According to the search results, dengue fever is characterized by leucopenia, which is a decrease in the white blood cell (WBC) count. The minimum WBC count that is characteristic of dengue is not specified in the search results. However, research suggests that a total WBC count below 4000 cells/mm3 can be considered as leukocytopenia, which is a predictor of dengue. It is important to note that dengue can also cause thrombocytopenia, which is a decrease in the platelet count. The normal platelet count in the body ranges from 1.5 to 4 lacs, but it can go down to as low as 20,000 to 40,000 in the case of dengue patients. If someone suspects they have dengue, they should look out for symptoms such as high fever accompanied by at least two of the following symptoms: severe headache, pain behind the eyes, joint pain, muscle and bone pain, rash, and mild bleeding.