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Various blood tests can be performed to determine if kidney disease is present, how severe it may be, and what may be causing it. In addition, a urinalysis and imaging techniques may also help to determine the cause and severity.
Chemistry panel
Different types of tests are performed to help diagnose the disease process. Multiple tests can be performed on one blood sample. Tests that are often included in a chemistry panel being run to look for kidney disease include:
Blood urea nitrogen (Serum urea nitrogen): BUN is the abbreviation for blood urea nitrogen. The proteins that animals consume in their diet are large molecules. As they are broken down and used by the body, the by-product is a nitrogen-containing urea compound. This is of no use to the body and is excreted by the kidneys. If the kidneys are not working correctly and filtering these waste-products, they build up in the blood. A twelve-hour fast (no food intake) is ideal before taking this test as the level may rise slightly after eating protein.
Creatinine: Creatinine is also used to measure the filtration rate of the kidneys. The kidneys are the only organs that excrete this substance, and if it builds up to higher than normal levels, it is a sign of decreased or impaired function of the kidneys.
Azotemia is the medical term for an increase in the BUN or creatinine. Uremia is defined as azotemia plus clinical signs of renal failure such as anemia, polyuria-polydipsia, vomiting, or weight loss. Azotemia is divided further into prerenal, renal, or postrenal causes. Prerenal azotemia is due to causes other than actual kidney malfunction that decrease the blood flow to the kidney. These include dehydration, Addison's disease, or heart disease. Renal azotemia occurs due to damage to the kidney itself, and can include chronic or acute renal disease/failure that results in more than 75% of the nephrons not functioning. Postrenal azotemia occurs when there is a build-up of pressure in the urinary system. Causes may include blockage of the urethra due to feline lower urinary tract disease (FLUTD) or bladder stones, which prevent urine from being removed from the body.
Phosphorus: Normal calcium and phosphorus levels in the blood are maintained by an interaction of three hormones on three body organs. The phosphorus level increases in kidney disease because less is excreted into the urine by the kidney. In cats, the phosphorus level may also increase due to hyperthyroid disease.
Dipstick test kit - UrinalysisUrinalysis
Multiple tests are performed on a urine sample. Several of them are especially important in determining if kidney disease is present.
Urine specific gravity: This test is a measurement of how concentrated the urine is. With kidney disease, the urine is not concentrated normally, and too much water is lost. A normal specific gravity is usually above 1.025, while animals with kidney disease may be in the 1.008 - 1.015 range. A low specific gravity should be retested to make sure it is a repeatable finding. Other diseases can cause a low specific gravity, so this test in itself, is not sufficient to make a diagnosis of kidney disease.
Protein: In some types of kidney disease, large amounts of protein are lost in the urine.
Sediment: The urine can be centrifuged so the larger particles may be separated out and examined under the microscope. The presence of red blood cells or white blood cells in the urine sediment help point to the cause of the disease condition. Casts (sloughed cells) from the kidneys may pass out in the urine. These indicate a disease process in the kidney itself.
ERD Screen Test: A blood test, called the ERD, tests for the presence of a certain protein in the urine called albumin. If the level is above normal, it is a very early indication of renal insufficiency and may be present before other signs of kidney disease appear. Identifying early renal disease allows for early treatment to begin to try to slow the disease process.
Complete Blood Count
A complete blood count (CBC) is useful to check for anemia and indications of infection. Anemia in renal failure is common and results from a decrease in the production of a erythropoietin by the diseased kidney. Erythropoietin is a hormone that tells the body to produce more red cells. The red blood cells also have a shorter life span in uremic patients.
Imaging techniques
Radiography: X-rays are taken to determine the size and shape of the kidneys. Small kidneys are more common in chronic kidney disease while large kidneys may indicate an acute problem or cancer.
Excretory urography such as an intravenous pyelography (IVP) is a specialized type of x-ray. A dye (positive contrast media) is injected into the pet's vein and monitored via x-rays as it is filtered out by the kidneys. This is used for anatomic evaluation of the urinary tract and to determine the size, shape, and location of the kidneys. It gives a crude assessment of renal function also.
Ultrasonography: Ultrasonography looks for changes in the density of the kidney. A biopsy taken during ultrasonography may help determine the cause of kidney disease in some cases.
Summary
By using the medical history, signs, physical examination and various other types of diagnostic tools, the veterinarian is better able to correctly diagnose a kidney disorder. By performing various tests, the list can be narrowed hopefully to one disease process. Then a treatment plan and prognosis can be provided.
