Red Blood Cell Casts, Urine — Microscopy, Reported per High-Power Field
A urine microscopy test that looks for red blood cell casts, which are formed inside kidney tubules and may indicate kidney inflammation or bleeding.
["RBC casts in urine can be an important sign of kidney disease, especially inflammation of the kidney’s filtering units."]
Key facts at a glance
- LOINC
- 51790-4
- Short code
- RBC Casts #/area UrnS HPF
- Synonyms
- RBC Casts #/area UrnS HPF
- 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-hpf
- 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 under a microscope to identify red blood cell casts. Casts are structures that form inside the kidney’s tiny tubes, and RBC casts contain red blood cells.
Why might I need this test?
A clinician may order this test when urine tests show blood or protein, or when symptoms suggest a kidney or urinary tract condition. It can help distinguish bleeding within the kidney from blood entering the urine from another location.
How is the test performed?
A urine sample is collected and examined by a laboratory professional using microscopy. The number of RBC casts is generally reported in relation to the microscope’s high-power field.
How do I prepare for the test?
Follow any instructions provided by your clinician or laboratory. Often, a clean-catch, midstream urine sample is requested, and the sample should be labeled and delivered as directed so cells do not break down during transport.
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.
RBC casts may indicate bleeding and inflammation within the kidney, particularly when accompanied by urine blood, protein, or other abnormal findings. Possible causes include glomerulonephritis, other forms of kidney injury, or inflammation affecting the kidney’s filtering structures. Results should be interpreted by a clinician alongside symptoms and the rest of the urinalysis.
Short name
Urine RBC Casts
Frequently asked questions
What does a positive RBC cast result mean?
Is this the same as a blood test?
Do RBC casts always mean a serious illness?
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