It's usual to have the HIV and hepatitis blood tests and the TB x-ray before leaving the home country to save the employer the expense of repatriating you if you fail when they test you in Qatar. Having these tests before you leave home will not exempt you from having them again when you get to Qatar.

Before I came to Qatar my husband's employer arranged for me to be given injections for hepatitis A and B, typhoid and a combined tetanus, diphtheria and polio jab. If you're coming from the UK you might want to see what you can get on the NHS. Don't let them give you Twinrix for Hep A&B though because you can't get the follow-up jabs in Qatar.