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Test Code RBCS Relative B-Cell Subset Analysis Percentage

Useful For

Screening for humoral or combined immunodeficiencies, including common variable immunodeficiency (CVID), hyper IgM syndrome, among others, where B-cell subset distribution information is desired


Assessing B-cell subset reconstitution after hematopoietic cell (HCT) or bone marrow transplant


Assessing B-cell subset reconstitution following recovery of B cells after B-cell-depleting immunotherapy

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
CVID CVID Confirmation Flow Panel Yes No

Testing Algorithm

This test should be ordered only when percentages (relative distribution of B cell subsets within the total B-cell population) are needed for the reportable B-cell subsets. If both percentages and absolute counts are needed for the reportable B-cell subsets, order IABCS / B-Cell Phenotyping Profile for Immunodeficiency and Immune Competence Assessment, Blood.

Method Name

Fluorescent Flow Cytometry

Reporting Name

Relative B Cell Subset Analysis %

Specimen Type

Whole Blood EDTA

Specimen Required

It is recommended that specimens arrive within 24 hours of draw. Specimens are required to be received in the laboratory on weekdays and by 4 p.m. on Friday. No weekend processing. Draw and package specimens as close to shipping time as possible. Ship specimens overnight.

For serial monitoring, we recommend that specimen draws be performed at the same time of day.


Specimen Type: Whole blood

Container/Tube: Lavender top (EDTA)

Specimen Volume:

≤14 years: 4 mL

>14 years: 10 mL

Collection Instructions:

1. Send specimen in original tube. Do not aliquot.

2. Label specimen as blood for RBCS / Relative B Cell Subset Analysis Percentage.

Additional Information: Ordering physician's name and phone number are required.

Specimen Minimum Volume

≤14 years: 3 mL; >14 years: 5 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Refrigerated 48 hours

Clinical Information

The adaptive immune response includes both cell-mediated (mediated by T cells and NK cells) and humoral immunity (mediated by B cells). After antigen recognition and maturation in secondary lymphoid organs, some antigen-specific B cells terminally differentiate into antibody-secreting plasma cells or become memory B cells. Memory B cells are of 3 subsets: marginal zone B cells (MZ or nonswitched memory), class-switched memory B cells, and IgM-only memory B cells. Decreased B-cell numbers, B-cell function, or both, result in immune deficiency states and increased susceptibility to infections. These decreases may be either primary (genetic) or secondary. Secondary causes include medications, malignancies, infections, and autoimmune disorders.


Common variable immunodeficiency (CVID), a disorder of B-cell function, is the most prevalent primary immunodeficiency with a prevalence of 1:25,000 to 1:50,000.(1) CVID has a bimodal presentation with a subset of patients presenting in early childhood and a second set presenting between 15 and 40 years of age, or occasionally even later. Four different genetic defects have been associated with CVID, including mutations in the ICOS, CD19, BAFF-R, and TACI genes. The first 3 genetic defects account for approximately 1% to 2%, and TACI mutations account for 8% to 15% of CVID cases.


CVID is characterized by hypogammaglobulinemia usually involving most or all of the Ig classes (IgG, IgA, IgM, and IgE), impaired functional antibody responses, and recurrent sinopulmonary infections.(1,2) B-cell numbers may be normal or decreased. A minority of CVID patients (5%-10%) have very low B-cell counts (<1% of peripheral blood leukocytes), while another subset (5%-10%) exhibit noncaseating, sarcoid-like granulomas in different organs and also tend to develop a progressive T-cell deficiency.(1) Of all patients with CVID, 25% to 30% have increased numbers of CD8 T cells and a reduced CD4:CD8 ratio (<1). Studies have shown the clinical relevance of classifying CVID patients by assessing B-cell subsets, since changes in different B-cell subsets are associated with particular clinical phenotypes or presentations.(3,4)


The B-cell phenotyping assay can be used in the diagnosis of hyper-IgM syndromes, which are characterized by increased or normal levels of IgM with low IgG and/or IgA.(5) Patients with hyper-IgM syndromes can have 1 of 5 known genetic defects—mutations in the CD40L, CD40, AID (activation-induced cytidine deaminase), UNG (uracil DNA glycosylase), and NEMO (NF-kappa B essential modulator) genes.(5) Mutations in CD40L and NEMO are inherited in an X-linked fashion, while mutations in the other 3 genes are inherited in an autosomal recessive fashion. Patients with hyper-IgM syndromes have a defect in isotype class-switching, which leads to a decrease in class-switched memory B cells, with or without an increase in nonswitched memory B cells and IgM-only memory B cells.


In addition to its utility in the diagnosis of the above-described primary immunodeficiencies, B-cell phenotyping may be used to assess reconstitution of B-cell subsets after hematopoietic stem cell or bone marrow transplant. This test is also used to monitor B-cell-depleting therapies, such as Rituxan (Rituximab) and Zevalin (Ibritumomab tiuxetan).

Reference Values

The appropriate age-related reference values will be provided on the report.

Day(s) and Time(s) Performed

Monday through Friday

Specimens are required to be received in the laboratory on weekdays and by 4 p.m. on Friday. No weekend processing.

Analytic Time

3 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed using an analyte specific reagent. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


88185 x 7

LOINC Code Information

Test ID Test Order Name Order LOINC Value
RBCS Relative B Cell Subset Analysis % In Process


Result ID Test Result Name Result LOINC Value
BCD19 CD19+ % of total Lymphocytes 8117-4
BCD20 CD20+ % of total Lymphocytes 8119-0
BCD27 CD27+ % of CD19+ B Cells In Process
B27MD CD27+ IgM+ IgD+ % of CD19+ B Cells In Process
B27N CD27+ IgM- IgD- % of CD19+ B Cells In Process
B27M CD27+ IgM+ IgD- % of CD19+ B Cells In Process
BIGM IgM+ % of CD19+ B Cells In Process
B38MN CD38+ IgM- % of CD19+ B Cells In Process
B38MP CD38+ IgM+ % of CD19+ B Cells In Process
B21P CD21+ % of CD19+ B Cells In Process
B21N CD21- % of CD19+ B Cells In Process
RBCSI Interpretation 69052-9

NY State Approved