Tests to Detect Kidney Disease

Medical Tests to Detect Kidney Disease

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Kidney disease may occur initially without any signs or symptoms. The doctor may first detect the condition through routine blood and urine tests. To detect kidney disease, the doctor may use the following tests and diagnostic procedures.

Blood Pressure Measurement

High blood pressure, like kidney disease, may not have early signs or symptoms. High blood pressure can lead to kidney disease. In addition, it may also be a sign that the kidneys are already impaired. Having blood pressure measured by a health professional is the only way to know whether it is high. The result is expressed as two numbers. For example, 120/80 (expressed as 120 over 80). The top number represents the pressure when the heart is beating. It is called the systolic pressure. The bottom number, which is called the diastolic pressure, represents the pressure when the heart is resting between beats. A blood pressure is considered normal when it stays below 120/80. The National Heart, Lung, and Blood Institute (NHLBI) recommends that people with kidney disease should keep their blood pressure below 130/80.

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Tests for Microalbuminuria and Proteinuria

Microalbuminuria is a condition where small amounts of albumin leak into the urine. This may be a sign that kidney function is slowly deteriorating. Normally, the kidneys work to take wastes out of the blood but leave protein. However, impaired kidneys may not be able to separate the blood protein called albumin from the wastes. Proteinuria occurs when large amounts of albumin and other proteins leak into the urine. The doctor may test for protein by using a dipstick in a small urine sample. The color of the dipstick indicates the presence or absence of proteins in the urine.

Another more sensitive test for proteins or albumin in the urine involves laboratory measurement and calculation of the protein-to-creatinine or albumin-to-creatinine ratio. Experts suggest that this test should be used to detect kidney disease in people at high risk, especially those with diabetes. If the first test reveals high levels of protein, another test should be done 1 to 2 weeks later. Persistent proteinuria is the term used when the second test also shows high levels of protein. Additional tests and procedures should be used to determine kidney function.

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Glomerular Filtration Rate Based on Creatinine Measurement

Glomerular filtration rate, or GFR, is a calculation of how the kidneys are efficiently filtering wastes from the blood. GFR calculation requires measurement of creatinine in a blood sample along with weight, age, and values assigned for sex and race.

Creatinine is a waste product that results from the normal breakdown of muscle cells during activity. The kidneys normally take this waste out of the blood and put in the urine. However, when the kidneys are not working properly, creatinine builds up in the blood.

A GFR calculation is more accurate for determining whether a person has impaired kidney function.

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Blood Urea Nitrogen (BUN)

Urea, a compound that contains nitrogen, is a waste product that results after the cells have used protein. Normally, the kidneys take urea out of the blood and put it in the urine. Urea will build up in the blood when the kidneys are not working well.

A deciliter of normal blood contains 7 to 20 milligrams of urea. A BUN more than 20 mg/dL might indicate that kidney function is impaired. Dehydration and heart failure may also cause BUN to become elevated.

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Additional Tests for Kidney Disease

Additional tests may be required to help the doctor identify the cause of problem if blood and urine tests indicate reduced kidney function.

Kidney Imaging. The doctor will use kidney imaging, also known as renal imaging, to take pictures of the kidneys. It includes ultrasound, magnetic resonance imaging (MRI), and computed tomography (CT) scan. These imaging tools are helpful in finding unusual growth or blockages to urine flow.

Kidney biopsy. Also called renal biopsy, kidney biopsy is a procedure that requires a sample of kidney tissue that is studied under a microscope. The doctor gets the kidney tissue sample by inserting a needle through the person’s skin into the back of the kidney. The patient may be fully awake with light sedation, or may be asleep under general anesthesia. This kidney test helps the doctor to identify problems at the cellular level.

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National Kidney and Urologic Diseases Information Clearinghouse. Your Kidneys and How They Work. National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD. NIH Publication No. 07-3195. Available at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/index.htm. Accessed July 2008

National Kidney and Urologic Diseases Information Clearinghouse. Kidney Biopsy. National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD. NIH Publication No. 05–4763, January 2005. Available at http://kidney.niddk.nih.gov/kudiseases/pubs/biopsy/index.htm. Accessed July 2008

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