Four numbers describe a cat's kidneys. Creatinine and SDMA show how well the kidneys filter. Urea shows how much waste is building up. Urine specific gravity shows whether the kidneys can still concentrate urine. No single value is a diagnosis, and a high result in a dehydrated cat can return to normal after fluids.
This guide follows the order of a typical lab report. Reference ranges differ between machines, so compare each value with the range printed beside it, not with figures from the internet.
Creatinine
Creatinine is a waste product of muscle. Healthy kidneys filter it out at a steady rate, so the blood level reflects filtering capacity.
It has two limits. First, it is late. Creatinine usually stays inside the normal range until about three quarters of kidney function has gone.
Second, it depends on muscle. A thin elderly cat makes little creatinine, so her result can look better than her kidneys are. A heavily muscled young male can sit near the top of the range and be healthy.
The trend matters more than one reading. A value that climbs at each yearly check, even inside the normal range, deserves a closer look.
SDMA
SDMA is a newer marker that is also cleared by filtration. It tends to rise earlier than creatinine, when roughly a quarter to 40 percent of function has been lost. Muscle mass affects it far less. That makes it useful in thin older cats.
A mildly raised SDMA with a normal creatinine is a flag, not a verdict. The usual next step is a urine test and a repeat blood test a few weeks later. If it is still raised, early kidney disease becomes likely.
Urea
Urea comes from the breakdown of protein. It appears on reports as urea or BUN. The kidneys clear it, but several other things move it. A high-protein meal before the sample raises it. So do dehydration and bleeding in the gut. Liver disease and a very low-protein diet lower it.
Urea is read alongside creatinine, never alone. High urea with normal creatinine more often points to diet or dehydration than to the kidneys. When both are high, the cat usually feels it. Nausea, a poor appetite and bad breath track with urea.
Urine specific gravity
This is the number owners overlook, and it carries real weight. It measures how concentrated the urine is. Cats are desert animals, and healthy kidneys produce strong urine, typically above 1.035.
Failing kidneys lose this ability early. The urine becomes dilute, the cat drinks more to keep up, and the litter clumps grow larger. A blood result cannot be interpreted properly without it.
| Blood values | Urine | Most likely meaning |
|---|---|---|
| High creatinine and urea | Concentrated | Dehydration or poor blood flow to the kidneys. Often reversible |
| High creatinine and urea | Dilute | The kidneys themselves are not coping |
| Normal creatinine, raised SDMA | Borderline or dilute | Possible early kidney disease. Repeat and monitor |
| All normal | Concentrated | Kidneys working well today |
The urine sample also gets a protein check. Protein leaking into the urine speeds up kidney damage and changes the treatment plan.
The other lines on the report
- Phosphate. Rises as kidney function falls. Control of phosphate is a main aim of kidney diets.
- Potassium. Often runs low in cats with kidney disease and causes weakness.
- Red cell count. The kidneys make the hormone that drives red cell production, so long-standing disease causes anaemia.
- Blood pressure. Not on the blood report, but measured at the same visit. High pressure damages the eyes and the kidneys further.
Staging
Vets worldwide use a four-stage system from the International Renal Interest Society. Stage 1 is the mildest and stage 4 the most severe. The stage is set from creatinine and SDMA in a hydrated, stable cat, on at least two samples. Blood pressure and urine protein then add sub-stages.
Staging is not done on the day a cat arrives sick and dry. Values taken in a crisis overstate the stage. Our page on chronic kidney disease in cats describes what each stage means for diet, rechecks and outlook.
Summer dehydration and misleading results
From June to September, a cat in Dubai can become dehydrated without leaving the flat. The air conditioning fails for an afternoon. A cat is shut in a sunny room. She eats only dry food and the fountain runs empty. Vomiting or diarrhoea on top of that does the rest.
Dehydration reduces blood flow to the kidneys, and creatinine and urea rise. The clue is concentrated urine and a raised red cell percentage. After fluids, the values fall back within a day or two. If they stay high once the cat is hydrated, the kidneys are involved.
For a routine yearly screen, bring your cat in a cooled car after a normal night with water available. Ask whether to fast her. A urine sample collected at the same visit makes the blood result far more useful.
Persians, British Shorthairs and polycystic kidneys
Polycystic kidney disease is inherited. It is best documented in Persians and Exotic Shorthairs, and it occurs in British Shorthairs and other breeds with Persian ancestry. Those breeds are everywhere in Dubai, and many come from lines that were never screened.
Affected cats are born with tiny fluid-filled cysts in both kidneys. The cysts enlarge slowly and crowd out working tissue. Blood values often stay normal until middle age, commonly around seven.
Blood tests therefore find PKD late. An ultrasound scan of the kidneys can show cysts from about 10 months of age. A genetic cheek swab test also exists for the known Persian mutation. If you own one of these breeds, one scan in early adulthood tells you whether to watch kidney values closely.
What to bring and what to ask
- Any earlier blood reports, including those from another country. A trend needs at least two points.
- A list of food, treats, supplements and medicines.
- Your own notes on water intake, litter clump size, appetite and weight.
Ask which values are outside the range, whether she was dehydrated on the day, what the urine showed, and when to repeat the test. Blood and urine are run in our in-house laboratory, so these answers usually come during the same visit.
When to call
Book a consultation within the week if your cat is drinking or urinating more, losing weight, or eating less than usual.
Call 055 620 4085 the same day if she has stopped eating for 24 hours, is vomiting repeatedly, seems weak, or is passing no urine. Kidney values can climb fast in a cat that is not drinking. The phone is answered 24 hours, and the clinic is open 8 AM to 12 AM every day.