Glucose in urine in cats and dogs

What it shows

The kidneys filter glucose out of the blood and then reabsorb almost all of it in the tubules. That reabsorption has a limit, called the renal threshold. When blood glucose climbs above it, glucose spills into urine (glucosuria). eClinPath gives the threshold as about 180–200 mg/dL (≈10–11 mmol/L) in dogs and 270–290 mg/dL (≈15–16 mmol/L) in cats, and as possibly as low as 200 mg/dL in diabetic cats. Merck gives a lower figure for cats — above 240 mg/dL — so sources differ, but in both the feline threshold is higher than the canine one.

Merck advises that whenever glucose is found in urine, blood glucose is checked.

Higher than reference — what it may be a sign of

• Diabetes mellitus — the main concern. VCA notes that large amounts usually indicate diabetes, and eClinPath calls glucosuria above 1000 mg/dL (4+ on its analyser) suspicious for it.
• Stress in cats — a frightened cat can raise its blood glucose above the renal threshold, and glucose appears in urine without diabetes (eClinPath).
• Other causes of high blood glucose — hyperadrenocorticism (Cushing’s syndrome), acromegaly, pheochromocytoma, and pancreatitis, which can cause a temporary glucosuria (eClinPath, Merck).
• Kidney tubule problems with normal blood glucose — Fanconi syndrome, primary renal glucosuria, or tubular damage from some drugs, low oxygen or infection (eClinPath, Merck). VCA notes small amounts can occur with kidney disease. In puppies under 8 weeks it can be physiological (eClinPath).
• SGLT2 inhibitors — a newer group of diabetes medicines; eClinPath notes that glucose in urine is an expected effect of them.
• False positives — hydrogen peroxide or bleach in the sample (Merck, eClinPath).

Lower than reference

Negative is the expected result. A negative strip does not rule out raised blood glucose that stays below the threshold. eClinPath and Merck also list false negatives — a lot of vitamin C in urine, ketones, cold urine, and some medicines — so in an animal with signs of diabetes the vet measures blood glucose directly rather than relying on the strip.

Look at together with

• Blood glucose — the first check after a positive strip.
• Fructosamine — reflects average blood glucose over roughly the past two weeks and is not skewed by a moment of stress (Cornell); useful in cats.
• Urine ketones — in a diabetic animal, ketones alongside glucose are a warning sign.
• Urine specific gravity — glucose raises the reading even when the animal passes a lot of urine.
• Urine sediment and culture — Cornell lists urinary tract infection among the conditions vets look for when diabetes is suspected.

Units and conversion

Urine glucose on a dipstick has no unit — it is graded negative, trace, 1+ to 4+. Each grade stands for an approximate concentration that depends on the strip: on the analyser at Cornell’s laboratory, 1+ is about 50 mg/dL, 2+ about 100, 3+ about 250 and 4+ 1000 mg/dL or more (eClinPath). A strip is a guide, not an exact number, and it says nothing precise about blood glucose at the moment of sampling. No conversion applies to a grade.

Reference range

The reference range is on your lab’s form; for urine glucose it is “negative”. Cornell describes the diagnosis of diabetes in cats as resting on persistently raised glucose in both blood and urine together with fitting clinical signs — one positive strip, especially from a cat stressed by the clinic visit, is a reason to look further, not a diagnosis. The vet decides which tests come next.

Cats and dogs

Sources

1. eClinPath (Cornell University) — Urinalysis: chemical constituents
2. Whitbread TJ. Urinalysis. Merck Veterinary Manual
3. Cornell Feline Health Center — Feline Diabetes
4. VCA Animal Hospitals — Urinalysis
5. VCA Animal Hospitals — Cushing's Disease: Testing