Hello doctor, my one year old baby has a very high platelet count 1183000/mm3. i inform you that he is taking antibiotics for two weeks following an infection in his "arthritis" shoulder?

Your baby probably has reactive thrombocytosis (high platelet count due to infection), especially if baby had a normal platelet count number previously and repeat number will be lower after infection resolves.

A follow up imaging study, CBC, Differential and Platelet count should be considered. A septic joint will require a few weeks of antibiotic treatment. The platelet count should decline along with inflammatory markers.