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Casts in Urine (Urine Casts): What Your Result Means

What urine casts are, how they form in the kidney, when a few hyaline casts are a normal finding, and which cast findings point to the kidneys.

Published

August 10, 2024

Last updated

November 2, 2026

Read time

3 min read

Medically reviewed by

Rhonda Collins, FNP-C

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Urine casts are tiny tube-shaped particles that form inside the kidney’s tubules and wash out in urine, where they can be seen under the microscope during a urinalysis. A few hyaline casts can be a normal finding. Casts that contain cells usually point to a process in the kidney itself ^[1][2].

What are urine casts?

Casts form in the last segments of the kidney’s tubules, the distal convoluted tubule and the collecting duct. They are a gel of a protein called Tamm-Horsfall mucoprotein (also called uromodulin) that traps whatever is in the tubule at the time, and they keep the cylindrical shape of the tubule they formed in ^[2]. They form more readily when urine is concentrated or flowing slowly, or when urine pH is very low ^[2].

A cast may contain white blood cells, red blood cells, kidney cells, or substances such as protein or fat ^[1]. Because casts can only form inside a kidney tubule, their contents help localize a urinalysis finding to the kidney rather than the bladder or urethra ^[2].

How are urine casts tested?

Casts are part of the microscopic exam of a urinalysis, in which the lab looks at the urine sample for cells, crystals, casts, mucus, bacteria, and other substances ^[3]. A clean-catch sample is used, and it should reach the lab within about an hour ^[1]. The report lists the casts seen, often by type, such as hyaline or granular.

Casts are different from mucus threads, which the same exam can also report. Our guide to mucus in urine explains how the two differ.

What is a normal urine casts result?

Urine normally has no cellular casts, and a few hyaline casts are a normal finding ^[1]. Hyaline casts are the most common type. They are made of protein and can follow dehydration or strenuous exercise. They can also be seen with chronic kidney disease ^[1][4].

What do abnormal urine casts mean?

Casts beyond a few hyaline casts usually suggest a kidney condition, and the type of cast points to which kind ^[1][4]:

• Red blood cell casts mean a small amount of bleeding from the kidney and are seen in many kidney diseases ^[1].
• White blood cell casts are common with kidney infections and interstitial nephritis ^[1].
• Granular casts may indicate injury to the kidney tubules ^[4].

Our urine cast types page covers every cast type, including waxy, fatty, and epithelial casts, and what each is linked to.

Casts are read with the rest of the urinalysis, especially urine protein and urine red blood cells, and with kidney blood tests such as creatinine and eGFR. Talk with your clinician about any cast other than a few hyaline casts, since it usually calls for a closer look at kidney function.

Urine casts testing with Mito

The Urinalysis, Complete Test with Reflex to Urine Culture includes a microscopic exam that reports hyaline casts, granular casts, and a general casts result, along with crystals, bacteria, and yeast. Check the product page for current pricing and availability.

Related Urine Casts Resources

• How to Improve Your Urine Casts Level Naturally

References

1. MedlinePlus Medical Encyclopedia: Urinary casts
2. Simerville JA, Maxted WC, Pahira JJ. Urinalysis: A Comprehensive Review. Am Fam Physician. 2005
3. MedlinePlus Medical Encyclopedia: Urinalysis
4. Hitzeman N, Greer D, Carpio E. Office-Based Urinalysis: A Comprehensive Review. Am Fam Physician. 2022