Chronic Kidney Disease - Exams and Tests

Exams and Tests

People who have chronic kidney disease may not have symptoms of the disease until kidney function has decreased to a very low level. Tests are vital to help determine:

• Whether kidney disease has developed suddenly or as a long-term process (acute renal failure versus chronic kidney disease). Some of the tests used to evaluate acute renal failure may also be used if a person with chronic kidney disease has a sudden drop in kidney function.
• What is causing the kidney damage.
• The best type of treatment to help slow the progression of kidney damage.
• How well treatment is working.
• When to begin dialysis or have a kidney transplant.

After you are diagnosed with chronic kidney disease, blood and urine tests can help monitor the disease.

Tests to check kidney function

When kidney function is decreased, substances such as urea, creatinine, and certain electrolytes begin to build up in the bloodstream. The following blood and urine tests measure changing levels of these substances in the bloodstream and can help estimate how well your kidneys are working.

• A fasting blood glucose test is done to measure your blood sugar. High blood sugar levels damage blood vessels in the kidneys.
• A blood test measures your levels of electrolytes, which are filtered out of the body by the kidneys. Altered levels of electrolytes, such as sodium and potassium, may mean the kidneys are not functioning adequately.
• A blood test for parathyroid hormone (PTH) checks the level of PTH in the blood. PTH helps control calcium and phosphorus levels in the blood. A high parathyroid hormone level can be caused by conditions that lead to low blood calcium levels, such as chronic kidney disease.
• Urine tests, such as urinalysis (UA) and random urine test for microalbumin, measure the amount of protein in the urine. Normally there is little or no protein in urine. Kidney disease can cause increased protein in the urine.

Kidney disease runs in families, so encourage close family members to have their kidney function tested. If kidney disease is found early, treatment can be started to slow or stop the damage.

Tests for anemia

If the kidneys do not produce enough of the protein erythropoietin needed to make red blood cells, anemia can develop. This type of anemia is treated with a medicine called human recombinant erythropoietin (rhEPO) that helps your body make new red blood cells.

Tests to monitor anemia include:

• Complete blood count (CBC). A CBC measures the hematocrit and the hemoglobin level, which shows how well dialysis or rhEPO therapy is working.
• Reticulocyte count. A low reticulocyte count often means decreased production of red blood cells by the bone marrow. Iron deficiency or low levels of erythropoietin can cause decreased production of red blood cells by the bone marrow.
• Iron studies. Your body needs iron for the proper function of hemoglobin, the protein in red blood cells that carries oxygen. Decreased production of red blood cells or the inability to store iron in the body can cause a low iron level.
  • Serum ferritin test, to measure the protein that binds to iron in the body. Decreased production of red blood cells, low iron in the body, or the inability to store iron in the body can cause a low level of serum ferritin.

Other tests

Your doctor may use other tests to monitor reduced kidney function or to determine whether another kidney disease or condition is contributing to reduced kidney function.

• An ultrasound of the kidney (renal ultrasound) accurately measures the size of the kidneys, which may help estimate how long chronic kidney disease has been present and to check whether urine flow from the kidneys is blocked. An ultrasound also may help identify other possible causes of kidney disease, such as obstruction or polycystic kidney disease.
• A duplex Doppler study or angiogram of the kidney may be done to check for problems caused by restricted blood flow (renal artery stenosis).
• A kidney biopsy may help determine the cause of chronic kidney disease. It may also be used after kidney transplant when organ rejection is suspected.

The dye used during CT scan and intravenous pyelogram (IVP) may damage the kidneys further, so these tests typically are not used to evaluate kidney disease.

Early screening for chronic kidney disease

Experts recommend screening tests for chronic kidney disease in high-risk groups, such as people with diabetes or high blood pressure. Being diagnosed with kidney disease before it has progressed gives you the best chance to control the disease.

Screening tests for people who have diabetes

Kidney damage caused by diabetes is called diabetic nephropathy. Doctors diagnose diabetic nephropathy with a urine test for microalbumin that detects protein in the urine. Normally there is little or no protein in urine. Kidney disease can cause increased protein in the urine, or proteinuria. The results of two tests done within a 3- to 6-month period are needed to diagnose diabetic nephropathy.

When to begin testing for protein in the urine depends on the type of diabetes you have. After testing begins, you should have it every year.

• Type 1 diabetes: Because it takes a few years before people with type 1 diabetes start showing signs of kidney damage, testing for protein in the urine is often done yearly after you have had the disease for 5 years. For children, testing usually begins at the time of puberty and continues yearly throughout life.
• Type 2 diabetes: Because people with type 2 diabetes have usually had the disease for several years before it is diagnosed, diabetes may have already caused some kidney damage. Testing for protein in the urine is often done yearly after type 2 diabetes is diagnosed.

For more information, see the topic Diabetic Nephropathy.

Screening tests for people who have high blood pressure

When you are first diagnosed with high blood pressure, you should have an estimate of glomular filtration rate (GFR) to check your kidney function. If your kidney function is normal and your blood pressure is normal with treatment, you will need to see your doctor yearly to have your overall health and kidney function evaluated.

Experts recommend that people with kidney disease keep their blood pressure below 130/80.³

During your yearly visit, your doctor may order a chemistry screen, which includes a urine test to measure the amount of protein in the urine. If your test results are normal and your blood pressure is under control, no further testing is needed. If initial tests are abnormal, more tests may be needed to evaluate your kidney function.

For more information, see the topic High Blood Pressure (Hypertension).