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CD21 on Blast Cells, Number Fraction — Specimen

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

Measures the proportion of blast cells that express CD21, a marker found on many B lymphocytes. It may help classify acute leukemia and other lymphoid disorders.

Quick summary

["This test helps determine whether abnormal immature blood cells show features of B-cell lineage."]

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

Key facts at a glance

LOINC
51117-0
Short code
CD21 Blasts/Blasts NFr Spec
Synonyms
CD21 Blasts/Blasts NFr Spec
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

This laboratory test measures the fraction of blast cells that express CD21. Blasts are immature blood cells, and CD21 is a surface protein present on many cells of B-cell lineage.

Why might I need this test?

This test may be used during the evaluation of acute leukemia, lymphoma, or other blood disorders. It can help determine whether a population of abnormal blasts has features consistent with B cells, usually as part of a broader flow-cytometry panel.

How is the test performed?

Cells from the submitted specimen, often blood or bone marrow, are stained with antibodies directed against CD21. Flow cytometry is typically used to determine the proportion of blast cells carrying the marker.

How do I prepare for the test?

No special preparation is usually required. Follow the instructions provided by the laboratory or your healthcare professional, particularly if bone marrow or another procedure is involved in collecting the specimen.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

CD21 on blast cells

Frequently asked questions

What does a positive CD21 result mean?
It means that the tested blast cells carry the CD21 marker. This can support B-cell lineage but does not independently establish a specific cancer or diagnosis.
Is this the same as a CD21 blood count?
No. This test evaluates CD21 on blast cells as part of cell identification, usually by flow cytometry, rather than measuring soluble CD21 in the blood.
Can CD21 alone diagnose leukemia?
No. Leukemia classification generally uses several markers, the appearance and number of abnormal cells, genetic or molecular findings when appropriate, and the clinical picture.
  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