shadow on the xray result

i recently had a chest xray as part of my medical exam. The doctor found a shadow, so i was told to repeat the xray, and the same thing was found.  Now i was asked to have a sputum test.  Now I'm waiting for the result,  This is a very crucial time for me.  I want to know the rate of chance that my result will be negative.  When I did an x-ray 3 years ago, a spot was found, but when I did the sputum test, it was negative so I did not undergo any treatment.  can somebody enlighten me with my situation?  

Thanks,
louie