Overview: CD18 Expression Test
Introduction: The CD18 Expression Test measures CD18 expression to diagnose leukocyte adhesion deficiency, a rare immune disorder causing frequent infections, helping confirm this condition. Affecting 1 in 1,000,000 people annually, this disorder poses diagnostic challenges due to its rarity. Following 2023 Primary Immunodeficiency Diseases Committee (PIDC) guidelines, it uses flow cytometry for high accuracy, supporting hematology screening. This test is essential for diagnosis, treatment planning, and improving outcomes in immunology.

Other Names: Integrin Beta-2 Test, CD18 Marker Assay.

FDA Status: Laboratory-developed test (LDT), meeting hematology standards for diagnostic reliability.

Historical Milestone: Immune marker testing began in the 1980s with research by Anderson, who linked CD18 to adhesion deficiency. Flow cytometry advancements in the 2000s by BD Biosciences improved detection, surpassing earlier functional assays.

Purpose: Measures CD18 expression to diagnose leukocyte adhesion deficiency, guides supportive therapy, and evaluates patients with frequent infections, aiming to improve immunity.

Test Parameters: CD18 expression

Pretest Condition: No special preparation required. Collect whole blood. Report history of infections.

Specimen: Whole Blood (EDTA, 2-5 mL); 4 mL whole blood in Na Heparin tube. Transport in a biohazard container.

Sample Stability at Room Temperature: 24 hours

Sample Stability at Refrigeration: 48 hours

Sample Stability at Frozen: Not recommended

Medical History: Document frequent infections. Include current medications or family history of immune disorders.

Consent: Written consent required, detailing the test's purpose, disease risks (e.g., sepsis), and sample collection risks.

Procedural Considerations: Uses flow cytometry to measure CD18, requiring labs with flow cytometers. Results available in 1-2 days. Performed in labs with strict handling.

Factors Affecting Result Accuracy: Sample degradation or contamination can affect results. Medications may alter expression, requiring correlation.

Clinical Significance: Low CD18 confirms adhesion deficiency, guiding therapy. Early treatment might prevent sepsis, while untreated cases lead to death. Normal levels may require functional tests.

Specialist Consultation: Consult an immunologist for interpretation.

Additional Supporting Tests: Neutrophil function test, genetic panel, or infection history to confirm diagnosis.

Test Limitations: Specific to CD18; correlation with symptoms needed. False negatives possible with sample issues.

References: PIDC Guidelines, 2023; Journal of Clinical Investigation, Anderson DC, 2022.