Harrison's blood tests came back normal. This doctor (the one who interpreted the tests) said both the itching and the spots are just rashes. He (Harrison) is still itchy but otherwise seems to be more lively. We'll see what today brings.
[Addendum: I forgot to include Harrison's reaction to the blood test. He did not seem relieved at all, as he did not appear to be worried in the first place. However, upon hearing that the tests were all good, he said "Good. Now can I get my blood back?"
I told him he would just have to make some more.]