The routine blood and urine tests listed below may provide the first indication of a kidney problem or may be ordered if chronic kidney disease (CKD) is suspected due to a person's signs and symptoms. These tests reflect how well the kidneys are removing excess fluids and wastes and some are included in the basic and comprehensive metabolic panels (BMP and CMP).
A blood pressure measurement is also important since high blood pressure (hypertension) can lead to CKD. When a structural problem is suspected, a variety of imaging tests can be used to evaluate the kidneys. A sample of kidney tissue, a biopsy, is sometimes helpful in diagnosing the specific cause of a problem.
Tests commonly used for screening and diagnosis
The National Kidney Foundation (NKF) and the National Kidney Disease Education Program (NKEDP) recommend that people who are at high risk be screened for kidney disease to detect it in its earliest stages. Risk factors include diabetes, high blood pressure, heart disease, or a family history of these or kidney disease. The NKF recommends that everyone with diabetes between the ages of 12 and 70 be screened for kidney disease at least once a year. At this time, there is no consensus on screening people who have no risk factors or symptoms. The NKF and NKDEP recommend two tests, in addition to blood pressure measurement, to screen for kidney disease:
- Urine protein—a few different tests may be used to screen for protein in the urine:
- Urine albumin—this test may be done on a 24-hour urine sample, or both urine albumin and creatinine can be measured in a random urine sample and the albumin/creatinine ratio (ACR) can be calculated. The American Diabetes Association recommends ACR as the preferred test for screening for albumin in the urine (microalbuminuria).
- Urinalysis—this is a routine test that can detect protein in the urine as well as red blood cells and white blood cells. These are not normally found in the urine and, if present, may indicate kidney disease.
- Urine total protein or urine protein to creatinine ratio (UP/CR)—detects not just albumin, but all types of proteins that may be present in the urine.
While urinalysis and urine total protein are not as sensitive as urine albumin for detecting kidney damage, these tests give fewer false signals of kidney damage.
- Estimated glomerular filtration rate (eGFR)—a blood creatinine test or possibly a cystatin C test is performed in order to calculate the eGFR. The glomerular filtration rate refers to the amount of blood that is filtered by the glomeruli per minute. As a person's kidney function declines due to damage or disease, the filtration rate decreases and waste products begin to accumulate in the blood.
Some additional tests that may be ordered to evaluate for kidney disease include:
- Urea (urea nitrogen or BUN)—the level of this waste product in the blood increases as kidney filtration declines. Increased BUN levels suggest impaired kidney function, although they can also be elevated due to a condition that results in decreased blood flow to the kidneys, such as congestive hear failure, heart attack, or shock.
- Creatinine clearance—this test measures creatinine levels in both a sample of blood and a sample of urine from a 24-hour urine collection. The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into the urine. This calculation allows for a general evaluation of the amount of blood that is being filtered by the kidneys in a 24-hour time period.
Tests to monitor kidney function
If a person has been diagnosed with a kidney disease, several laboratory tests may be ordered to help monitor kidney function. Some of these include:
- Blood levels of BUN and creatinine are measured from time to time to see if the kidney disease is getting worse.
- The amount of calcium and phosphorus in the blood, blood gases (ABGs), and the balance of serum and urine electrolytes can also be measured as these are often affected by kidney disease.
- Hemoglobin in the blood, measured as part of a complete blood count (CBC), may also be evaluated as the kidneys make a hormone, erythropoietin, that controls red blood cell production and this may be affected by kidney damage.
- Erythropoietin may be measured directly, although this is not a routine test.
- Parathyroid hormone (PTH), which controls calcium levels, is often increased in kidney disease and may be checked to help determine if enough calcium and vitamin D are being taken to prevent bone damage.
- Cystatin C is another test that may sometimes be used as an alternative to creatinine to screen for and monitor kidney dysfunction in those with known or suspected kidney diseases.
- Both blood and urine beta 2 microglobulin (B2M) tests may be ordered along with other kidney function tests to evaluate kidney damage and disease and to distinguish between disorders that affect the glomeruli and the renal tubules. Normally, only small amounts of B2M are present in the urine, but when the renal tubules become damaged or diseased, B2M concentrations increase due to the decreased ability to reabsorb this protein. When the glomeruli in the kidneys are damaged, they are unable to filter out B2M, so the level in the blood rises. B2M tests may sometimes be ordered to monitor people who have had a kidney transplant, to detect early signs of rejection, and ordered to monitor people who are exposed to high levels of cadmium and mercury, such as with occupational exposure.
Tests to help determine the cause and/or guide treatment
Other tests may be ordered to help determine the cause and/or guide treatment, depending on several factors including a person's signs and symptoms, physical examination, and medical history. Some examples of these tests include:
- Urinalysis with a urine culture may be done when someone has symptoms suggesting infection to confirm the presence of a bacterial infection.
- Hepatitis B or C testing—to detect a hepatitis viral infection associated with some types of kidney disease
- Antinuclear antibody (ANA)—to help identify an autoimmune condition such as lupus that may be affecting the kidneys.
- Kidney stone risk panel—this test evaluates a person's risk of developing a kidney stone, to help guide and monitor treatment and prevention
- Kidney stone analysis—this test determines the composition of a kidney stone passed or removed from the urinary tract and may be done to help determine the cause of its formation, to guide treatment, and prevent recurrence
- Complement tests, most commonly C3 and C4—may be tested and monitored with glomerulonephritis
- Urine protein electrophoresis—may be done to determine the source of a high level of protein in the urine
- Myoglobin—in people who have had extensive damage to their skeletal muscles (rhabdomyolysis), a urine myoglobin test may be ordered to determine the risk of kidney damage. With severe muscle injury, blood and urine levels of myoglobin can rise very quickly.
If a structural problem or blockage is suspected, imaging of the kidneys can be helpful. Imaging techniques such as an ultrasound, CT scan (computed tomography), isotope scan, or intravenous pyelogram (IVP) may be used. For more on these see RadiologyInfo's web pages on Kidney and Bladder Stones or Kidney (Renal) Failure.
A biopsy is sometimes used to help determine the nature and extent of structural damage to a kidney. Analyzing a small piece of kidney tissue, obtained using a biopsy needle and diagnostic imaging equipment, can sometimes be useful when disease of the glomeruli (or sometimes the tubules) is suspected.
Tests for biomarkers of acute kidney injury
Several biomarkers are gaining attention as early indicators of acute kidney injury (AKI). Studies suggest that blood or urine tests for these biomarkers can detect acute kidney damage earlier than currently used kidney function tests, such as serum creatinine. Early detection of AKI is critical because injury occurs rapidly over a period of hours to days. AKI biomarkers are still being studied and may become more widely available in the future.
Although AKI is a serious condition and costs the U.S. healthcare system millions of dollars each year, the measurement of AKI biomarkers does not directly help in treating people with AKI because there are no FDA-approved therapies currently available. When AKI is diagnosed, imaging scans of the kidneys are frequently performed to rule out the presence of an obstruction in the urinary tract. General supportive treatment may be given, such as IV fluids or transfusion of blood components. Drugs used to improve blood pressure and heart function may be used if a person is in shock. If a person does not recover from AKI spontaneously, some type of dialysis is required.
Examples of promising AKI biomarkers include:
- Urinary insulin-like growth factor-binding protein 7 (IGFBP7) and urinary tissue inhibitor of metalloproteinases-2 (TIMP-2)—these two markers have been combined into a point-of-care test. It is the first test approved by the U.S. Food and Drug Administration to help assess critically ill patients for risk of developing AKI within the next 12 hours.
- Neutrophil gelatinase-associated lipocalin (NGAL)—this is a protein that is found in many tissues in the body, including kidney cells. Part of the reason NGAL is a good indicator of AKI is that its level rises rapidly in response to kidney injury, typically within 2-4 hours (read NGAL Shows Promise as Early Marker of Acute Kidney Injury).