Tests performed on samples of your blood and urine are the first line of defense in detecting kidney problems and minimizing damage. Tests of these types can show how well the kidneys are removing excess fluids and waste. In addition, your blood pressure should be measured since high blood pressure (hypertension) can lead to kidney disease. When a structural problem is suspected, a variety of imaging tests can be used to evaluate the kidney. A sample of kidney tissue, a biopsy, is sometimes helpful in diagnosing the specific cause of the problem.
Tests commonly used for screening and diagnosis
There are several tests commonly used to help your health care provider recognize if you have kidney or urinary disease. A blood sample can be analyzed for creatinine (and the estimated glomerular filtration rate (eGFR) can be calculated) and blood urea nitrogen (BUN). The level of these waste products in the blood increases as kidney filtration declines. Abnormal results are usually the first sign that kidney disease is present. A urine sample is typically also examined and analyzed (urinalysis) as part of routine screening. This set of tests looks for indicators of kidney and urinary disease such as red blood cells, white blood cells (WBCs or leukocytes), and protein in the urine. If you have diabetes or hypertension, the amount of protein (microalbumin) in your urine should be checked at least yearly to detect kidney disease in its early stages. When a creatinine measurement is performed along with a random microalbumin, the result is the microalbumin/creatinine ratio (also called the albumin/creatinine ratio (ACR)), which the American Diabetes Association states is the preferred test for screening for microalbuminuria. When you have symptoms suggesting infection, a urine culture can confirm the presence of a bacterial infection.
Tests to monitor kidney function
If you have been diagnosed with a kidney disease, your health care provider will order laboratory tests to help monitor kidney function. 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 and the balance of serum and urine electrolytes can also be measured, as these are often affected by kidney disease. Hemoglobin, measured as part of a complete blood count (CBC) may be measured (the kidneys make a hormone, erythropoietin, that controls red blood cell production). Urine total protein (TP) can be used to test the effects of treatment in diabetes and nephrotic syndrome. Parathyroid hormone (PTH), which controls calcium levels, is often increased in kidney disease and is often checked to see if enough calcium and vitamin D are being taken to prevent bone damage.
Cystatin C is another test that may be used as an alternative to creatinine and creatinine clearance to screen for and monitor kidney dysfunction in those with known or suspected kidney diseases. It may be especially useful in those cases where creatinine measurement is not appropriate; for instance, in those who have liver cirrhosis, are very obese, are malnourished or have a reduced muscle mass. Measuring Cystatin C may also be useful in the early detection of kidney disease when other parameters might still be normal, especially in the elderly.
If a structural problem or blockage is suspected, a picture 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. Various x-ray procedures can also be employed, such as an intravenous urogram, micturating cystogram, or renal arteriogram (or angiogram).
A biopsy can determine the cause of protein or blood in the urine and be used to monitor the effectiveness of treatment. Analyzing a small piece of kidney tissue can reveal the nature and extent of structural damage to a kidney. A biopsy, obtained using a biopsy needle and diagnostic imaging equipment, is often useful when disease of the glomerular filter is suspected.