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TABLE 1

Comparison of the TST and IGRAs

CharacteristicTSTIGRA
Antigens used Many; PPD 3 (QFT) or 2 (T-SPOT) 
Sample Intradermal injection Blood draw 
Patient visits required 
Distinguish between LTBI and TB disease No No 
Cross-reactivity with BCG Yes No 
Cross-reactivity with NTM Yes Only rare speciesa 
Differing positive values by risk Yes (5-10-15) No 
Causes boosting Yes No 
Subject to boosting by previous TST Yes Possible 
Durability over time (stays positive with or without treatment) Yes Unknown 
Difficulties with test reproducibility Yes Yes 
Relative cost Lower Higher 
Location of need for trained staff “Bedside” Laboratory 
Estimated specificity in BCG-unvaccinated children 95% to 100% 90% to 95% 
Estimated specificity in BCG-vaccinated children 49% to 65% 89% to 100% 
Estimated sensitivity (confirmed TB disease) 75% to 85% 80% to 85% 
Estimated sensitivity (clinical TB disease) 50% to 70% 60% to 80% 
CharacteristicTSTIGRA
Antigens used Many; PPD 3 (QFT) or 2 (T-SPOT) 
Sample Intradermal injection Blood draw 
Patient visits required 
Distinguish between LTBI and TB disease No No 
Cross-reactivity with BCG Yes No 
Cross-reactivity with NTM Yes Only rare speciesa 
Differing positive values by risk Yes (5-10-15) No 
Causes boosting Yes No 
Subject to boosting by previous TST Yes Possible 
Durability over time (stays positive with or without treatment) Yes Unknown 
Difficulties with test reproducibility Yes Yes 
Relative cost Lower Higher 
Location of need for trained staff “Bedside” Laboratory 
Estimated specificity in BCG-unvaccinated children 95% to 100% 90% to 95% 
Estimated specificity in BCG-vaccinated children 49% to 65% 89% to 100% 
Estimated sensitivity (confirmed TB disease) 75% to 85% 80% to 85% 
Estimated sensitivity (clinical TB disease) 50% to 70% 60% to 80% 
a

Mmarinum, Mkansasii, Mszulgai, and Mflavescens.

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