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Blood Test Tracker

Urine Hyaline Casts

A count of hyaline casts, tiny protein tubes in urine that are often harmless, especially after exercise or when you are dehydrated.

AI-verified against cited sources. Awaiting expert reviewLOINC 5796-8

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What it is

Casts are tiny tube-shaped particles that form in the kidney's small tubes and wash out in urine. Hyaline casts are the most common type. They are made mostly of a protein the kidneys release naturally, called uromodulin or Tamm-Horsfall protein, and they look clear under a microscope. Labs count casts per low-power field (LPF) as part of a complete urinalysis.

Why it matters

A few hyaline casts are common in healthy people and often come from dehydration, hard exercise or fever. They matter more when the count stays high on repeat samples, or when they show up with other findings such as protein or blood in the urine. Your clinician reads this result alongside your other urine and kidney tests. Quest and Labcorp list none seen as the expected result, so even a small number can be flagged.

If it’s high

Hyaline casts mean the sample contained clear protein casts. A few are common and often harmless. A higher count can come from dehydration or hard exercise, and a repeat sample is a common next step. Your clinician can tell you whether other results make it worth a closer look.

Common causes

  • Dehydration or concentrated urine
  • Strenuous exercise (in one small study, 2 of 20 ultra-marathon finishers had more than 5 per LPF afterward, though the change was not statistically significant)
  • Fever or illness
  • Reduced blood flow to the kidneys, which can show hyaline casts and little else
  • Kidney conditions, including long-term kidney disease

What can help

  • Drink fluids as your clinician advises, unless you have been told to limit them
  • Tell your clinician about recent hard exercise, fever or illness
  • Ask whether to repeat the urine test when you are rested and well hydrated

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: up to 0 /LPF. Source: Quest Diagnostics, Labcorp.

What can affect your result

  • Hydration and how concentrated the urine is
  • Strenuous exercise and fever
  • Time between collection and testing, and how acidic, alkaline or dilute the urine is
  • First-morning versus second-morning and midstream collection
  • The method (manual microscopy per LPF, or an automated analyzer) and the person reading the slide
  • Dehydration, strenuous exercise and fever can raise the number of hyaline casts, so the same person can have different counts on different days.
  • Urine that sits too long, or is alkaline or very dilute, can break casts down, so counts read low. A review notes that European guidance asks labs to examine urine within about 1 hour at room temperature or 4 hours if refrigerated.
  • Hyaline casts are see-through and easy to miss. Counts depend on the microscope technique and the person reading the slide, and automated analyzers count per microliter, which does not convert directly to per LPF.

A fresh midstream (clean-catch) sample is preferred. A second-morning sample is often better than the first void of the day, because casts can break down while urine sits in the bladder overnight. Reflects the sample you gave. It can change from day to day with hydration, exercise and illness.

When to talk to a clinician

A hyaline cast result on its own rarely needs urgent care. Ask the clinician who ordered the test what it means. Contact them sooner if casts are reported with protein or blood in your urine, swelling, or much less urine than usual. If you have chest pain, trouble breathing or confusion, call 911 or your local emergency number.

Questions you could ask

  • Which parts of my urine report should I watch over time?
  • Could dehydration or recent exercise explain this?
  • Should we repeat the urine test when I am well hydrated?
  • How do these casts fit with my urine protein, blood and kidney blood tests?

Questions people ask

Are hyaline casts a sign of kidney disease?

Usually not on their own. A few hyaline casts are common, and hard exercise, dehydration or fever can raise the count. They matter more when the count stays high on repeat tests, or when protein, blood or other casts are present. Your clinician reads the whole urine report.

Why was a small number flagged if a few are normal?

Quest and Labcorp list none seen as the expected result for casts, so any cast gets flagged. Some hospital labs allow up to 2 per LPF. Check the range printed on your report and ask your clinician what it means for you.

Can exercise or dehydration cause hyaline casts?

Yes. Hard exercise, dehydration and fever are all linked to more hyaline casts. A repeat sample after rest and fluids often shows fewer.

Show the science and sources

For clinicians and researchers

Hyaline casts are a colorless matrix of uromodulin (Tamm-Horsfall protein) with a low refractive index, so they are easiest to see under reduced light or phase contrast. A review table lists increases with strenuous exercise, dehydration and fever, and notes that the sediment in prerenal acute kidney injury is typically unremarkable or shows hyaline casts. A review recommends counting under low power (100x) across at least 10 fields (ideally 20) after spinning about 10 mL at 400 g for at least 5 minutes, and examining urine within about 1 hour at room temperature or 4 hours if refrigerated, because alkaline pH and low osmolality lyse casts. In a 2025 study of 20 ultra-marathon finishers, 18 stayed in the 0-5 per LPF bin afterward, one reached 6-10 and one went above 25. Reference intervals differ: Quest prints 'None seen' (result code 30010400, LOINC 5796-8), Labcorp prints 'None seen' per LPF for casts overall with the type named separately, and three hospital tables print 0-2 per LPF. LOINC also defines hyaline casts per high-power field (46135-0) and per volume for automated counts (for example 51484-4). The per-microliter values cannot be converted to per-LPF without the lab's field and prep, so only per-LPF is modeled here.

LOINC 5796-8 (primary), 88966-7, 33223-9, 25162-9. Specimen: urine.

Sources

  1. Urinalysis, Complete (test code 5463), Quest Diagnostics
  2. Urinalysis, Complete (test 003772), sample patient report, Labcorp (2026)
  3. Urinary casts (MedlinePlus Medical Encyclopedia), MedlinePlus, U.S. National Library of Medicine
  4. Diagnostic Utility of Urine Microscopy in Kidney Diseases, Indian Journal of Nephrology (2024)
  5. Athletic pseudonephritis in male cross-country ultra-marathoners: a comparative observational study, Frontiers in Physiology (2025)
  6. Navigating complex cardiac complications: A case report of alcoholic cardiomyopathy and right atrial thrombosis, Medicine (Baltimore) (2024)
  7. Purple catheter syndrome (PUBS): a mystery in a post stroke patient with Klebsiella, BMC Urology (2026)
  8. Lorazepam-Induced Orthostatic Hypotension and Secondary Headache in a Low Blood Pressure Phenotype, Cureus (2025)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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