Diseases that affect the kidney can be difficult for a patient or doctor to diagnose without using a variety of diagnostic tests. Kidney function tests are defined by the Encyclopedia of Surgery as a variety of procedures that evaluate whether a patient's kidneys are performing properly. These diagnostic tests for kidney function can also help doctor's determine the best treatment to combat the specific disease.
Urinalysis
The chief role of the kidneys is to filter out ammonia and wastes from the body. The kidney does this by producing urine. If the kidney is failing, the urine it produces is abnormal and can be measured. The test to measure the urine is called a urinalysis. The Department for Works and Pensions, a UK government agency, lists urinalysis as the most important test for verifying kidney damage. A urinalysis looks at the color of the urine and the presence of protein, glucose, blood and ketones. The presence of any of these substances in the urine can point to damage to the kidney.
Urine is also examined microscopically for white blood cells, which indicate infection, red blood cells, which indicate kidney damage, small bodies called casts and bacteria. Any of these products in the urine point to kidney damage.
Urine Tests
There are specific tests that can be done to further evaluate kidney function. These tests have been enumerated by the Encyclopedia of Surgery.
Creatinine clearance is a test that requires a 24-hour urine collection. The test measures the levels of creatinine in the urine. Creatinine is a product of the body that is always standard within the urine. A change in the normal concentration of creatinine in the urine is an indication of kidney disease.
Urine osmolality measures the amount and concentration of waste products in the urine. Normal values have been established by years of clinical experience and any variation from the normal indicates that the kidneys may not be filtering the blood properly.
Urine protein is measured using a 24-hour urine collection. Normal values are less than 150mg of protein. Higher levels mean that the kidney is damaged and is allowing proteins to exit from the blood.
Blood Pressure Measurement
A consistently high blood pressure can be a sign that the kidneys have been damaged, according to National Kidney and Urologic Disease Information Clearinghouse (NKUDIC). Any pressure that is above normal can be a sign that the kidneys are overproducing a hormone, renin, which causes blood pressure to increase. Kidney damage can cause the kidneys to overproduce renin.
Glomerular Filtration Rate (GFR)
Glomerular filtration rate, according to NKUDIC, is a calculation of how efficiently the kidneys are filtering wastes from the body. Patients with early-stage kidney disease will only have slightly elevated levels of GFR and may not experience any symptoms, but the high levels mean that the kidneys are damaged.
Blood Urea Nitrogen (BUN)
The blood brings urea, a nitrogen containing waste product, to the kidneys for excretion. If the kidneys are not functioning properly, the urea remains trapped in the blood. A test for blood urea nitrogen is listed by the NKUDIC as an important test for measuring kidney function.
Kidney Imaging Tests
There are many tests that can help doctors visualize the kidneys. These imaging tests are listed by the Department for Work and Pensions. They include abdominal X-rays which can spot kidney stones, kidney ultrasound, a common test that can show the size and structure of the kidney and the presence of any abnormal masses, computer tomography (CT) scanning which is used to visualize the soft tissues of the kidney, and magnetic resonance imaging (MRI) scanning that provides a three-dimensional view of the kidney.
Intravenous pyelography (IVP) is an imaging test that uses iodine as a dye that can be seen on X-ray. As the iodine is excreted by the kidneys, the dye can be used to visualize almost all the structures of the urinary system. The main benefit of the test is showing the collecting system of the kidneys, the presence of stones and any malignancy.
Kidney Tissue Biopsy
There are times when a doctor may need a microscopic part of kidney tissue in order to diagnose kidney disease. The NKUDIC states that a kidney tissue biopsy can be used by doctors to directly visualize the microscopic layers of the kidney. Biopsies can tell if there is any minute damage to the kidney or if a certain treatment for kidney disease is working.
