I just saw a research paper shared via the Winn Foundation that showed how the albumin:globulin ratio was responsible for a lot of false FIP diagnoses.What do you mean by send out tissue? So far the vets have done blood work and found high levels of globulin. They have done an abdominocentesis and looked at the fluid and its consistency and color are consistent with that of FIP. Also, all of his symptoms are pointing to FIP. What other tests can be done so I have closure and can confirm FIP?
IMHO, the best test you could do right now to be as certain as you can that this is indeed FIP (and there are other conditions that can give similar symptoms) is to send a sample of the abdominal fluid for PCR analysis. If they find the virus in that fluid then yes it most likely is FIP.
As others are saying though, the only true diagnosis is necropsy unfortunately. I went through a week of racking guilt and self-doubt when I euthanized my beloved Aziza worrying that we'd misdiagnosed her dry FIP, until the necropsy came back confirming it. In her case it was dry FIP and it can be really really hard to diagnose. There's no fluid to draw.
I'm so very sorry :-(