Glucose and fructosamine: a snapshot and an average
Match the time scale of each test with symptoms and urine findings instead of diagnosing from one high result.
Prepared by TengRip · Guide updated：2026-10-25
Not veterinarian-reviewed; a report-reading guide, not a diagnosis.
Read these findings together
GLU measures the sampling moment; FRU reflects a period of blood glucose. An average does not show daily peaks and lows. Neither result alone is a diagnosis or a reason to change insulin yourself.
This site does not list fixed normal values: reference ranges differ by analyzer and method, so always use the range printed on your report.
Work through your report
- Note food, stress and medicines before sampling.
- Bring changes in drinking, urination, appetite and weight, plus urine findings.
- Keep single GLU values, repeated monitoring and FRU distinct.
| Test | Clues and limits | Related information |
|---|---|---|
| GLU | Blood glucose at sampling; food, stress and medicines can affect it. | Symptoms, repeated glucose, urine glucose/ketones and fructosamine. |
| FRU | Reflects glucose over a period; an average cannot show daily peaks and lows. | Glucose records, symptoms, urine findings, protein and thyroid information. |
Blood Glucose (GLU)
The level of sugar in the blood. Glucose can rise temporarily when a cat is stressed at the clinic, so a single high value is not necessarily diabetes and often needs other tests to confirm.
What it measures
Glucose is the body's main energy source. It comes from food, is stored and made by the liver, and is regulated by insulin. A persistently high glucose is the main feature of diabetes, but glucose is also easily affected by short-term factors such as meals and stress.
What a high value may mean
Possible causes include a recent meal; stress or excitement (an adrenaline-driven rise usually lasts 4 to 6 hours, while a rise driven by stress hormones can last several days); diabetes; other hormone diseases; and some drugs. Cats are especially prone to stress hyperglycemia at the vet and may even show temporary glucose in the urine, so a single high blood or urine glucose cannot confirm diabetes.
What a low value may mean
Possible causes include a sample that was not processed in time (blood cells keep using up glucose, causing a false low); an insulin dosing problem; xylitol eaten by a dog; a long time without food; severe infection; poor liver function; and some tumors (such as insulinoma in dogs).
Usually read together with
A urine test (glucose and ketones), fructosamine, and liver values. Fructosamine reflects average glucose over a period of time and helps tell true diabetes from short-term stress; however, research shows that even with very high glucose, it takes about 3 days for fructosamine to rise in cats.
When to follow up
If your cat drinks more, urinates more, and loses weight despite eating a lot, along with high glucose, follow your vet's plan for confirmation tests such as fructosamine or a urine test. If a cat on insulin has a low glucose reading, contact your vet directly and do not change the dose on your own.
Section sources
Fructosamine (FRU)
Helps assess sustained versus brief stress-related high glucose; not measured in the supplied extracts.
Related clinical questions
Reflects glucose over time rather than at collection, supporting diabetes assessment and follow-up.
Why this marker matters
Roughly represents the past two weeks and is less affected by brief stress, but hides daily highs and lows.
Interpretation limits
Low protein or hyperthyroidism may affect interpretation. A normal result does not replace a full assessment.
Tests to read alongside it
Symptoms, repeat glucose or curves, urine glucose and indicated ketones, alongside protein and thyroid findings.
Questions at follow-up
Ask whether FRU adds useful information and how to monitor. Never change insulin doses from an average alone.
Section sources
Questions for the visit
- What distinguishes transient from persistent elevation?
- Do protein or thyroid findings affect FRU interpretation?
- What monitoring and contact plan should we follow?
Compare anonymous reports
Practise with real reports →
Three clinics and three cats: how kidney markers, glucose, pancreatic lipase and blood counts inform clinical questions.
Related app: Chronlo (Google Play · App Store)
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This site is for general reference only and is not a substitute for veterinary diagnosis. If your cat shows unusual signs, please see a vet promptly.