Table 4. Median and mean IFN-γ measurements for QuantiFERON-TB Gold In-Tube tests performed on the same subjects in three labs.

Source	n	Nil		TB		TB Response
		Median	Mean	Median	Mean	Median	Mean
Lab1 (original) unstratified	97	0.07	0.10	0.27	4.11	0.15	4.01
Lab2 (original) unstratified	97	0.06	0.09	0.24	3.88	0.19	3.79
Lab3 (original) unstratified	97	0.07	0.11	0.40	5.92	0.26	5.81
Lab1 (reconciled)
Unstratified *	91	0.07	0.09	0.18	3.11	0.08	3.01
Concordant Positive†	35	0.07	0.11	3.93	7.85	3.31	7.74
Concordant Negative§	49	0.07	0.08	0.08	0.10	0.01	0.02
Lab2 (reconciled)
Unstratified *	91	0.06	0.09	0.16	2.91	0.09	2.83
Concordant Positive†	35	0.07	0.11	4.47	7.37	4.23	7.26
Concordant Negative§	49	0.06	0.07	0.08	0.09	0.01	0.02
Lab3 (reconciled)
Unstratified *	91	0.07	0.11	0.32	2.94	0.18	2.33
Concordant Positive†	35	0.07	0.12	3.72	6.04	3.25	5.91
Concordant Negative§	49	0.07	0.10	0.11	0.14	0.02	0.05

Nil = IFN-γ concentrations (IU/mL) in plasma from the Nil tube of the QuantiFERON-TB Gold In-Tube test (QFT-GIT); TB = IFN-γ concentrations (IU/mL) in plasma from the TB tube of QFT-GIT; TB Response = TB minus Nil.

^*Includes 7 subjects with discordant QFT-GIT interpretations.

^†Concordant positive among results from all 3 labs.

^§Concordant negative among results from all 3 labs.