Glossary, and the outside sources I trust

What do all these terms mean?

Every word that's likely to appear on a discharge sheet, a lab report or a forum thread, in one line each. Grouped by where you'll run into it rather than alphabetically, because you're usually looking at one piece of paper and not the whole vocabulary.

Words for the disease itself

Chronic kidney disease (CKD) — Permanent loss of working kidney tissue, developing slowly over months or years. The current preferred term.

Chronic renal failure (CRF) — The older name for the same thing. Renal just means kidney. Still used widely, especially in older material and by owners.

Renal insufficiency — An early stage of the same process, where function is reduced but waste isn't yet building up much in the blood.

Acute kidney injury (AKI) — Sudden kidney damage over hours to days, from a toxin, a blockage or a drop in blood supply. A different situation from CKD, and sometimes reversible. A cat can have both at once.

End-stage — Advanced disease where treatment is aimed at comfort rather than slowing progression. Usually corresponds to late IRIS stage 4.

Nephron — One microscopic filtering unit. Each kidney has hundreds of thousands, and they don't grow back once lost. This is the reason the disease doesn't reverse.

Polycystic kidney disease (PKD) — An inherited condition, mainly in Persians and related breeds, where fluid-filled cysts replace working kidney tissue. Testable genetically.

Pyelonephritis — Infection in the kidney itself. Important because cats carry it silently, it makes numbers look worse, and it's curable with antibiotics. Worth asking about when a stable cat deteriorates.

Words on the lab report

Creatinine — A waste product from normal muscle activity that healthy kidneys clear. What her IRIS stage is based on. Reads falsely high in a dehydrated cat and falsely low in a very thin one.

SDMA — Another waste product, more sensitive than creatinine, rising earlier in the disease and unaffected by muscle mass. Usually what catches the disease first.

BUN (blood urea nitrogen) — A third waste product. Easily shifted by a recent meal, dehydration or bleeding into the gut, so it's read alongside creatinine rather than alone.

Azotemia — The lab finding that waste products are building up in the blood.

Uremia — When that build-up is actually making her ill: nausea, poor appetite, lethargy, mouth ulcers, bad breath. Azotemia is the number; uremia is the cat.

Phosphorus — A mineral failing kidneys can't dump. High levels make cats feel genuinely unwell and speed the disease along. The value most worth controlling.

Potassium — Drives muscle strength. Kidney cats usually run low in the earlier and middle stages, and can run dangerously high in late stage 4.

Calcium — Interacts with phosphorus and with vitamin D. Can go either way in kidney disease, which is why calcium-based binders need monitoring.

Hematocrit / PCV — The percentage of blood made up of red cells. Falls as the disease advances, because damaged kidneys make less of the hormone that drives red cell production.

Erythropoietin — That hormone. Made by healthy kidneys, replaced by injection as darbepoetin when needed.

Total protein / albumin — Blood proteins. Low albumin can point to protein being lost through leaking kidney filters.

Words on the urine report

Urinalysis — The whole urine test: concentration, protein, blood, cells, crystals, pH.

Specific gravity (USG) — How concentrated the urine is. Healthy cats concentrate well, above roughly 1.035. Kidney cats drift toward 1.008 to 1.012, close to water.

Isosthenuria — Urine sitting at roughly the same concentration as blood plasma, around 1.008 to 1.012. Means the concentrating ability is largely gone.

UPC (urine protein to creatinine ratio) — Measures protein leaking through the kidney filters. Under 0.2 normal, 0.2 to 0.4 borderline, above 0.4 proteinuric. Frequently never run, and it changes treatment.

Proteinuria — Protein in the urine. Makes the disease progress faster and has a specific treatment.

Cystocentesis — A sterile urine sample taken with a fine needle straight into the bladder, usually ultrasound-guided. Takes seconds. The only way to get a sample reliable enough for a culture.

Culture and sensitivity — Growing any bacteria present to identify them and find which antibiotic will work.

Words about staging

IRIS — The International Renal Interest Society, a nonprofit that publishes the staging system and treatment guidelines vets follow. Their site is listed below.

Stage 1 to 4 — Severity based mainly on creatinine, measured in a well-hydrated, stable cat. A description of where she is, not a prediction.

Substaging — The other half of the stage: urine protein and blood pressure. A stage without both is an incomplete answer.

Hypertension — High blood pressure. Under 140 mmHg is normal, 160 and above is treated, 180 and above is urgent.

Words about treatment

Subcutaneous fluids (sub-Q, SQ) — Sterile fluid run under the loose skin between the shoulder blades, absorbed over a few hours.

Lactated Ringer's solution (LRS) — The fluid most commonly used for that.

Phosphate binder — A powder or paste mixed into food that traps phosphorus in the gut so it isn't absorbed.

Antiemetic — A drug that stops nausea and vomiting. Maropitant (Cerenia), ondansetron.

Appetite stimulant — A drug that makes her hungry. Mirtazapine, capromorelin (Elura). Not the same thing as an antiemetic, and the confusion between the two is the most common fixable mistake in this disease.

ACE inhibitor / ARB — Benazepril and telmisartan. Reduce protein loss through the kidney filters.

Amlodipine — The standard blood pressure tablet for cats.

Darbepoetin — Injection that replaces the missing red-cell hormone in anemic late-stage cats.

Renal diet / therapeutic diet — Prescription food with reduced phosphorus, moderately reduced high-quality protein, added omega-3s, potassium and B vitamins.

Hepatic lipidosis — A liver problem that develops when a cat eats nothing for a couple of days. The reason not eating is a phone call rather than a wait-and-see.

Ventroflexion — Holding the head and neck oddly low, chin toward the chest. Classic sign of low potassium.

The outside sources I'd actually send you to

Short list on purpose.

What I've left off, and why

Fair to be explicit about this rather than just presenting a curated list.

Facebook and forum groups. For emotional support at two in the morning, they can be genuinely valuable and I wouldn't talk anybody out of one. For medical advice, treat it as advice from a well-meaning stranger who hasn't examined your cat. Doses, drug choices and whether to start something belong with the vet who has her bloodwork in front of them. The specific pattern I'd be wary of is a group with a strong house position on a treatment, because you'll get that position rather than an assessment of your cat.

Any site that sells a kidney supplement. Not because supplements are all worthless, but because you can't get an honest evaluation of a product from the people selling it. What's worth buying is on the supplements page, and the list is short.

Anything promising to reverse, repair or regenerate kidney function. Nephrons don't grow back. A claim like that tells you what the whole site is.

AI answers and article-farm pages. They're fluent, they're often broadly right, and they're wrong in exactly the places that matter, usually by flattening a distinction. The one I see most is treating "canned is better once she has CKD" as evidence that "dry food caused it". Those are different claims with different answers, and that difference is on why did my cat get this.

If there's a term on your sheet that isn't here, it's worth asking about directly, and if it's a common one I've missed I'd genuinely like to know so I can add it.