A blood glucose reading under 60 mg/dL is hypoglycemia, and it runs on a 15-minute clock: treat what you see, retest in 15 minutes, and be at a clinic within 2 hours if the number will not hold. On the way, do not syringe sugar water into the mouth of a cat that cannot swallow, do not give a second insulin dose to fix a rebound, and do not wait for the next scheduled meal.
One number sets the rule: 60 mg/dL
A healthy cat sits around 70 to 150 mg/dL. Below 60 is the treatment line for a cat on insulin. Below 50 most cats show signs, and below 40 the brain runs out of fuel and seizures start. Home meters read within 10 to 15 percent of a lab value, so a 58 can be a 50 or a 66 in the clinic; treat the cat, not the decimal.
A kitten under 12 weeks has small glycogen stores and can drop under 60 after 8 to 12 hours without food, so its fasting window stays under 6 hours.
Three groups of signs, in the order they appear
- Nerve and muscle: a wobbly walk, hind legs that cross or drag, a head held low, fine muscle twitching, and in the last stage a stiff jaw or a full seizure. These show at roughly 50 mg/dL and below.
- Behavior: staring at a wall, slow reactions, hiding, yowling at night, or not recognizing your voice, often 30 to 60 minutes before the wobble.
- Whole body: drooling, dilated pupils, a temperature under 37.5 C, pale gums, and a heart over 220 beats per minute. Cats do not sweat, so cool ears stand in for that sign.
Any 1 group plus a meter reading is enough. Do not wait for all 3: the gap between the first wobble and a seizure is often 15 to 30 minutes.
Test at home in 4 steps
Warm the ear for 10 seconds between your palms to bring blood up. Use the outer edge of the ear, away from the main vein, with a 26 to 28 gauge lancet; a 0.3 to 1 microliter drop is enough for most meters, and the strip reads in 5 seconds. Hold the ear flat, not pinched, and let the drop form. Log the number, time, and last meal; 6 readings a day for 3 days shows a vet the pattern, and 1 reading is a snapshot.
Human meters are fine for trending, with 1 caveat: low readings tend to run 5 to 15 mg/dL off. If your meter says 45 and the cat looks fine, retest.
What goes on the gums, and what never goes in the mouth
A conscious cat that can swallow gets a thin smear of glucose syrup or honey inside the lip, where it absorbs through the lining; how much is your vet's call for your cat's weight, so ask before 3 a.m. A cat that is seizing, limp, or cannot swallow gets nothing by mouth, because 1 to 2 mL going down the wrong way causes aspiration pneumonia, which is a 3 to 5 day hospital stay on top of the low sugar.
Injectable 50 percent dextrose and glucagon come only on a veterinary prescription, and are clinic drugs: the dose depends on weight, on the reading, and on whether the cat is on a drip. Never adjust an insulin dose on your own after 1 low reading, and never switch between U-40 and U-100 syringes: the same volume delivers 2.5 times the insulin, which is one of the most common causes of a 30 mg/dL crash.
The 15-minute recheck, and what the second number means
| Reading | What it means | Act now | Recheck |
|---|---|---|---|
| Above 250 mg/dL | High, no extra insulin without the vet | Water, note the time, call | 2 to 4 h |
| 80 to 150 mg/dL | Target range for a treated cat | Feed the normal meal | 6 to 8 h |
| 60 to 79 mg/dL | Low normal, heading down | Small meal, no insulin | 15 min |
| 40 to 59 mg/dL | Clinical hypoglycemia | Syrup on gums, call the vet | 15 min |
| Under 40 mg/dL | Seizure territory | Drive now, keep the cat warm | On arrival |
Two readings 15 minutes apart both under 60, or a number that falls after treatment, means the clinic, not the kitchen. A reading past 80 that holds for 2 checks buys a phone call instead of a drive.
Why the clinic wants 2 hours, not 2 days
In the clinic the first moves are a measured glucose, then intravenous dextrose on a veterinary prescription, then a 2 to 6 hour glucose curve to see whether the cat rebounds and crashes again. A single low reading that corrects in 10 minutes is often an insulin dose that is 0.5 to 1 unit too high for that day's food intake; a cat that crashes twice in 24 hours needs the whole insulin plan rebuilt, plus blood work for infection, kidney disease, and liver disease.
Cost splits the same way: an urgent visit with a curve runs 150 to 350 USD, while a seizure needing oxygen, a drip, and 24 to 48 hours in hospital runs 900 to 2,000 USD.
Five causes that repeat
- Insulin given while the cat was not eating, or a meal refused 30 to 60 minutes after the shot.
- A syringe mix-up: U-40 insulin drawn in a U-100 syringe, or the reverse, which is a 2.5 times error in either direction.
- Two people in the house both giving the morning dose, which doubles it.
- Vomiting for 12 hours or more on top of a normal dose; if a plant is the suspect, run the name through a toxin list first.
- Diabetic remission: 20 to 30 percent of cats eventually need less insulin or none, and the first sign is a low reading at the usual dose.
Timeline at 0, 15 minutes, 2, 6, and 24 hours
- 0 minutes: meter reading, gum smear if the cat can swallow, cat on a warm towel, phone the clinic.
- 15 minutes: recheck. Under 60 again means drive; 80 or above means feed a small meal and recheck at 30 minutes.
- 2 hours: at the clinic, glucose curve started, insulin plan reviewed, no dose given at home that day.
- 6 hours: next meal on schedule, half the usual insulin only if the vet says so; a cat that will not eat gets no shot.
- 24 hours: 4 to 6 readings logged, dose decision made on the pattern, not on the single worst number.
A cat that seizes, goes limp, or cannot be roused is past the home stage: keep it warm, keep the airway clear, and drive, because a seizure from low glucose can leave damage in 15 to 30 minutes. If the seizure repeats within 24 hours, that is a cluster, handled as a seizure cluster emergency, and the glucose reading goes with you on paper.
Frequently asked
My cat read 58 mg/dL but seems fine. Do I still treat?
Yes, a reading under 60 is the treatment line for a cat on insulin, whatever the cat looks like. Give a small meal, skip that insulin dose, and recheck in 15 minutes; 2 readings still under 60 after treatment mean the clinic, not the kitchen. Home meters run 10 to 15 percent off, so 58 could be 50, and cats hide the signs until roughly 50 mg/dL.
Can I squirt sugar water into my cat's mouth during a seizure?
No. A seizing or limp cat cannot swallow, and 1 to 2 mL going down the wrong way causes aspiration pneumonia, which turns a 15 minute event into a 3 to 5 day hospital stay. Keep the cat warm, clear the area, note the time, and drive. A conscious cat that can still swallow gets only a thin smear of syrup inside the lip, and the amount is set by your vet.
Why recheck at 15 minutes instead of waiting for the next meal?
Glucose after a gum smear or a small meal turns within 10 to 15 minutes, so the recheck is the earliest honest signal. A number that rises past 80 and holds for 2 checks means a phone call; a number under 60 twice, or one that falls after treatment, means intravenous dextrose on a veterinary prescription and a 2 to 6 hour curve in the clinic.