CD21 Cell Count in Peripheral Blood (Fluid)
This test measures the number of CD21-positive cells, which are a type of immune system cell found in blood. CD21 is a protein involved in immune function, often assessed in conditions affecting the immune system.
["CD21 cells help your immune system recognize and respond to infections and other threats."]
Key facts at a glance
- LOINC
- 57419-4
- Short code
- CD21BF
- Synonyms
- CD21 Cells NFr Fld
- Category
- chemistry
- Sample
- serum
- Container
- Sterile body fluid collection container; lavender-top (EDTA) tube preferred for anticoagulated samples
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Flow cytometry
- CPT
- 88184
- SNOMED
- 39754003
- Specimen volume
- 1-5 mL of body fluid depending on source; minimum 1 mL recommended for adequate flow cytometry analysis
- Stability
- Maintain at room temperature (18-25°C); analyze within 24 hours of collection for optimal CD21 antigen detection
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
What Is CD21 Used For?
CD21 cell counts are primarily used to evaluate immune function, particularly in diagnosing and monitoring conditions like immune deficiencies, certain cancers (e.g., lymphoproliferative disorders), or autoimmune diseases. It may also be part of a broader evaluation for patients with recurrent infections or unexplained immune issues.
How Is This Test Performed?
A small blood sample is drawn from a vein, typically in your arm. The blood is then analyzed in a lab to count CD21-positive cells, which are part of the immune system’s B-cell lineage. Results are compared to standard reference ranges for healthy adults.
Why Might You Need This Test?
Your healthcare provider may order this test if you have symptoms like frequent infections, unusual fatigue, or if you’ve been diagnosed with a condition that affects immune cells. It can also help monitor treatment responses in certain cancers or immune disorders.
What Do Results Mean?
Results may indicate low or high CD21 cell counts, which can signal immune dysfunction. However, reference ranges can vary by lab, so your provider will interpret results in the context of your overall health and medical history.
Reference range
Reference range established by individual laboratory; results expressed as percentage of total lymphocytes or absolute count (cells/μL)N/A
No special patient preparation required. Sample should be processed within 24 hours of collection for optimal viability of lymphocyte markers.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: CD21 Cell Counts Play a Key Role in Diagnosing and Managing Immune-Related Disorders
Short name
CD21 Cells
Frequently asked questions
Why do doctors check CD21 levels?
What causes low or high CD21 cell counts?
Can diet or lifestyle affect CD21 test results?
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