Welcome to the forum CXP, sorry to hear you kitty is having kidney issues.
The percentages listed on the can are "as fed values" if you wish to compare foods & to get an accurate amount of each item (protein, phos etc) you need to "remove" the water content from the value.
Calculation goes like this:
So if you take the example of Evo 95% Chicken & Turkey
100-73.99(moisture listed)=26.01(dry matter)
To check dry matter phos level:
0.23%(as fed phos listed)/26.01(dry matter from calculation above)=0.0088*100=0.88% dry matter phos - which is under the target of 1% dm phos most vets like to see.
Kidney cats do not require low protein, but high quality protein low phos food. Removing too much protein from the cats diet makes it less palatable therefore they often refuse to eat, plus cats are carnivores they need meat protein to keep their bodies functions to the fullest.
Fish should be avoided when possible especially tuna, but fed on occasion 1-2 per month is still okay. Cats often become addicted to fish and will eat nothing else and tuna especially creates an imbalance in vit e levels.
When looking for a canned food look for quality ingredients, no fillers, actual meats ie chicken, turkey avoid anything that says "meat" meal cuz you don't know what the "meat" is, and low phos. Really read the ingredients in the food if there actual food listed in the first 6 ingredients and in the first 3 being specific meat or meal variety listed and there are not mostly chemicals it's a better quality food. Compare the ingredients in any can of Wellness to any can of the prescription foods which would you rather eat?
A listing of low phos canned can be found here however this list may not be up to date *formulas do change* and does not include Wellness Chicken 1.15% dm phos, Turkey 1.05% dm phos, Chicken & Beef 1.17% dm phos, Kitten 1.15% dm phos which are the lowest of the Wellness varieties, Nature's Variety Instinct Chicken @ 1.22% dm phos good for occasional meal, the other NV flavours are too high.
When looking at phos levels you want to convert to dry matter (meaning whats left if you remove all water) and find something as close to or lower than 1% phos dry matter.
Foods need to be compared using "dry matter amounts" instead of "as fed amounts" because there is so much difference in moisture content, therefore there is varying amounts of nutrients in different foods
It is always a good idea to add water to the canned food, this helps the cat get more fluids as healthy cats usually drink very little.
When you have an animal with compromised kidneys they should not be eating dry food, it does not add any moisture to their diet. If absolutely necessary however the majority of the diet should be canned with minimal dry. The same dry matter calculation can be used to remove the little moisture in the dry foods for comparison.
Some good quality low phos canned food choices for you:
By Nature Organics
Turkey & Turkey Liver, Chicken & Chicken Liver, Turkey & Chicken, Chicken & Mackerel, Beef & Beef Liver
Evo 95% Chicken & Turkey
Felidae Cat & Kitten
Felidae Grain Free
Merricks Before Grain 96% Beef
Merricks Before Grain 96% Turkey
Merricks Cowboy Cookout
Merricks Thanksgiving Day Dinner
Turkey, Chicken, Beef & Chicken, Beef & Salmon, Kitten, Wellness Core Chicken Turkey & Chicken Liver
Holistic Select Turkey & Barley
Holistic Select Duck & Chicken
This is a currently updated list 2010-2011 the foods are listed in order of lowest amount of dry matter phosphorus, it's up to you to decide what ingredients are acceptable, the manufactures websites are also listed to help in that regard. Tanya's Feline CRF US Canned Food Data Tables
Feel free to ask any questions