Can Rashes And Increased Platelet Count Be The Cause Of Dengue?

I have a 7 year old son and have rashes all over his body. His fever started 4 days ago but since last night (after 3 days) his body temp. is always at 36.5 degrees Celcius up to now. I have his blood examine today and his platelet count is 172 per liter. Is that already a dengue symptoms, or is his symptoms are now going to be ok? I will again have his blood examine tomorrow to see if the platelet count is going down.