Hyaline Casts in Urine: What They Are & When to Worry
Also known as: Hyaline cast, hyaline casts in urine
A hyaline cast is a clear, cylinder-shaped structure made of a protein called Tamm-Horsfall protein that forms in the kidney's tubules and can be seen when urine is examined under a microscope. Hyaline casts are the most common type of urinary cast, and a small number (roughly 0–5 per low-power field) is considered normal, especially after exercise, dehydration, or fever. A larger number can occur with kidney stress or certain kidney diseases, so a persistently elevated count is generally interpreted by a clinician alongside the rest of your urinalysis and kidney function tests.
Hyaline Casts normal range
| Category | Range (casts/LPF (low-power field)) |
|---|---|
| Normal | 0–5 per LPFReference ranges vary by lab |
| Increased | > 5 per LPFOften benign but can reflect kidney stress |
Reference ranges vary by laboratory. Use the range printed on your own report as the definitive comparison.
What high Hyaline Casts can mean
- Dehydration, fever, or recent strenuous exercise (common benign causes)
- Diuretic (water pill) use
- Kidney stress from an underlying condition, including some forms of kidney disease
- Can be seen transiently with normal kidney function
What low Hyaline Casts can mean
- A low or absent hyaline cast count is a normal, expected finding
- There is no clinical concern about having too few hyaline casts
What to do about an abnormal result
- A small number of hyaline casts is usually not a concern, especially with a clear explanation like dehydration, fever, or exercise.
- A larger number, especially with protein in the urine or other abnormal urinalysis findings, may prompt your doctor to check kidney function tests like eGFR and creatinine.
- Make sure you're well hydrated before testing, since dehydration is a common benign cause of a mildly elevated count.
- Don't self-diagnose from one result — hyaline casts are interpreted by a clinician alongside your full urinalysis and kidney function.
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Frequently asked questions
What is a hyaline cast?
A hyaline cast is a clear, cylinder-shaped structure made of a protein (Tamm-Horsfall protein) that forms inside the kidney's tubules and washes into the urine, where it's identified under a microscope during a urinalysis. Hyaline casts are the most common type of cast, and a small number is considered a normal finding, particularly after exercise, dehydration, or fever.
Should I be worried about hyaline casts in my urine?
A small number of hyaline casts is usually not a cause for concern and is often related to dehydration, fever, or recent exercise rather than kidney disease. A higher number, especially alongside protein in the urine or other abnormal findings, is worth discussing with your doctor, who may check kidney function tests to see if follow-up is needed.
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Medically reviewed by Antonieta Rueda, MD and Kyle R. Toth, MD · Last reviewed July 6, 2026
This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or your lab results.