Hyaline cast; Urinary casts; Renal tubular casts; Waxy casts; Casts in the urine; Fatty casts; Epithelial casts
Tubules in the kidneys secrete proteins. Under some circumstances, these proteins precipitate out to form little cylindrical impressions of the tubules called casts. If anything is present in the tubules at the time, it gets trapped in the protein casts. This offers a “snap shot” of the tubular lumen at the time of cast formation.
How the test is performed
Collect a “clean-catch” (midstream) urine sample. To obtain a clean-catch sample, men or boys should wipe clean the head of the penis. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well. As you start to urinate, allow a small amount to fall into the toilet bowl (this clears the urethra of contaminants). Then, in a clean container, catch about 1 to 2 ounces of urine and remove the container from the urine stream. Give the container to the health care provider or assistant.
In infants, thoroughly wash the area around the urethra. Open a Urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant. For males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Place a diaper over the infant (bag and all). Check your baby frequently and remove the bag after the infant has urinated into it. For active infants, this procedure may take a couple of attempts - lively infants can displace the bag, causing an inability to obtain the specimen. The urine is drained into a container for transport back to the health care provider.
How to prepare for the test
No special preparation is necessary for this test, but if the collection is being taken from an infant, a couple of extra collection bags may be necessary.
How the test will feel
The test involves only normal urination, and there is no discomfort.
Why the test is performed
The test is performed to see whether the kidneys are functioning properly and to check for certain conditions, such as kidney infections, glomerular diseases, and interstitial kidney diseases.
There are different types of casts. (See below.) The presence of a few “hyaline” casts is normal.
What abnormal results mean
Abnormal results may include:
- Hyaline casts - these casts are made of the protein itself. They are usually caused by dehydration, exercise, or diuretic medicines.
- Granular casts - these casts include prominent granules and indicate an underlying kidney disease. However, they are non-specific and may be present with diverse kidney disorders.
- Fatty casts - these result when fatty (lipid) material is incorporated into the cast from lipid-laden tubular cells. Fatty casts are seen in the condition of lipiduria (lipids in urine), usually as a complication of nephrotic syndrome.
- Red cell casts - these signify bleeding into the tubule from the glomerulus. They are seen in many diseases affecting the glomerulus, such as IgA nephropathy, lupus nephritis, Goodpasture’s syndrome , and Wegener’s Granulomatosis. Red cell casts may degenerate and appear in the urine as reddish-brown, coarsely granular casts, called blood or hemoglobin casts.
- White blood cell (WBC) casts - these are more common in interstitial cell kidney disease, such as interstitial inflammation, pyelonephritis, and parenchymal infection.
- Renal tubular epithelial cell casts - these reflect damage to the tubules. They are seen in renal tubular necrosis (for example, caused by nephrotoxic drugs, heavy metal poisoning, or ethylene glycol), viral disease (such as CMV nephritis), and with transplant rejection.
- Waxy casts - these casts are associated with advanced kidney disease and chronic kidney failure.
This test may also show:
- Acute nephritic syndrome
- Glomerulonephritis - chronic
- Glomerulonephritis - post-streptococcal
- Glomerulonephritis - rapidly progressive
- Complicated urinary tract infection
- Necrotizing vasculitis
- Primary amyloid
- Secondary amyloid
- Systemic lupus erythematosus
What the risks are
There are no risks.
The best way to look for casts is to examine freshly voided urine, preferably the first morning urine sample.
by Sharon M. Smith, M.D.