Blood Glucose Curves 101: Reading Them at Home
A string of numbers on a page doesn’t mean much until you know what a “good” curve actually looks like. Here’s how to read one the way your vet does.
Never adjust an insulin dose yourself based on a curve — bring the data to your vet for interpretation. This is about understanding what you’re looking at, not making treatment decisions solo.
What a Glucose Curve Actually Shows
A blood glucose curve is a series of readings taken across a full dosing interval — typically 10-12 hours for twice-daily insulin — to see how high glucose rises, how low it drops, and how long the insulin keeps working. Home curves are often preferred over clinic ones because AAHA’s guidelines note that stress alone can artificially raise a dog’s glucose in a clinic setting, making insulin look less effective than it actually is.
Two Ways to Test
| Traditional glucometer | CGM (FreeStyle Libre-type sensor) | |
|---|---|---|
| How it works | A drop of blood from the ear, lip, or paw pad, checked every 1-2 hours | A sensor reads tissue glucose continuously, scanned as needed |
| Best for | Precise nadir values, confirming a CGM reading | Multi-day trends, catching lows between scheduled checks |
| Downside | Repeated pricks, only a handful of data points | Not specifically calibrated for veterinary use; sensor placement and adhesion can affect accuracy |
Neither is strictly better — many owners use a glucometer to confirm a concerning CGM reading before making any decisions.
The Numbers That Actually Matter
| Measurement | Target | What it means |
|---|---|---|
| Nadir (lowest point) | 80-150 mg/dL | Below 80 signals hypoglycemia risk; consistently above 150 may mean the dose or duration needs adjusting |
| Highest point | Close to 200 mg/dL | Higher readings suggest the dose or duration isn’t quite covering the full interval |
| Daily range | Roughly 100-250 mg/dL | Where a well-controlled dog spends most of the day, per AAHA guidance |
The Pattern That Fools a Lot of Owners: The Somogyi Effect
If the dose is actually too high, glucose can crash low enough to trigger a rebound — the body dumps stress hormones that push glucose back up, sometimes dramatically. Without seeing the nadir, that rebound can look exactly like “not enough insulin,” when the real fix is to lower the dose, not raise it. This is exactly why the full curve matters more than any single reading.
Recognizing Hypoglycemia During a Curve
If signs appear during a curve or at any other time, our hypoglycemia emergency guide covers exactly what to do based on how responsive your dog is.
If your dog is conscious and can swallow safely, rubbing a small amount of Karo syrup or honey on the gums and offering a meal can help — then call your vet regardless of how quickly they seem to recover. If they’re unconscious or seizuring, get to a vet immediately rather than trying to manage it at home.
Logging and Sharing Data With Your Vet
- Record Time, reading, and device used for every check.
- Note Insulin dose and timing, meal details, and anything unusual — vomiting, missed meals, extra activity.
- Graph it A simple line chart with insulin and meal times marked makes the nadir and duration obvious at a glance.
- Share promptly Send the data to your vet rather than trying to interpret and act on it yourself.
FAQ
How often should I run a full curve?
Your vet will set the schedule based on your dog’s stability — often more frequently right after starting insulin or changing doses, then spacing out once things are stable. Follow their specific plan.
Is CGM accurate enough to trust for dogs?
Studies generally show CGM readings fall within a clinically acceptable range for dogs, though it’s not specifically calibrated for veterinary use. Confirming a concerning reading with a glucometer before acting is a reasonable habit.
My dog’s numbers look high — should I increase the insulin dose myself?
No — a high reading without knowing the nadir could actually mean the dose is too high, not too low (the Somogyi effect). Always bring the full curve to your vet rather than adjusting on your own.
The Bottom Line
A glucose curve is really just three numbers that matter — the nadir, the peak, and how long insulin lasted — plus the pattern between them. The single habit that prevents the most common mistake: never react to one high number without knowing what the nadir looked like first.
This article is for informational purposes only and isn’t a substitute for veterinary diagnosis or treatment. Always have your vet interpret glucose curves and adjust insulin dosing.