I had TB 10 years ago but fully recovered. Before I came to Qatar I have done all the necessary medical check up and informed my employer regarding this. They accept it, because I am perfectly healthy, but when it comes to Qatar Medical Commission, it will be different story. To cut short, my medical status was unfit and my employer send me back to my home country. My honest opinion, if you had TB before, better don't risk leaving your current job as I think chances to work in Qatar are very slim.