My 10-year Old Son Had Blood On The Toilet Tissue

My 10-year old son had blood on the toilet tissue when he wiped. I thought maybe he just strained a little too hard but then he pointed out unusual markings on his thighs which looked like bleeding under the skin (petechia?). I don't know if the two are related, but I will take him to the pediatrician first thing. He doesn't seem to have any other symptoms. Can you shed any light?