I am so sorry about your cat. How long has the weight loss been going on?

Vomiting blood can be caused by numerous things, including swallowing something that might have injured the esophagus, ingesting a toxin (like d-con), liver problems, etc. I'm glad you're getting things tested at the vet's office. Please keep us posted...your situation may aid others in the future.

Best wishes to you and your cat....

Sorry that your cat is so sick....could be a number of things but if the blood work is coming back fine, I would ask the Vet if he/she could refer you to a Cat specialist. I wish I had done that originally when our then 15 year old cat started having problems. Her Vet (at the time) misdiagnosed her with Thyroid issues and when nothing worked to make her better referred her to a specialist who later determined she had intestinal cancer. I'm not saying that is what is wrong with your cat, so don't let my story frighten you what I am saying though is that when things that aren't fairly normal happen a specialist may be more able to arrive at a quicker or even more accurate diagnosis.