Red Blood Cell Distribution Width (RDW) by Volume (RDW-V)
This test measures the variation in size of your red blood cells (RBCs). Healthy RBCs are generally similar in size, but this test helps identify when they differ significantly, which can signal certain blood conditions.
["RDW-V helps detect anemia or iron deficiency that affects RBC size uniformity."]
Key facts at a glance
- LOINC
- 100430-8
- Short code
- LRBA/CD3FC
- Synonyms
- Cells.LRBA+/T Cells NFr Bld FC
- Category
- chemistry
- Sample
- whole-blood
- Container
- EDTA (lavender/purple-top) anticoagulant tube; sodium heparin (green-top) tube is also acceptable for flow cytometry
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- flow-cytometry
- CPT
- 88184 (Flow cytometry, cell surface, cytoplasmic, or nuclear marker, technical component only; first marker); 88185 (each additional marker); 88187-88189 (interpretation)
- SNOMED
- 442940003 (Flow cytometry); 122448007 (CD3 positive T lymphocytes); 122550002 (LRBA protein)
- Specimen volume
- 3-5 mL of whole blood for adults; 1-3 mL for pediatric patients
- Stability
- Specimen should be processed within 24-48 hours of collection when stored at room temperature (18-25°C). Do not refrigerate or freeze whole blood as this may affect cell viability and marker expression. Samples should be analyzed as soon as possible, ideally within 24 hours.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 24–72 hours
- Order
- routine
Why Is This Test Done?
Your healthcare provider may order an RDW-V test to investigate symptoms like fatigue, pale skin, or shortness of breath. It’s also used to monitor conditions like anemia, vitamin deficiencies (such as iron or vitamin B12), or chronic diseases that affect red blood cell production.
What to Expect Before the Test
No special preparation is needed for this blood test. You’ll typically fast for 8–12 hours before drawing blood, but this is for other tests, not RDW-V. Bring any medications or questions to your appointment.
What Happens During the Test?
A healthcare professional will insert a needle into a vein in your arm to collect a small blood sample. You may feel a brief pinch, but it usually doesn’t cause discomfort. The test itself takes only a few minutes.
What Are Possible Results?
An elevated RDW-V may indicate conditions like anemia (due to iron deficiency, vitamin B12 deficiency, or other causes), chronic diseases, or certain cancers. A normal result doesn’t rule out all causes of RBC size variation, so your provider will consider other factors.
Reference range
Reference ranges for LRBA-expressing CD3+ T cells as a percentage of total lymphocytes (CD3+CD14-CD45+) are laboratory-specific and should be established by each institution. Generally, healthy adult donors show detectable LRBA expression on the majority of CD3+ T cells. Consult laboratory-specific reference interval report.N/A
No special patient preparation required. No fasting necessary. Patients should be well-hydrated prior to venipuncture. Recent immunotherapy, immunosuppressive therapy, or hematopoietic stem cell transplantation may affect results and should be documented on the requisition. Inform the laboratory of any recent blood transfusions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
RDW-V is a key marker in diagnosing and managing anemia and other blood disorders. High levels often signal underlying issues like poor nutrient absorption, bone marrow problems, or long-term illnesses. It’s also used to assess treatment responses in conditions like pernicious anemia or thalassemia.
Short name
RDW-V
Frequently asked questions
What causes an elevated RDW-V?
What does a normal RDW-V mean?
Can RDW-V be affected by medications?
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 16, 2026. · Read our editorial policy