Bruton Tyrosine Kinase, Protein Expression, Flow Cytometry, Blood

Casandra

Casandra Test Code MC33661Version 1 (DRAFT)

Performing Lab

Lab Mayo Clinic LabLab Test ID BTKCPT Code 88184

Bruton Tyrosine Kinase, Protein Expression, Flow Cytometry, Blood

Clinical Use

Use

This test is useful for preliminary screening of X-linked agammaglobulinemia, primarily in male patients under the age of 65 or female carriers of child-bearing age under 45. X-linked agammaglobulinemia (XLA) is a primary immunodeficiency caused by variants in the Bruton tyrosine kinase (BTK) gene. The test assesses protein expression levels and helps in determining whether further genetic analysis is warranted. It is an essential tool for the clinical evaluation of male patients with less than 1% B cells and suspected immunodeficiency. Absence of BTK protein expression provides a strong rationale for pursuing genetic sequencing.

Special Instructions

This test is not indicated for patients with hematological neoplasias receiving kinase inhibitor therapy. The test should be considered for patients with suspected monogenic primary immunodeficiency, XLA. Testing is not performed on weekends or holidays, specimens collected during off-days may be canceled if they don't meet the stability criteria. Collect and ship specimens for arrival within 24 hours of collection.

Limitations

The test is only a screening tool for BTK protein expression. Approximately 20% to 30% of patients with XLA may have normal protein expression with aberrant function, undetectable by this test but identifiable through genetic sequencing. The ability to identify female carriers depends on the specific antibodies used for flow cytometry. Genetic testing provides a more definitive diagnosis and is recommended in conjunction with clinical correlation to confirm XLA.

Test Details