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Test Code XHIM X-Linked Hyper IgM Syndrome, Blood

Reporting Name

X-Linked Hyper IgM Syndrome, B

Useful For

Screening for X-linked hyper-IgM (XL-HIGM) or CD40L deficiency, primarily in male patients younger than 10 years of age

 

Ascertaining XL-HIGM carrier status in females of child-bearing age younger than 45 years of age

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

WB Sodium Heparin


Shipping Instructions


Specimens are required to be received in the laboratory weekdays and by 4 p.m. on Friday. Draw and package specimen as close to shipping time as possible. It is recommended that specimens arrive within 24 hours of draw.

 

Samples arriving on the weekend may be canceled.



Necessary Information


Ordering physician's name and phone number are required.



Specimen Required


Container/Tube: Green top (sodium heparin)

Specimen Volume: 4 mL

Collection Instructions: 

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

2. Specimens received more than 72 hours after collection will be rejected and the assay will not be performed.

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


Specimen Minimum Volume

1.2 mL

Specimen Stability Information

Specimen Type Temperature Time
WB Sodium Heparin Ambient 72 hours

Reference Values

Present

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

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

88184-Flow cytometry, cell surface, cytoplasmic

88185 x 6-Each additional marker

LOINC Code Information

Test ID Test Order Name Order LOINC Value
XHIM X-Linked Hyper IgM Syndrome, B In Process

 

Result ID Test Result Name Result LOINC Value
82964 CD40 Ligand Expression In Process
29040 CD40muIg (Function) In Process
23901 Interpretation 69052-9

Clinical Information

CD154 (CD40 ligand: CD40L) is required for the interaction of T cells and B cells as part of the normal adaptive immune response. Activation of T cells leads to the expression of the CD40L molecule on the cell surface. CD40L binds the CD40 receptor that is always present on B cells, monocytes, and macrophages (regardless of environmental conditions). This interaction of CD40L with CD40 is important in B-cell proliferation, differentiation, and class-switch recombination (isotype class-switching).

 

Patients with X-linked hyper-IgM (XL-HIGM) syndrome have defective CD40L expression on their activated helper CD4 T cells.(1,2) This leads to defective B-cell responses and the absence of immunoglobulin class-switching. These features are typified in these patients by a profound reduction or absence of isotype class-switched memory B cells (CD19+CD27+IgM-IgD-) with low or absent secreted IgG and IgA, and normal or elevated serum IgM levels.(1,2) Due to the impairment of T-cell function and macrophage activation, XL-HIGM patients are particularly prone to opportunistic infections with Pneumocystis jiroveci, Cryptosporidium, and Toxoplasma gondii.(1)

 

To date, more than 100 unique mutations of CD40LG, the gene that encodes CD40L, have been described, affecting the intracellular, transmembrane and, more commonly, extracellular domain containing the CD40-binding region.

 

A defect in surface expression of CD40L on activated CD4 T cells can be demonstrated using an anti-CD40L antibody and flow cytometry.(3,4) Since certain CD40LG mutations can maintain surface protein expression, albeit with loss of function, it is important to also evaluate CD40L-binding capacity to eliminate the possibility of false-negative results. A soluble recombinant, chimeric receptor protein, CD40-uIg, is incorporated into the assay, which assesses CD40L function by determining receptor-binding activity. Approximately 20% of XL-HIGM patients have activated CD4 T cells with normal surface expression of CD40L, but aberrant function.(4)

 

XL-HIGM is a severe type of primary immunodeficiency that affects males, and most patients are diagnosed within a few months to the first year of life. Females are typically carriers and asymptomatic. Consequently, this test is only indicated in young males (<10 years of age) or, to identify carriers, in females of child-bearing age (<45 years).

Analytic Time

3 days

NY State Approved

No

Method Name

Flow Cytometry