Renal tubular epithelial casts; Waxy casts; Casts in the urine; Fatty casts; Red blood cell casts; White blood cell casts. Casts are formed in the tubules of the kidney when the tubules secrete a protein called Tamm-Horsfall protein. The origin of the casts causes them to take on a tubular or hotdog-like shape. These casts are known as hyaline casts and can be present in normal adults on the order of 0-5 per LPF.
Urinary casts are tiny tube-shaped particles that can be found when urine is examined under the microscope during a test called a urinalysis. Urinary casts may be made up of white blood cells, red blood cells, kidney cells, or substances such as protein or fat. The content of a cast can help tell your health care provider whether your kidney is healthy or abnormal.
How the Test is Performed
The urine sample you provide may need to be from your first-morning urine. The sample needs to be taken to the lab within 1 hour.
A clean-catch urine sample is needed. The clean-catch method is used to prevent germs from the penis or vagina from getting into a urine sample. To collect your urine, the provider may give you a special clean-catch kit that contains a cleansing solution and sterile wipes. Follow instructions exactly so that the results are accurate.
How to Prepare for the Test
No special preparation is needed.
How the Test will Feel
The test involves only normal urination. There is no discomfort.
Why the Test is Performed
Your provider may order this test to see if your kidneys are working properly. It may also be ordered to check for certain conditions, such as:
- Glomerular disease
- Interstitial kidney disease
- Kidney infections
Normal Results
The absence of cellular casts or the presence of a few hyaline casts is normal. The examples above are common measurements for the results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal results may include:
- Fatty casts are seen in people who have lipids in urine. This is most often a complication of nephrotic syndrome.
- Granular casts are a sign of many types of kidney diseases.
- Red blood cell casts mean there is a microscopic amount of bleeding from the kidney. They are seen in many kidney diseases.
- Renal tubular epithelial cell casts reflect damage to tubule cells in the kidney. These casts are seen in conditions such as renal tubular necrosis, viral disease (such as CMV nephritis ), and kidney transplant rejection.
- Waxy casts can be found in people with advanced kidney disease and chronic kidney failure.
- White blood cell (WBC) casts are more common with acute kidney infections.
Your provider will tell you more about your results.
Risks
There are no risks with this test.
|
Type
|
Description
|
Significance
|
|---|---|---|
|
Plain casts
|
||
|
Hyaline |
Glycoprotein matrix consisting mainly of Tamm-Horsfall protein secreted by tubules |
Nonspecific
Can be present in normal urine or patients with low urine flow (eg, due to dehydration, after diuretic therapy), physiologic stress, acute renal disorder plus other abnormalities, or a chronic renal disorder (as broadcasts formed in dilated tubules) |
|
Waxy |
Glycoprotein matrix with degraded protein
Formed in atrophic tubules
Highly refractile with a waxy appearance |
Present in advanced chronic kidney disease |
|
Casts with inclusions
|
||
|
RBC |
Glycoprotein matrix with RBCs
Often appears red-orange |
Virtually pathognomonic of glomerulonephritis
Occurs extremely rarely in patients with cortical necrosis or acute tubular injury or runners with hematuria |
|
Epithelial cell |
Protein matrix variably filled with tubular cells |
Occurs in acute tubular injury, glomerulonephritis, or nephrotic syndrome |
|
WBC |
Protein matrix variably filled with WBCs |
Suggests pyelonephritis but can indicate other causes of tubulointerstitial inflammation
It May occur in proliferative glomerulonephritis |
|
Granular |
Glycoprotein matrix with protein or cellular debris
Often appears “muddy brown” |
Occasionally occurs after exercise or dehydration when renal function is normal
More often indicates acute tubular necrosis |
|
Pigment |
Tubular cell or granular casts with pigment stain |
Usually occurs in acute kidney injury due to hemolysis or rhabdomyolysis or in acute tubular necrosis |
|
Fatty |
Fat droplets or oval fat bodies (cholesterol produces a Maltese cross pattern in polarized light) |
It May occur in various types of tubulointerstitial disorders
In large numbers, strongly suggests that nephrotic syndrome |
|
Mixed |
Hyaline cast with various cells (eg, RBCs, WBCs, tubular cells) |
Usually occurs in proliferative glomerulonephritis |
|
Pseudocysts
|
||
|
|
Clumped urates, WBCs, bacteria, hair, glass fragments, cloth fiber, or artifacts |
Important not to confuse with true casts, which are cylindrical and shaped like renal tubules |
