I get some mild foam, but not consistently. Probably proteinuria, which could also just be a symptom of a very high protein diet. It is strange in the link, they have No 8 - Fistula. In that case you should 'feel' air bubbles when urinating. Also I would of thought the taste/smell of the urine could get foul. For me, after doing an enema, the urine is always flat.
If anyone suspects kidney damage they should cut out all salt. Imho, everyone should stop eating any and all salt in the diet - the optimum sodium values for our physiology are found in the natural foods, not by ingesting a non-organic metal ion, which sucks the energy from our healthy cells, and drowns the unhealthy ones.
Personally I wouldn't go straight to the doctor without serious symptoms. I do not know if a long term urine/distilled Water Fast (+ supplements) would help with proteinuria caused by kidney disease, but it does cure a wide range of, often vexing, problems. Certainly terminal kidney cases have recovered on relatively short-term distilled waters fast. Armstrong and others found that the urine fast/massage/im injections created new tissue to rebuild damaged body parts, so it would likely help with a fistula as well.