b/c is bun to creatinine ratio and that is indicative of kidneys-- so what was high the bun or the creatinine as bun is usually dehydration and creatinine is more critical number so did they break it out as usually they do bun, creatinine and then b/c ratio?
since the tli is normal it is not epi as they ruled that out which is good as that is another protein losing disease so now you are down to ple and lymphangiecstasia but i think your vet is right on with the lymphangiecstasia
so vet did not recommend steroids as usually that is used to treat this