Why do I need an AFB test? 
You may need an AFB test if you have symptoms of active TB. These include:
Cough that lasts for three weeks or more
Coughing up blood and/or sputum
Chest pain
Fever
Fatigue
Night sweats
Unexplained weight loss 
Active TB can cause symptoms in other parts of the body besides the lungs. Symptoms vary depending on which part of the body is affected. So you may need testing if you have:
Back pain
Blood in your urine
Headache
Joint pain
Weakness
You may also need testing if you have certain risk factors. You may be at higher risk of getting TB if you:
Have been in close contact with someone who has been diagnosed with TB
Have HIV or another disease that weakens your immune system
Live or work in a place with a high rate of TB infection. These include homeless shelters, nursing homes, and prisons.
