The short answer: High kidney values mean the blood contains more of the substances the kidneys normally filter out, usually creatinine, urea and SDMA. A single high value is not a diagnosis. Dehydration, a blockage in the urinary tract or an acute illness can produce the same numbers as chronic kidney disease. Your vet therefore reads the values together with the urine test, the blood pressure and a repeat sample once the cat is stable. If the cat turns out to have chronic kidney disease, it is divided into four stages according to IRIS, and the stage guides treatment.
What kidney values actually measure
When vets talk about kidney function they usually mean how much blood the kidneys filter per minute, the glomerular filtration rate or GFR. It does not show directly in an ordinary blood test. Instead the laboratory measures substances that leave the body only through the kidneys' filter. If the kidneys filter less, the level in the blood rises. So the values only rise once some of the filtering capacity has already been lost1.
| Value | What it is | What can affect it |
|---|---|---|
| Creatinine | A breakdown product from muscle, excreted almost only through the kidneys' filter | Muscle mass. A thin older cat can have low creatinine despite reduced kidney function |
| SDMA | A substance formed when the body's cells break down protein, filtered out by the kidneys | Less affected by muscle mass than creatinine. Methods are not standardised between laboratories |
| Urea | A waste product from the breakdown of protein | Dietary protein and other factors unrelated to the kidneys, so it is used as a second-line marker |
All three are affected by the same thing: if blood flow to the kidneys drops, or if urine cannot get out, the values rise even in a cat with healthy kidneys1. That is why it helps to have several markers to compare. IRIS, the international organisation whose staging system vets use, notes that SDMA can be raised in some situations where creatinine is not, and that two markers read together give a more reliable picture2.
A high value is not the same as kidney disease
The first question is where the increase comes from. There are three possibilities, and they often occur together1:
1. Before the kidneys (pre-renal). The cat is dehydrated, for example after several days of vomiting or poor appetite. Less blood then reaches the kidneys. Healthy kidneys respond by concentrating the urine strongly. Concentrated urine alongside high kidney values suggests the kidneys themselves are working.
2. In the kidneys (renal). The kidney tissue is damaged, acutely or chronically. The kidneys then often lose their ability to concentrate urine, and the cat urinates and drinks more. High kidney values with dilute urine is the classic pattern.
3. After the kidneys (post-renal). Urine cannot get out, for example because of a blocked urethra. This is an emergency and has nothing to do with chronic kidney disease.
Evidensia gives dehydration and bladder stones as examples of causes of high kidney values without damage to the kidneys3. Chronic kidney disease requires the change to have been present for at least three months1. That is why your vet will often want to repeat the tests.
The four IRIS stages
Chronic kidney disease is one of the most common diagnoses in older cats and progresses in most, though at very different speeds4. Once the diagnosis is made it is divided into stages. IRIS bases the stage on fasting creatinine and SDMA, preferably both, measured on at least two occasions in a cat that is stable and not dehydrated2. The limits below apply to cats.
| Stage | Creatinine, µmol/l | SDMA, µg/dl | What it usually means |
|---|---|---|---|
| 1 | under 140 | under 18 | Normal creatinine, but something else shows the kidneys are affected, such as dilute urine or protein in the urine |
| 2 | 140 to 250 | 18 to 25 | Mildly raised. Signs are usually mild or absent |
| 3 | 251 to 440 | 26 to 38 | Moderately raised. Signs from other parts of the body are common |
| 4 | over 440 | over 38 | Increasing risk of general illness and acute crises |
The lower end of stage 2 lies within many laboratories' normal range for creatinine, so a value close to the upper limit may already mean reduced function2. A persistently raised SDMA above 14 µg/dl can, according to IRIS, be used to diagnose early disease. If SDMA stays higher than the creatinine would suggest, IRIS recommends staging and treating the cat one stage higher2. The SDMA limits are based on one specific test method. Some laboratories report in other units, so ask your vet how your result should be read.
Breed matters too. Healthy Birman cats have higher SDMA and creatinine than other breeds. Up to one in five healthy Birmans can fall outside the laboratory reference range2.
Protein in the urine and blood pressure
The stage is complemented by two substages2.
Protein in the urine is measured as the urine protein to creatinine ratio, UP/C. For cats, under 0.2 counts as non-proteinuric, 0.2 to 0.4 as borderline and over 0.4 as proteinuric. Ideally two urine samples are taken at least two weeks apart.
Blood pressure is measured as systolic pressure. Under 140 mmHg counts as normal, 140 to 159 as prehypertensive, 160 to 179 as hypertensive and 180 or above as severely hypertensive, with a high risk of damage to other organs. High blood pressure can both result from reduced kidney function and make it worse. Some cats need medicine to lower it3. The classification should rest on several measurements, ideally on different visits.
Other values on the report
Phosphate. Hormones keep phosphate normal for a long time, but as the disease advances it rises1. That is one reason kidney diets have adjusted phosphorus levels.
Potassium. Around 20 to 30 percent of cats with chronic kidney disease develop low potassium, partly through losses in the urine and poorer appetite1.
Red blood cells. The kidneys produce the hormone that drives red blood cell production. As kidney function falls the cat can become anaemic, which adds to tiredness1.
Key insight: The trend says more than a single value. A creatinine that goes, say, from 120 to 150 in the same cat, measured with the same method, means more than a lone value of 150. Ask for copies of all results and keep them. The best reference value is the cat's own, taken when it was adult and healthy1.
When to see the vet
As an emergency if the cat stops eating, vomits repeatedly, is very lethargic, has pale or ulcerated gums or seems dehydrated3. A cat in stage 3 or 4 can deteriorate quickly, and an acute crisis needs treatment at the clinic. It is also an emergency if a cat strains in the litter tray without passing urine.
Within days to weeks for check-ups according to your vet's plan, or if you notice the cat drinking more, eating less or losing weight. How often depends on the stage.
What you can do yourself
Ask the right questions. Which stage is the cat in? Is it based on more than one test? What are the blood pressure and the protein ratio? When do we check again?
Follow the diet your vet suggests. Cats with kidney failure are often prescribed a special diet that is gentle on the kidneys3. Change over gradually so that the cat keeps eating.
Make drinking easy. Evidensia recommends wet food where possible, otherwise fresh water in every room or a water fountain3.
Weigh the cat every month and bring the number to check-ups.
Do not add supplements without asking. Some supplements contain phosphorus or other things that matter in kidney disease. Bring the list to your vet.
Related product
NEPHTANNU Pet Syrup. A syrup with seven herbs that have a long tradition in kidney function and fluid balance: guduchi, Boerhavia diffusa, shatavari, Bergenia ligulata, Crataeva nurvala, Hemidesmus indicus and nut grass. It is a complementary feed for older animals and replaces neither kidney diet, medicines nor check-ups. The full contents are listed, so you can show them to your vet before you start. Read more about NEPHTANNU.
Frequently asked questions
What is a normal creatinine level for a cat?
It depends on the laboratory and the cat's muscle mass. IRIS puts the stage 1 limit at under 140 µmol/l, but notes that values close to the upper reference limit can still mean reduced function2. Compare with your cat's earlier values.
Can kidney values come down again?
Yes, if the rise is caused by dehydration or an acute injury that resolves. In chronic kidney disease the damage is permanent, but the values can improve somewhat once an acute crisis or dehydration has been treated.
How long can a cat live with high kidney values?
It varies a great deal with stage, blood pressure, protein loss and how the cat responds to treatment. Evidensia writes that many cats can live a good life for several more years with the right care3. Your vet can give the best assessment for your cat.
That was the short answer. If you have a question about your own pet, email us at info@herbiovet.se. We reply within one working day.
Read on:
Sources
- Falkenö U, Selin A, Pelander L (2021). Laboratory diagnostics in suspected kidney disease in dogs and cats (Swedish). Svensk Veterinärtidning, published by SLU. PDF at SLU.
- International Renal Interest Society, IRIS Staging of CKD (modified 2026).
- Evidensia (Swedish), Chronic kidney failure in cats.
- Sparkes AH, Caney S, Chalhoub S et al. (2016). ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. Journal of Feline Medicine and Surgery, 18(3), 219 to 239. doi:10.1177/1098612X16631234