A cat that concentrates to 1.060 is using its kidney the way a desert hunter should. A cat stuck at 1.018 is losing water it cannot afford, and the first question is not which disease it has but whether the number is real. Specific gravity of 1.035 to 1.060 is normal, 1.020 to 1.035 is suspicious, and anything under 1.020 means polyuria until proven otherwise.
Pair the number with intake. A healthy cat takes in 40 to 60 mL/kg a day between bowl and food, so a 4 kg cat lands at 160 to 240 mL. When intake passes 100 mL/kg a day, the cat is polydipsic, and the urine should be dilute.
Getting a number worth reading
Specific gravity is cheap and easy to ruin. Collect midstream, before any fluid bolus, in a clean container, and read it within 30 minutes or refrigerate at 4 C for up to 24 hours. A sample taken 2 hours after 200 mL of subcutaneous fluids will read 1.015 in a cat whose own urine is 1.055, and the result means nothing. Values also differ slightly between laboratories and refractometers, so read the range printed with the sample.
Use a refractometer, not a reagent strip. A dipstick stops being useful near 1.030, which is exactly the range where the clinical question sits, and it cannot separate 1.045 from 1.060. A drop of 0.2 mL is enough on a refractometer, and the prism needs a temperature correction of about 0.001 per 5 C away from 20 C.
Two things that fake the reading
Refractometry measures refractive index, not particles, so dissolved solids inflate it. Every 1 percent of glucose adds roughly 0.004, and every 1 g/dL of protein adds about 0.003. A diabetic cat with 2 percent glycosuria can read 1.030 while its kidney is concentrating at 1.018, and a cat with marked proteinuria reads high for the same reason.
Radiographic contrast, mannitol and some plasma expanders do the same for 12 to 24 hours. If the number does not fit the cat, ask what went in the vein before blaming the kidney.
What 1.035 to 1.060 proves
Concentration is the last thing a kidney loses and the first thing worth measuring. A value of 1.035 or higher rules out central diabetes insipidus and makes primary polydipsia unlikely, because neither condition allows urine that thick. It does not rule out chronic kidney disease early: a cat can hold 1.040 with a third of its nephrons already gone, and creatinine only rises once roughly two thirds of the mass is lost.
Values between 1.020 and 1.035 are the grey zone. On dry food they are mildly concerning; on wet food at 75 to 80 percent moisture they can be normal, because a cat eating wet food takes in most of its water with dinner and never needs to concentrate hard. Read the diet before you read the number as disease.
The differential under 1.020
Five causes cover most cats: chronic kidney disease, diabetes mellitus, hyperthyroidism, pyelonephritis and post-obstructive diuresis. Diabetes usually shows glucose above 250 mg/dL and a specific gravity of 1.020 to 1.030 rather than 1.010. Hyperthyroidism raises glomerular filtration and produces polyuria in some cats, hiding behind a normal creatinine because muscle mass is falling too.
Post-obstructive diuresis is the one to watch. After a blocked tom is unblocked, urine output can run 3 to 10 mL/kg per hour for 24 to 48 hours, and potassium can drop below 3.0 mmol/L if the fluid plan does not match. A cat producing 50 mL/kg a day or more after relief needs hourly urine measurement.
One table, three columns of numbers
| Specific gravity | Urine output | Water intake | Meaning | Next step |
|---|---|---|---|---|
| 1.050-1.060 | 20-30 mL/kg/day | 40-50 mL/kg/day | Excellent concentration | Yearly check |
| 1.035-1.050 | 25-40 mL/kg/day | 45-60 mL/kg/day | Normal, diet dependent | Note the diet |
| 1.020-1.035 | 40-60 mL/kg/day | 60-100 mL/kg/day | Suspicious | SDMA, T4, glucose in 2 weeks |
| 1.012-1.020 | 60-100 mL/kg/day | 100-150 mL/kg/day | Polyuria | Urinalysis, culture, imaging |
| Under 1.012 | Over 100 mL/kg/day | Over 150 mL/kg/day | Isosthenuria | Same week workup |
The middle column is the one owners can produce at home. Collect 24 hours of litter in a pre-weighed bag, weigh it, subtract the dry litter weight and divide by 1.0 g/mL; a 4 kg cat passing more than 200 mL is at the polyuria line.
Measuring intake without guessing
Weigh the bowl. Fill a measured 300 mL, leave it 24 hours, and weigh what is left, because 1 g of water is 1 mL. Do that for 3 days and average, since a single hot day moves the number by 20 to 30 percent. Food water counts: a 400 g can at 78 percent moisture supplies about 312 mL, which is more than a 4 kg cat needs to drink in a day on wet food alone. Smell drives intake too, and the pathway runs through the vomeronasal organ, which is why a cat with a blocked nose drinks less.
Free-feeding dry food changes the math. A 4 kg cat on dry food at 9 percent moisture takes in about 10 mL from food and must drink 150 to 230 mL to reach the 40 to 60 mL/kg target. That is why dry-fed cats drink visibly and wet-fed cats often do not, and why a dry-fed cat at 1.030 deserves less alarm than a wet-fed cat at the same number.
When the numbers say go now
Call the same day for a male cat that has produced no urine for 12 hours, is crying in the litter box, or has a hard painful bladder: a urethral obstruction can kill within 24 to 36 hours once potassium passes 7 mmol/L. Also go now for a cat drinking over 150 mL/kg a day, weight loss above 10 percent in 3 months, vomiting with dilute urine, or a specific gravity fixed at 1.008 to 1.012 across 3 samples, which points to diabetes insipidus or a kidney that has stopped responding to ADH.
Never withhold water to test concentration at home. A 24 hour water deprivation is a hospital procedure with weight checks every 2 hours, and in a cat with kidney disease it can tip the animal into a crisis.
Five steps this week
- Weigh the water bowl for 3 days and average the daily mL.
- Ask the lab for specific gravity by refractometer, on a sample taken before fluids.
- Note the diet, because 75 to 80 percent moisture changes the expected number.
- Add SDMA, T4 and glucose when the value sits between 1.020 and 1.035.
- Measure 24 hour urine volume if intake passes 100 mL/kg a day.
Some breeds carry a higher risk of kidney cysts, and the breed quiz flags the Persian and related lines. Specific gravity is a 30 second test that answers a question bloodwork cannot: how hard the kidney is still working. One number plus one bowl of water, measured over 3 days, tells you whether to wait a year or book a workup this month.
Terms mentioned in this article
Frequently asked
Is 1.030 a normal urine specific gravity for a cat?
It sits at the top of the suspicious band. Values from 1.035 to 1.060 are normal for a cat, 1.020 to 1.035 are suspicious, and anything under 1.020 means polyuria. A cat on wet food at 75 to 80 percent moisture can sit near 1.030 normally, so the diet has to be read with the number.
How much water should a cat drink per day?
Total intake, including water in food, runs 40 to 60 mL/kg a day, so a 4 kg cat needs 160 to 240 mL. A dry-fed cat gets only about 10 mL from food and must drink most of it, while a 400 g can at 78 percent moisture supplies around 312 mL on its own.
Can I test concentration by taking the water away?
No. A water deprivation test is a hospital procedure with weight checks every 2 hours, and in a cat with kidney disease it can cause a crisis within a day. Measure intake with a weighed bowl for 3 days and let the veterinarian decide whether a concentration test is needed at all.