Travel in the Saada region of northern Yemen is strongly discouraged because of the risk of violent civil unrest. Travel to the eastern parts of the country (Ma'rib, Shabwah, Hadramawt) and the south (Aden, Abyan, Al-Bayda') is also inadvisable because Al-Qaeda is active in some of these areas.
Your doctor will not test for illegal drugs unless you ask him to. A CBC stands for complete blood count which has to do with your blood cells not drugs.
A complete blood count (CBC) is a laboratory test that measures several basic parameters of human blood including the red blood cell counts (erythrocytes), white blood cell counts (leukocytes) and platelets (thrombocytes).