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Immature B-Lymphocyte Number Fraction, Whole Blood

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

Measures the proportion of immature B lymphocytes in a whole-blood sample, usually to evaluate B-cell development or maturation.

Quick summary

["This test shows how many developing B cells are present in the blood."]

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

Key facts at a glance

LOINC
34920-9
Short code
Ib Lymphs NFr Bld
Synonyms
Ib Lymphs NFr Bld
Category
liver
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What is this test?

This test measures immature B lymphocytes, which are early-stage B cells that have not yet fully matured. The result is reported as a number fraction, or the proportion of these cells in the blood.

Why might I need this test?

It may be used to evaluate suspected immune-system or blood-cell disorders, particularly when B-cell development or maturation is in question. Results are interpreted together with other blood counts, symptoms, and medical history.

How is the test performed?

A whole-blood sample is collected, usually from a vein, and the immature B cells are identified and counted using specialized laboratory testing, often flow cytometry.

How do I prepare for the test?

No special preparation is usually required. Tell the healthcare team if you recently received chemotherapy, immunotherapy, a blood-cell transplant, or medicines that may affect the immune system.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

An increased proportion of immature B cells may occur when B-cell production is elevated or when cells are not maturing normally. A lower proportion may reflect reduced B-cell production, impaired maturation, or the effects of treatment. The result should be interpreted by a clinician because age, clinical condition, and other blood-cell findings can affect its meaning.

Short name

Immature B-cell percentage

Frequently asked questions

What does immature B lymphocyte number fraction mean?
It is the proportion of immature B cells found in the blood sample. It is a laboratory measurement rather than a diagnosis by itself.
Is this the same as a routine lymphocyte count?
No. A routine lymphocyte count may include mature and immature lymphocytes together, while this test specifically identifies the immature B-cell population.
Do I need to do anything special before the test?
Usually no special preparation is needed. Ask the laboratory or healthcare team if you have recently had treatments that could affect blood-cell development.
  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