Your X ray
must have shown a spot with possibility of Tuberculosis it may be a spot of childhood or sometimes it may reactivate and can cause disease. So sputum samples for Acid Fast Bacilli is tested to rule out active Tuberculosis
. Do you have fever
,Loss of weight or cough and sweating more so in the evening if no . You say your blood test
are normal then threre is more possibility of sputun should come negative and you shold pass the medical test.
Best of luck