Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Likelihoods are at a particular context, these likelihoods change. There are childhood cancers, and bleeding is a sign of them. But recent events change the likelihood of things and having recent surgery in the region of a problem making the association with the surgery more likely. Another interesting math of medicine that is totally taken for granted is its simplicity of sets. A lab test shows a set of abnormal and diseases have sets of abnormal also. These sets do not vary as much as they could. They vary very little. So, childhood cancers would very frequently show blood count abnormalities. Things that cause overall bleeding almost always show blood count abnormalities. So, just get the twelve dollar test for blood abnormalities (complete blood count), and you get most of the possibilities. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Matt Wachsman