Urea and creatinine levels in dogs and cats, units and reference ranges

Why two lab reports cannot be compared side by side

The same creatinine result is written in several ways depending on the laboratory. UK practices usually report creatinine in µmol/L and urea in mmol/L, while most of the material you will find online comes from the United States, where creatinine is given in mg/dL and urea appears as BUN. Some French laboratories print mg/L as well. There is a factor of 88.4 between mg/dL and µmol/L, and a factor of 10 between mg/L and mg/dL, so an owner comparing a British report with an American table can be out by a factor of 10 or 88 without noticing, which turns an ordinary value into an alarming one or the reverse.

The conversions themselves are fixed and easy to check:

• Creatinine, mg/dL to µmol/L: multiply by 88.4.
• Creatinine, mg/L to µmol/L: multiply by 8.84.
• In other words, 10 mg/L = 1 mg/dL = 88.4 µmol/L.

Urea, urea nitrogen and the factor of two

Urea is reported in mmol/L, in mg/dL and in some countries in g/L. American and many other English language reports also carry a parameter that resembles urea without being it: BUN, blood urea nitrogen, which is only the nitrogen inside the urea molecule rather than the whole molecule. Treating one as the other introduces an error of 2.14 times, and it is the single most common mistake made when reading a foreign report.

• Urea, mg/dL to mmol/L: multiply by 0.1665.
• Urea, g/L to mmol/L: multiply by 16.65.
• BUN, mg/dL to urea in mmol/L: multiply by 0.357.

This site always expresses creatinine in µmol/L and urea in mmol/L so that two results stay comparable from one page to the next. The Bon Poil decoder reads a report and does the conversion for you.

Typical figures, and why they are not reference ranges

As an indication only, creatinine sits at roughly 44 to 150 µmol/L in dogs and 80 to 194 µmol/L in cats, and urea at roughly 2.9 to 10 mmol/L in dogs and 6.8 to 12.1 mmol/L in cats. These spans reflect those published by university veterinary diagnostic laboratories, including Cornell, and they already differ from one laboratory to another. That is exactly why only the range printed on your own report counts: it depends on the analyser that ran the sample and on the population the laboratory used to establish it.

The species difference matters more than any single figure. Cats normally run higher than dogs for both markers. A number that would fall outside the range in a dog can be entirely normal in a cat, and that is the most common confusion among owners who keep both or who read a page written for the other species.

Why these two markers are read together and never alone

Urea rises for reasons that have nothing to do with the kidneys. A protein rich meal a few hours before the blood sample, bleeding in the gut, dehydration or hard exercise are all enough to push it up. A high urea with creatinine inside the range therefore means something quite different from a rise in both.

Creatinine depends on muscle mass, because it comes from muscle turnover. A thin, elderly, wasted animal will show a falsely reassuring creatinine, while a heavily muscled dog runs higher with nothing wrong at all. That is the reason SDMA exists, being less dependent on muscle mass, and it is also why urine specific gravity is indispensable when interpreting a creatinine: a working kidney has to concentrate urine. If the report includes a urinary creatinine, that figure is not read on its own either, it serves as the denominator of the urine protein to creatinine ratio, which corrects for dilution.

What these values cannot tell you on their own

Creatinine is a late marker: a substantial part of kidney function has to be lost before it clearly leaves the range. A creatinine within the usual values is therefore no guarantee that the kidneys are fine, and it is the combination with urea, SDMA, phosphate, urine concentration and the physical examination that points in a direction. None of these numbers, converted or not, supports a conclusion at a distance, which only the veterinary surgeon examining your animal can reach.

Questions to ask your vet

1. Which unit is my result reported in, and what is the laboratory's own range?
2. Is the value high for this species, this age and this amount of muscle?
3. Had my animal been fasted and was it properly hydrated when the sample was taken?
4. What do urine specific gravity, SDMA and phosphate show alongside these two numbers?
5. Should this be rechecked, after how long, and ideally at the same laboratory?

How do I convert dog creatinine from mg/dL to µmol/L?

Multiply the value in mg/dL by 88.4 and you have it in µmol/L, the unit used by UK laboratories. A creatinine of 1.2 mg/dL is therefore about 106 µmol/L. If the figure is in mg/L, as on some French reports, multiply by 8.84 instead, since 10 mg/L make 1 mg/dL. Always check the unit printed on that line of the report first, then compare with the range alongside it rather than with a table found online.

Is BUN the same thing as urea?

No, and the mix up is common. BUN, blood urea nitrogen, measures only the nitrogen held in the urea molecule, whereas urea refers to the whole molecule. The gap between them is 2.14 times, so reading a BUN as a urea makes a result look twice as low, and the reverse twice as high. To convert, multiply BUN in mg/dL by 0.357 to obtain urea in mmol/L.

My dog's urea is high but creatinine is normal, what does that mean?

This combination is common and does not automatically point to the kidneys. Urea rises after a protein rich meal, with dehydration, with bleeding in the gut or after hard exercise, so it is less kidney specific than creatinine. The vet will look at hydration, diet, urine concentration and possibly SDMA before interpreting anything. A recheck on a fasted, well hydrated animal often settles the question, but that decision belongs to the vet examining the animal.

Are the normal levels the same in cats as in dogs?

No, and the difference matters. Cats physiologically run higher than dogs for both creatinine and urea, so a figure that would fall outside the range in a dog can be perfectly normal in a cat. Reading a cat's result against a dog chart leads to worry for nothing, and the other way round to something being missed. Go by the range on your own report, which is set by species and by analyser.