Low blood and platelet count?

My father has been in the hospital for over 3 weeks. He has 2 leaking heart valves and has congestive heart failure so he has been very swollen. He is 75 and the doctors say his blood count is at 6.6 and is in need of a blood transfusion. He received a plasma or platelet transfusion a few days ago and its back down. They have done many test and ultimately said it might be from an "autoimmune" problem whatever that means. At the end they say he isn't doing well since his heart is at the end state but what else could cause your blood levels to drop so low??? They say he isn't bleeding and all test results come back ok. I should also mention that his kidneys and liver is failing as well, although they have gotten better lately.