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B-cell Lymphocyte Count (Absolute Count)

Published: August 9, 2026Updated: August 16, 2026

This test measures the number of B cells, a type of white blood cell important for producing antibodies that help fight infections.

Quick summary

["B cells help your immune system defend against germs and diseases."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
8117-4
Short code
CD19
Synonyms
CD19 Cells NFr Bld
Category
chemistry
Sample
whole-blood
Container
EDTA (lavender-top) blood collection tube
Units
N/A
Ref low
5
Ref high
15
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Flow cytometry using fluorescently labeled monoclonal antibodies against CD19 surface marker
CPT
86356
SNOMED
122574007
Specimen volume
3-5 mL whole blood; minimum 1 mL for pediatric samples
Stability
Room temperature: 24 hours; Refrigerated (2-8°C): 48 hours; Do not freeze. Best results within 6 hours of collection.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order this test to check for immune system problems, monitor conditions like chronic infections, or evaluate responses to treatments for diseases such as cancer or autoimmune disorders.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your vein (usually in your arm) to draw a blood sample. This is usually done in a clinic or lab.

What the Test Results Mean

Results show the count of B cells in your blood. Low counts may suggest immune deficiencies or certain cancers, while very high counts could indicate overactive immune responses or conditions like leukemia.

Common Conditions Monitored

This test helps diagnose or monitor conditions like B-cell lymphoma, chronic infections (e.g., HIV), or autoimmune diseases (e.g., lupus). It’s also used in cancer treatment follow-ups.

Reference range

CD19+ B lymphocytes: 5-15% of total lymphocytes; Absolute count: 90-660 cells/uLN/A

Specimen: whole-blood

No fasting required. Avoid strenuous exercise prior to collection. Inform laboratory of any recent immunotherapy, chemotherapy, or immunosuppressive medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

B-Cell Count

Frequently asked questions

What does a low B-cell count mean?
A low B-cell count may mean your immune system isn’t working as well as it should, which could increase your risk of infections. This might happen due to certain medications, immune disorders, or cancer treatments.
How often will I need this test?
Your doctor will determine how often you need this test based on your health condition, treatment plan, or symptoms. It could be done monthly, quarterly, or as needed.
Can I eat or drink before this test?
You can eat and drink normally before the test, as it only requires a blood draw. Avoiding food or fluids for a long time isn’t necessary unless your doctor specifies otherwise.
  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 16, 2026. · Read our editorial policy