Hyaline Casts

What Are They, Causes, Diagnosis, Treatment, and More

Author: Anna Hernández, MD

Editors: Ahaana Singh, Lisa Miklush, PhD, RN, CNS

Illustrator: Jillian Dunbar

What are hyaline casts?

Hyaline casts are the simplest and most common type of urinary cast. Urinary casts are microscopic clusters of urinary particles, such as cells, fat bodies, or microorganisms, wrapped in a protein matrix and found in the urine. Urinary casts serve as clinical indicators of kidney condition and can be assessed to determine the functioning of the kidneys. 

The kidneys are two bean-shaped organs located in the abdomen, at either side of the lower spine. They’re composed of millions of filtering units called nephrons. Each nephron is composed of a glomerulus (a ball-shaped network of blood vessels involved in the formation of urine) and kidney tubules (a series of tubules that reabsorb and modify urine composition according to the body’s necessities).

Cast formation takes place in the final portion of the kidney tubules, which consists of the distal convoluted tubules and collecting ducts. It results from the precipitation of Tamm–Horsfall protein (also known as uromodulin) which is secreted by the epithelial tubule cells. Aggregation of Tamm–Horsfall protein into a protein matrix can then attract the adhesion of other tubular particles (e.g. cells, bile, hemoglobin, albumin, immunoglobulins). Once the urinary casts have developed, they can dislodge from the tubular lumen and travel through the urinary tract, before being excreted in the urine.

Depending on the composition, urinary casts can be categorized into cellular casts and non-cellular casts. Examples of cellular casts include renal tubular epithelial casts, red blood cell (RBC) casts, and white blood cell (WBC) casts. Examples of non-cellular casts include hyaline casts, granular casts, fatty casts, and waxy casts, among others. 

What do hyaline casts in urine indicate?

Hyaline casts are considered to be a nonspecific finding— they can be found in both healthy individuals and individuals with pathological conditions. The presence of hyaline casts typically indicates a decreased or sluggish urine flow, which can be a result of strenuous exercise, diuretic medications, severe vomiting, or fever. In combination with other clinical findings, large amounts of hyaline casts may indicate kidney damage due to decreased blood flow to the kidneys. 

Normally, the presence of casts in the urine is considered to be an unusual finding. However, small amounts of hyaline casts (between 0–2 casts per low power field of the microscope) may be detected in the urine of healthy individuals without necessarily indicating a serious condition like kidney disease. In fact, hyaline casts are the only casts that should be detected in the urine in absence of kidney, or renal, disease. 

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What causes hyaline casts?

Hyaline casts are composed of aggregated Tamm-Horsfall protein in the tubular lumen of the kidney. Increased precipitation of Tamm-Horsfall protein can be caused by a variety of factors:

  • Increased acidity in the urine. 

  • Decreased or sluggish urine flow.

  • Highly concentrated urine. 

Consequently, it’s possible to detect a greater amount of hyaline casts after strenuous exercise, during treatment with certain types of diuretic medications, or in individuals with severe vomiting or fever (indicative of dehydration). In addition, hyaline casts may appear alone or in association with other types of casts in certain pathological conditions, including acute kidney injury.

How do you diagnose hyaline casts?

Hyaline casts can be diagnosed through urinalysis

  • Urinary sediment microscopy 

  1. Centrifugation of a urine sample to separate urine sediment (e.g., casts, cells, pathogenic microorganisms) from fluid.

  2. Small drop of urine sediment is examined under a microscope.

    1. Hyaline casts can be identified as clear, tiny tubule-shaped particles.

    2. Phase contrast microscopy may be used to enhance the contrast in order to better visualize the particles.

    3. Microscopy stains or dim lighting may also be used to help identify particles. 

How do you treat hyaline casts?

Oftentimes, hyaline casts are not always considered to be an unusual finding, and thus may not require treatment at all. In cases of kidney damage, however, additional treatment may be required. 

  • Hyaline casts in healthy individuals often do not require any treatment.

  • In individuals with kidney damage treatment should be focused on treating the specific cause of renal function.

Frequently Asked Questions

Are hyaline casts dangerous?

Hyaline casts are typically not considered a dangerous finding. Unlike hyaline casts, other types of urinary casts are generally associated with kidney disease. For instance, epithelial cell casts reflect severe damage and death of the tubule cells, which is also known as tubular necrosis. In most cases, red blood cell casts reflect damage to the glomerulus, known as glomerulonephritis, or the presence of a microscopic bleeding within the kidney. White blood cell casts are typically associated with an underlying kidney infection (such as pyelonephritis) or inflammatory processes. Finally, fatty casts are typically detected in individuals with nephrotic syndrome, which causes proteinuria (excess protein in the urine), along with tissue swelling, low blood protein levels, and increased blood levels of cholesterol.

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Related links

Acute pyelonephritis
High Yield: Nephrotic syndromes
Prerenal azotemia
Renal anatomy and physiology

Resources for research and reference

Cavanaugh, C. & Perazella, M. A. (2018). Urine Sediment Examination in the Diagnosis and Management of Kidney Disease: Core Curriculum 2019. American Journal of Kidney Diseases, 73(2): 258–272. DOI: 10.1053/j.ajkd.2018.07.012

Dvanajscak, Z., Cossey, L. N., & Larsen, C. P. (2020). A Practical Approach to the Pathology of Renal Intratubular Casts. Seminars in Diagnostic Pathology, 37(3): 127–134. DOI: 10.1053/j.semdp.2020.02.001 

Ringsrud, K. M. (2001). Casts in the Urine Sediment. Laboratory Medicine, 32(4): 191–193. DOI: 10.1309/kj5e-v5fe-mahr-kxt2