Red Blood Cell Casts, Urine
A urine microscopy test that looks for red blood cell casts, which can form when the kidneys' filtering units are inflamed or injured.
["Red blood cell casts in urine may suggest kidney inflammation, especially when blood or protein is also present."]
Key facts at a glance
- LOINC
- 33229-6
- Short code
- RBC Casts #/area Ur Comp Assist
- Synonyms
- RBC Casts #/area Ur Comp Assist
- 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
- computer-assisted
- 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 a urine sample for red blood cell casts. Casts are tube-shaped structures that form inside the kidney's filtering units and are released into the urine.
Why might I need this test?
Your clinician may order this test if you have blood in the urine, swelling, high blood pressure, or other signs of kidney or blood-vessel inflammation. It may also be used to help distinguish a kidney problem from a urinary tract problem.
How is the test performed?
A urine sample is examined using microscopy, sometimes with computer-assisted identification of urine particles. The laboratory reports whether red blood cell casts are present and may estimate the amount seen.
How do I prepare for the test?
Follow your clinician's instructions about when and how to collect the urine. A clean-catch midstream sample is often requested, and the laboratory may provide a sterile container and specific collection instructions.
Reference range
Adult: 10-40 U/LN/A
No special preparation required. Stay well hydrated.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Red blood cell casts generally suggest bleeding and inflammation within the kidneys, as may occur with glomerulonephritis or certain systemic blood-vessel conditions. They are less likely to result from bleeding only in the lower urinary tract. Results should be interpreted with urine blood and protein findings, symptoms, kidney function tests, and other clinical information.
Short name
Urine RBC casts
Frequently asked questions
What does a red blood cell cast mean?
Are red blood cell casts the same as blood in the urine?
Does one abnormal result confirm a kidney disease?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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