Urinary casts

Definition

Urinary casts are tiny tube-shaped particles that can be found when urine is examined under the microscope during a test called 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.

Alternative Names

Hyaline casts; Granular casts; Renal tubular epithelial casts; Waxy casts; Casts in the urine; Fatty casts; Red blood cell casts; White blood cell casts

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 presence of a few hyaline casts is normal.

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 cytomegalovirus [CMV] nephritis), and kidney transplant rejection.
• Waxy casts can be found in people with advanced kidney disease and long-term (chronic) kidney failure.
• White blood cell (WBC) casts are common with acute kidney infections and interstitial nephritis.

Your provider will tell you more about your results.

Risks

There are no risks with this test.

References

Judd E, Sanders PW, Agarwal A. Diagnosis and clinical evaluation of acute kidney injury. In: Feehally J, Floege J, Tonelli M, Johnson RJ, eds. Comprehensive Clinical Nephrology. 6th ed. Philadelphia, PA: Elsevier; 2019:chap 68.

Riley RS, McPherson RA. Basic examination of the urine. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 28.