The vomiting that is caused by kidney problems - is it regurg (very soon after eating I mean) or delayed? Liver disease vomiting is delayed generally speaking. Although it can be regurg too before the ALT gets too high....vomiting is difficult to diagnose I know.
Is kidney disease or early CRF vomiting generally accompanied by lack of appetite as well or can the cat be hungry, eat well and vomit due to kidneys?
As Lynn said there are many causes of vomiting and I don't know if Tiggy's vomiting pattern is typical of CRF so this is just my experience...
Tiggy hardly ever vomited food (regurg after eating). If she ate she kept it down, the problem was more getting her to eat because of the nauusea/stomach acid. Before she went on medication she would vomit clear foamy patches of 'tummy juice'. Her nausea/vomiting was always accompanied by lack of appetite, stands to reason - think how you would feel if someone was pushing plates of food under your nose whilst you felt sick
Relatively early on in the CRF I started her on antacids, vomiting virtually disappeared and appetite reappeared however towards the end if I was late with a dose she would display signs of feeling nauseous, lip smacking etc