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HelpTest Code BTK Bruton Tyrosine Kinase, Protein Expression, Flow Cytometry, Blood
Reporting Name
Btk Protein Flow, BUseful For
Preliminary screening for X-linked agammaglobulinemia, primarily in male patients (<65 years) or female carriers (child-bearing age: <45 years)
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Whole Blood EDTAOrdering Guidance
Bruton tyrosine kinase (BTK) protein and genetic tests are not meant for patients with hematological neoplasias on kinase inhibitor therapy, including but not restricted to the selective BTK inhibitor, ibrutinib. This test is only meant for the assessment of patients with a suspected monogenic primary immunodeficiency, X-linked agammaglobulinemia, caused by germline variants in the Bruton tyrosine kinase gene.
The preferred test for confirming a diagnosis of X-linked agammaglobulinemia in male patients and identifying female carriers is BTKSG / Bruton Tyrosine Kinase, BTK Full Gene Analysis, Varies.
In families where a BTK variant has already been identified, order FMTT / Familial Variant, Targeted Testing, Varies.
Shipping Instructions
Testing is performed Monday through Friday. Specimens not received by 4 p.m. (CST) on Friday may be canceled.
Samples arriving on the weekend and observed holidays may be canceled.
Collect and package specimen as close to shipping time as possible.
It is recommended that specimens arrive within 24 hours of collection.
Necessary Information
Ordering healthcare professional name and phone number are required.
Specimen Required
Container/Tube: Lavender top (EDTA)
Specimen Volume: 4 mL
Collection Instructions: Send whole blood specimen in original tube. Do not aliquot.
Specimen Minimum Volume
2 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole Blood EDTA | Ambient | 48 hours | PURPLE OR PINK TOP/EDTA |
Reference Values
Present
Day(s) Performed
Monday through Friday
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 US Food and Drug Administration.CPT Code Information
88184
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| BTK | Btk Protein Flow, B | 75708-8 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 89011 | Btk Protein Flow, B | 75708-8 |
Interpretation
Results are reported as Bruton tyrosine kinase (BTK) protein expression present (normal) or absent (abnormal) in monocytes and B cells if present. Additionally, mosaic BTK expression (indicative of a carrier) and reduced BTK expression (consistent with partial BTK protein deficiency) are reported when present and correlated with a healthy experimental control.
BTK genotyping (BTKSG / Bruton Tyrosine Kinase, BTK Full Gene Analysis, Varies or FMTT / Familial Variant, Targeted Testing, Varies) should be performed in the following situations:
-To confirm any abnormal flow cytometry result
-In the rare patient with the clinical features of X-linked agammaglobulinemia, but normal BTK protein expression
-In mothers of patients who do not show the classic carrier pattern of bimodal protein expression (to determine if there is maternal germinal mosaicism or skewed altered X-chromosome inactivation), or there is dominant expression of the normal protein in the presence of one copy of a genetic variant.
Clinical Reference
1. Kanegane H, Futatani T, Wang Y, et al. Clinical and mutational characteristics of X-linked agammaglobulinemia and its carrier identified by flow cytometric assessment combined with genetic analysis. J Allergy Clin Immunol. 2001;108(6):1012-1020. doi:10.1067/mai.2001.120133
2. Kanegane H, Tsukada S, Iwata T, et al. Detection of Bruton's tyrosine kinase mutations in hypogammaglobulinemic males registered as common variable immunodeficiency (CVID) in the Japanese Immunodeficiency Registry. Clin Exp Immunol. 2000;120(3):512-517. doi:10.1046/j.1365-2249.2000.01244.x
3. Stewart DM, Tian L, Nelson DL. A case of X-linked agammaglobulinemia diagnosed in adulthood. Clin Immunol. 2001;99(1):94-99. doi:10.1006/clim.2001.5024
4. Futatani T, Miyawaki T, Tsukada S, et al. Deficient expression of Bruton's tyrosine kinase in monocytes from X-linked agammaglobulinemia as evaluated by a flow cytometric analysis and its clinical application to carrier detection. Blood. 1998;91(2):595-602
5. Kraft MT, Pyle R, Dong X, et al. Identification of 22 novel BTK gene variants in B cell deficiency with hypogammaglobulinemia. Clin Immunol. 2021;229:108788. doi:10.1016/j.clim.2021.108788
6. Chear CT, Ripen AM, Mohamed SAS, Dhaliwal JS. A novel BTK gene mutation creates a de-novo splice site in an X-linked agammaglobulinemia patient. Gene. 2015;560(2):245-248. doi:10.1016/j.gene.2015.02.019
Report Available
3 to 4 daysMethod Name
Flow Cytometry