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Red Blood Cell Casts, Urine

Published: August 9, 2026Updated: August 17, 2026

Urine RBC casts are red blood cells trapped in tiny protein structures formed inside kidney tubules. Their presence can be associated with kidney inflammation or bleeding.

Quick summary

["RBC casts in urine may suggest bleeding or inflammation originating within the kidneys."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
88970-9
Short code
RBC Casts #/area UrnS
Synonyms
RBC Casts #/area UrnS
Category
liver
Sample
urine
Container
Sterile urine container
Units
N/A
Ref low
10
Ref high
40
Critical range
2 N/A – 7 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What is this test?

This test looks for red blood cell casts in a urine sample. Casts are cylindrical structures that form inside the kidney's filtering tubules, and their shape can help show where kidney bleeding or injury is occurring.

Why might I need this test?

Your clinician may order this as part of a urinalysis when you have blood or protein in your urine, swelling, decreased urination, or other signs of possible kidney disease. It is often interpreted together with urine protein, blood, and other urine microscopy findings.

How is the test performed?

A urine specimen is examined in the laboratory, usually by microscopic analysis after the sample is prepared. The laboratory checks for red blood cells and protein-based casts and reports whether RBC casts are present.

How do I prepare for the test?

Follow your clinician's instructions about collecting the urine. A clean-catch, first-morning specimen may be requested, and the sample is usually provided in a sterile urine container.

Reference range

Adult: 10-40 U/LN/A

Specimen: urine

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine RBC casts

Frequently asked questions

What does an RBC cast mean?
An RBC cast means that red blood cells have become embedded in a protein structure formed inside a kidney tubule. This often points toward bleeding or inflammation within the kidney rather than bleeding from somewhere lower in the urinary tract.
Does one RBC cast confirm a specific kidney disease?
No. RBC casts can occur with several kidney conditions and do not identify one diagnosis by themselves. Your clinician will consider the complete urinalysis, kidney function tests, symptoms, and medical history.
Can RBC casts be found without visible blood in the urine?
Yes. The urine may appear normal to the eye even when red blood cells or RBC casts are detected microscopically. Follow-up testing may be needed to determine the cause.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy