Dengue Diagnosis and Prognosis: The diagnosis of dengue is usually made clinically. To confirm the diagnosis doctor will do blood tests to identify the presence of dengue virus. The dengue virus can affect the platelet production/count in some patients. The virus affects the body's ability to form new platelets and the number of platelets decrease. The prognosis of dengue fever is quite good. Most patients with dengue fever recover without any sequel. Read articles on how is dengue diagnosed and about prognosis of dengue.