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Red Blood Cell Casts, Urine — Microscopy, Semi-quantitative

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

A urine microscopy test that detects and estimates red blood cells formed into casts, which may indicate inflammation or disease affecting the kidneys.

Quick summary

["Red blood cell casts in urine can suggest a kidney problem, especially inflammation of the kidney's filtering structures."]

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

Key facts at a glance

LOINC
33804-6
Short code
RBC Casts UrnS Ql Micro
Synonyms
RBC Casts UrnS Ql Micro
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
Method
microscopy-light
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 examines urine under a microscope to look for red blood cell casts. Casts are small structures that form inside kidney tubules and are released into the urine.

Why might I need this test?

A clinician may order this test when urine testing shows blood or red blood cells and kidney inflammation or disease is suspected. It is especially useful in evaluating conditions affecting the kidney's filtering units, called glomeruli.

How is the test performed?

A urine sample is prepared for microscopic examination, often by centrifuging it and examining the sediment. The laboratory checks for red blood cell casts and may estimate the amount or density observed.

How do I prepare for the test?

Follow your clinician's collection instructions, which may include a clean-catch, midstream urine sample. Fasting is generally not required, but tell the laboratory if you recently had a urinary tract infection, menstruation, or kidney symptoms.

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 red blood cell casts

Frequently asked questions

What does a red blood cell cast mean?
It means red blood cells have become trapped in a protein matrix formed inside a kidney tubule. This can occur with inflammation or injury affecting the kidney's filtering units.
Is this different from blood in the urine?
Yes. Blood in urine can come from many sources, while red blood cell casts are formed specifically within the kidney and therefore provide more specific information about kidney involvement.
Does an abnormal result always mean I have kidney disease?
No. The result must be considered with other findings, and it may also be influenced by temporary urinary tract inflammation or other clinical circumstances. Your clinician can explain what it means in your situation.
  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