Tuberculin Skin  Test 

T-SPOT.TB 

False Positives

• BCG vaccination
• Environmental mycobacterium

T-SPOT.TB is very specific:

• Specificity approaching 100%
• Not affected by BCG vaccination
• Does not cross-react with common environmental mycobacterium

False Negatives

• Skin reaction is a mixed immune response (problem in immunosuppressed patients)
• Often negative in active disease (75-90% sensitivity, lower in immunosuppressed).

T-SPOT.TB is very sensitive:

• Sensitivity ~95%
• Identifies infected subjects missed by TST
• Immunosuppression has little effect
• Performance maintained in infants
• High sensitivity in active TB, including extrapulmonary TB