Table 2.

TB-IGRA detection criterion

N	P – N	T – N	Results
≤ 400	Any value	≥ 14 and ≥ $\frac{N}{4}$	Positive
	≥ 20	< 14	Negative
		≥ 14 but < $\frac{N}{4}$
	< 20	< 14	Uncertain
		≥ 14 but < $\frac{N}{4}$
≥ 400	Any value	Any value

T Testing tube (T) content value, N Negative control tube (N) content value, P (Unit: pg/ml) Positive control tube (P) content value