Your kidneys play a key role in keeping your blood pressure under control. Blood pressure, in turn, can damage your kidneys. High blood pressure, also called hypertension, can damage the kidneys.
Hypertension can result from too much fluid in normal blood vessels or from normal fluid in narrow blood vessels. Blood pressure that remains high over time is called hypertension. Extra salt and fluid in your body increases the amount of fluid in your blood vessels and makes your blood pressure higher. Narrow or clogged blood vessels also raise your blood pressure. If you have high blood pressure, see your doctor regularly.
High blood pressure makes your heart work harder and, over time, can damage blood vessels throughout your body. If the blood vessels in your kidneys are damaged, kidneys may stop removing wastes and extra fluid from your body. The extra fluid in your blood vessels may then raise blood pressure even more. It's a dangerous cycle.
High blood pressure is one of the leading causes of kidney failure, also commonly called end-stage renal disease (ESRD). People with kidney failure must either receive a kidney transplant or go on dialysis. Every year, high blood pressure causes more than 25,000 new cases of kidney failure in the United States.
Most people with high blood pressure have no symptoms. The only way to know whether your blood pressure is high is to have a health professional measure it with a blood pressure cuff. The result is expressed as two numbers. The top number, which is called the systolic pressure, represents the pressure when your heart is beating. The bottom number, which is called the diastolic pressure, shows the pressure when your heart is resting between beats. Your blood pressure is considered normal if it stays below 120/80 (expressed as "120 over 80"). People with a systolic blood pressure of 120 to 139 or a diastolic blood pressure of 80 to 89 are considered pre-hypertensive and should adopt health-promoting lifestyle changes to prevent diseases of the heart and blood vessels. If your systolic blood pressure is consistently 140 or higher or your diastolic pressure is 90 or higher, you have high blood pressure and should talk with your doctor about the best ways to lower it.
Kidney damage, like hypertension, can be unnoticeable and detected only through medical tests. Blood tests will show whether your kidneys are removing wastes efficiently. The test to look at your kidney function is your serum creatinine. Having too much creatinine in your blood is a sign that you have kidney damage. The doctor should use the serum creatinine to estimate the main kidney function called glomerular filtration rate, or GFR.
Another sign is proteinuria, or protein in your urine. Proteinuria has also been shown to be associated with heart disease and damaged blood vessels.
If you have kidney damage, you should keep your blood pressure below 130/80. The National Heart, Lung, and Blood Institute (NHLBI), one of the National Institutes of Health (NIH), recommends that people with kidney disease use whatever therapy is necessary, including lifestyle changes and medicines, to keep their blood pressure below 130/80.
NHLBI has found that six lifestyle changes can help control blood pressure:
- Maintain your weight at a level close to normal. Choose fruits, vegetables, grains, and low-fat dairy foods.
- Limit your daily sodium (salt) intake to 2,000 milligrams or lower if you already have high blood pressure. Read nutrition labels on packaged foods to learn how much sodium is in one serving. Keep a sodium diary.
- Get plenty of exercise, which means at least 30 minutes of moderate activity, such as walking, most days of the week.
- Avoid consuming too much alcohol. Men should limit consumption to two drinks (two 12-ounce servings of beer or two 5-ounce servings of wine or two 1.5-ounce servings of "hard” liquor) a day. Women should have no more than a single serving on a given day because metabolic differences make women more susceptible to the effects of alcohol.
- Limit caffeine intake.
- Quit cigarette smoking.
Many people need medicine to control high blood pressure. Two groups of medications called ACE (angiotensin-converting enzyme) inhibitors and ARBs (angiotensin receptor blockers) lower blood pressure and have an added protective effect on the kidney in people with diabetes. Additional studies have shown that ACE inhibitors and ARBs also reduce proteinuria and slow the progression of kidney damage in people who do not have diabetes. You may need to take a combination of two or more blood pressure medicines to stay below 130/80. Your doctor may also prescribe a diuretic in addition to your ACE inhibitor or ARB. Diuretics are also called "water pills" because they help you urinate salt and water from your body.
All racial groups have some risk of developing kidney failure from high blood pressure. African Americans, however, are more likely than Caucasians to have high blood pressure and to develop kidney problems from it – even when their blood pressure is only mildly elevated. In fact, African Americans are about six times more likely than Caucasians to develop hypertension-related kidney failure.
People with diabetes also have a substantially increased risk for developing kidney failure. People who are at risk both because of their race and because of diabetes should have early management of high blood pressure.
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), also part of NIH, sponsored the African American Study of Kidney Disease and Hypertension (AASK) to find effective ways to prevent high blood pressure and kidney failure in this population. The results, released in 2003, showed that an ACE inhibitor was better at slowing the progression of kidney disease in African Americans than either of two other drugs.