yes it is mandatory to undergo medical test if your wife's gonna stay here for more than a month. You can go in Medical COmmission, go there as early as 7am to avoid long queue. BRing her passport, visa, and also your copy of passport/QID. She will have to pay 100qr, provide her with atm debit because they don't accept cash. Results will be available as early as the next day or as long as a week. You can get the result online, check it everyday so you won't miss it. Then you can go and proceed with visa extension. As to my case, I didn't get the result anymore, because since Qatar has its database, the result of medical exam is automatically entered in immigtation's database too. Therefore, when you get there and they checked your visa number for extension, they will see if you have done the medical exam, and its results. :) Good luck!