Why would my tb test blood come back inconclusive?

It happens sometimes: Quantiferon TB blood tests look at one's white blood cells to see if they remember being in contact with TB germs. If her cells act healthily but don't react more excitedly when put into a simulated TB environment, that's a negative test. If her cells get very excited and active in a simulated TB environment, that's a positive test. Results that are "in between" are inconclusive. May retest later.