the blood created by the normal breakdown of muscle during activity. Healthy kidneys take creatinine out of the blood and put it in the urine to leave the body. When kidneys are not working well, creatinine builds up in the blood.

In the lab, your blood will be tested to see how many milligrams of creatinine are in one deciliter of blood (mg/dl). Creatinine levels in the blood can vary, and each laboratory has its own normal range. In many labs, the normal creatinine range is 0.6 to 1.2 mg/dl. If your creatinine level is only slightly above this normal range, you probably will not feel sick, but the elevation is a sign that your kidneys are not working at full strength. One formula for estimating kidney function equates a creatinine level of 2.0 mg/dl to 50 percent of normal kidney function and 4.0 mg/dl to 25 percent. But, because creatinine values are so variable and can be affected by diet, you may need to have your creatinine measured regularly to see whether your kidney function is decreasing.

WebMD Public Information from the U.S. National Institutes of Health

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