Achord, welcome to the forum. I am so sorry that your son has gone through so much and is still going through it. I assume the hep B and C is from transfusions back before they had screening for hepatitis.
Although I have hep C and cirrhosis, I've had no personal experience with high or low blood counts. I suggest you nail down his hepatologist, if he has one, and question him directly about what concerns you. It may be difficult to get info as privacy issues come into play, since your son is an adult. You may have to ask questions in his presence, unless you have Power of Attorney.
Sorry not to be of more help, but perhaps someone else has more to offer.