Glossary

All the words nobody explained at diagnosis

T1D arrives with a second language: clinic terms, device terms, and the slang other T1Ds use like you already know it. Here's the whole vocabulary in plain words. Concepts only; the numbers that fit your body come from your care team.

A1C and average glucose, translated

Type either number and the other follows, using the published ADAG formula labs use for estimated average glucose (eAG).

A1C (%)

Estimated average glucose (mg/dL)

This is an estimate for education, not a target. It comes from a population average, so a lab-measured A1C and your own CGM or meter average can both land somewhere else. Target ranges are individual and belong in a conversation with your care team.

75 terms, slang included

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15/15 rule: A common starting rule taught for treating lows: eat roughly 15 grams of fast carbs, wait about 15 minutes, check again, repeat if needed. The point is the rhythm (treat, wait, recheck) rather than the exact numbers, which your care team tunes for your body, your insulin, and your situation.
504 plan: A US legal document that spells out the accommodations a school must provide a student with T1D: glucose checks in class, snacks during tests, a plan for lows. Named for Section 504 of the Rehabilitation Act. If school pushback is a problem, this is the paper that ends the argument.

A

A1C: A blood test that reflects average glucose over the past two to three months by measuring how much glucose has attached to your red blood cells. Useful trend data for you and your care team, and a terrible report card, because it says nothing about the swings inside the average. Also written HbA1c.
AID (closed loop): Automated insulin delivery: a pump and CGM talking to each other through an algorithm that nudges insulin up and down on its own. 'Hybrid closed loop' means it still needs you for meals. It's cruise control, not a self-driving car, but it's the biggest quality-of-sleep upgrade in decades.
Arrows (trend arrows): The little arrows next to a CGM number showing where glucose is headed and how fast. A flat arrow and a diagonal arrow can turn the same number into two very different situations. Double arrows down are the universal T1D signal to stop what you're doing and deal with it.

B

Basal: The background insulin that covers you between meals and overnight, separate from food. Long-acting injections on MDI, a steady drip on a pump. When basal is right, a day without food would hold roughly steady. When it's wrong, everything else gets blamed first.
Bolus: A dose of fast-acting insulin taken for a reason: food on the way, or a high that needs correcting. The counterpart to basal. Most of the daily mental math in T1D is bolus math.
Brittle diabetes: An older label for glucose that swings hard and unpredictably. Modern care mostly retired the term, because the swings usually have findable causes, and calling a person 'brittle' helps nobody. If you hear it applied to you, it's a conversation starter with your care team, not a diagnosis to carry.

C

C-peptide: A lab test that measures how much insulin your own pancreas still makes, because c-peptide gets released alongside homegrown insulin but isn't in the injected kind. Low or absent c-peptide is part of how T1D gets confirmed.
Calibration: Entering a fingerstick reading so a CGM can true itself up. Most current sensors are factory-calibrated and don't require it, but some allow it, and older systems demanded it on a schedule. Calibrating off a rapidly changing glucose is the classic way to make a sensor worse.
Carb counting: Estimating the carbohydrates in food, because carbs are what move glucose fastest and insulin gets matched against them. Part skill, part art, part squinting at a burrito. Everyone gets better with practice and nobody is ever perfect.
Carb ratio: The personal setting that says how many grams of carbohydrate one unit of insulin covers. Set and adjusted with your care team, and often different at breakfast than at dinner, because bodies enjoy keeping things interesting. Also called an insulin-to-carb or I:C ratio.
CGM: Continuous glucose monitor: a small sensor worn on the body that reads glucose around the clock and streams it to a phone or receiver. The single biggest information upgrade in modern T1D. Also the source of every alarm you have feelings about.
Compression low: A fake low reading caused by sleeping on your CGM sensor. Pressure squeezes the tissue under it and the number nosedives while your actual glucose sits there unbothered. Classic signature: a sudden sharp low at 3 a.m. that recovers minutes after you roll over.
Control-IQ: Tandem's automated insulin delivery algorithm: reads the CGM, predicts a half hour ahead, and trims or boosts insulin to keep glucose in a target band. One of several AID systems, each with its own name and its own personality quirks.
Correction: Extra fast-acting insulin taken to bring a high back down, sized using your correction factor. The discipline is in respecting the insulin already working (see insulin on board) instead of sending reinforcements every fifteen minutes.
Correction factor: The personal setting that says how far one unit of insulin drops your glucose. Set with your care team and different for everyone, which is exactly why nobody on the internet can tell you yours. Also called an insulin sensitivity factor or ISF.

D

Dawn phenomenon: The early-morning glucose rise caused by hormones that ramp up before waking to get you ready for the day. Your liver reads the memo and releases glucose; your pancreas was supposed to answer and doesn't. Why many T1Ds run high at 7 a.m. after a perfectly flat night.
Dead in bed syndrome: The name given to rare, poorly understood overnight deaths in young people with T1D, thought to involve severe nighttime lows. It's the fear under a lot of 2 a.m. alarms, and it deserves saying plainly: it is very rare, and CGM alerts and modern AID systems exist precisely to stand guard. If this fear is loud for you, bring it to your care team; managing the fear is part of managing the disease.
Diabetes policecommunity term: Anyone who monitors your food, your numbers, or your choices without being asked. Usually love wearing a badge it wasn't issued. 'Should you be eating that?' is the siren. The standard response is your business, delivered at your discretion.
Diaversarycommunity term: The anniversary of your diagnosis. Some people mark it with cake, some ignore it entirely, some get quietly weird for a day. All valid. It's the one anniversary nobody signed up for and everybody remembers.
DKA: Diabetic ketoacidosis: the medical emergency that develops when the body has too little insulin for too long, burns fat for fuel, and floods the blood with acidic ketones. Vomiting, deep breathing, fruity breath, confusion. DKA is an emergency-room situation, not a wait-and-see situation.

E

eAG: Estimated average glucose: an A1C translated into the same units your meter and CGM use, via a published population formula. It's the bridge between the lab's percentage and the numbers you look at every day. An estimate, not a measurement.
Endo: Short for endocrinologist, the specialist who manages T1D medically. The relationship works best as a partnership: they bring the medicine, you bring the lived data of your actual life. A good one is worth keeping.
Extended bolus: A pump feature that stretches a meal bolus over time instead of delivering it all at once, for food that digests slowly. Also called a square wave or dual wave depending on the pump's vintage. The tool the pizza effect was waiting for.

F

Feet on the floorcommunity term: The glucose rise that starts the moment you get out of bed, before coffee, before food, before anything. Standing up flips the liver into morning mode and it releases glucose to help. Deeply committed to being helpful. Related to dawn phenomenon but triggered by the act of getting up.
Fingerstick: The classic glucose check: lancet, drop of blood, test strip, meter. CGMs made it rarer, not extinct; it's still the tiebreaker when a sensor reading doesn't match how you feel. Rotating fingers is the difference between a habit and calluses.
Follow app: An app that lets someone else see your CGM numbers remotely: a parent, a partner, a friend on the nights that matter. Genuinely great for safety, genuinely fraught when it turns into surveillance. Worth an honest conversation about who watches and when.

G

Glucagon: The hormone that raises glucose, and the emergency medicine version of it used when a severe low makes eating impossible. Modern versions are a nasal puff or a ready-to-use pen. The people around you should know where yours lives and how to use it; that conversation takes five minutes and matters exactly once.
Glucose tabs: Chalky, aggressively fruit-flavored tablets of pure glucose for treating lows. Fast, precise, shelf-stable, and immune to the 'accidentally eat the whole bag' problem that gummy candy has. Nobody loves them. Everybody's glovebox has them.
Glycemic index: A ranking of how fast a food raises glucose. Juice sprints, lentils stroll. Useful as intuition (fast carbs for lows, slower carbs for staying power) rather than as homework; real meals mix speeds anyway.
Glycogen: The liver's stored glucose, kept for emergencies and exercise. It's what glucagon releases during a severe low, what empties during a long workout, and what the liver is restocking afterward, which is one reason lows can show up hours after the gym.
GMI: Glucose management indicator: an A1C-style number estimated from CGM data instead of a blood draw. Handy between labs, and famously willing to disagree with the actual lab result, because they measure different things over different windows. Trend, not verdict.

H

Honeymoon phase: The stretch after diagnosis when surviving beta cells rally and make some insulin again, making numbers easier and doses smaller. It can last months or years, and its ending can feel like failing. It isn't; it's the disease progressing on its own schedule, nothing you did.
Hyperglycemia (hyper): High glucose. Feels like thirst, fatigue, brain fog, a mouth like a desert, and a personality you'd rather not own. Everyone's threshold for 'high' is set with their care team; the feeling, though, is universal.
Hypoglycemia (hypo): Low glucose, the sharp edge of T1D. Shaky, sweaty, confused, hungry enough to eat the kitchen. Fast carbs fix it, waiting the hard part. Lows want treating first and analyzing later.
Hypoglycemia unawareness: When the body stops sending the warning signs of a low: no shakes, no sweat, just a number falling quietly. It can develop after years of frequent lows, and it's serious because the alarm system is the safety net. Very much a tell-your-care-team situation; awareness can often be rebuilt.

I

Infusion set: The tubing-and-cannula assembly that connects a pump to your body, changed every few days. The cannula sits under the skin and delivers the insulin. When people say their 'site' failed, this is usually the suspect.
Insulin pen: A pen-shaped injector with a dial for units and a tiny replaceable needle. Simpler than a pump, more civilized than a vial and syringe, and the backbone of MDI. Modern smart pens log doses, which quietly settles a lot of 'did I already inject' debates.
Insulin stacking: Taking a new correction while the last one is still working, because the number hasn't moved yet. The doses pile up, then hit together, then you're low. Insulin is slower than impatience. Insulin on board is the concept that keeps stacking in check.
Interstitial fluid: The fluid between cells, which is what a CGM actually measures. Glucose gets there a few minutes after it's in the blood, so CGM readings trail reality slightly, most noticeably when things are changing fast. Why a sensor can say one thing mid-sprint and a fingerstick another.
IOB (insulin on board): The insulin still active in your body from previous doses. Fast-acting insulin works for hours, not minutes, and IOB is the running tally. Pumps and AID systems track it constantly; it's the number that answers 'should I correct again or wait?'

J

Juice box mathcommunity term: The 3 a.m. arithmetic of treating a low: how many grams, how many boxes, how long to wait. Performed shaky, half-asleep, by flashlight, at the exact moment your brain has the least glucose to do math with. Every T1D household knows this genre of mathematics.

K

Ketones: Acidic byproducts of burning fat for fuel, which the body does when insulin is too scarce to use glucose. Small amounts happen to anyone; in T1D, rising ketones plus high glucose is the road toward DKA. Ketone strips are cheap and belong in the kit, especially for sick days and pump failures.

L

LADA: Latent autoimmune diabetes in adults: T1D that arrives slowly in adulthood, often misread as type 2 at first because of the age and the gradual onset. Same autoimmune process, gentler ramp. Many people with LADA spend a frustrating year being treated for the wrong disease.
Lancet: The tiny needle that pricks a finger for a glucose check. Officially changed after every use. The community's most honest running joke is how rarely that actually happens.
Lipohypertrophy: Lumpy, thickened tissue that builds up under skin that absorbs too many injections or pump sites in the same spot. Insulin absorbs erratically from it, which turns steady doses into mystery results. The fix is unglamorous and works: rotate your sites.
Liver dumpcommunity term: Community shorthand for the liver releasing stored glucose in one enthusiastic go: during stress, exercise, a bad low, or apparently just for fun. The technical crowd says 'hepatic glucose release.' Everyone else says the liver did a thing.
Looping (DIY): Running an automated insulin delivery system built by the T1D community itself, from open-source code, before commercial versions existed. The #WeAreNotWaiting movement built it out of impatience and love. DIY systems aren't regulator-approved, which is a real consideration to weigh with your care team, and their existence pushed the whole industry forward.

M

MARD: Mean absolute relative difference: the accuracy stat CGM makers publish, comparing sensor readings against lab references. Lower is better. Useful for comparing spec sheets, less useful for explaining why your sensor picked today to hallucinate.
MDI: Multiple daily injections: managing T1D with pens or syringes, typically long-acting insulin for basal plus fast-acting for meals. Not the fallback option; a fully modern way to run the disease that plenty of people prefer for its simplicity and its lack of things stuck to you.

N

No-hittercommunity term: A full day with every CGM reading in range. Borrowed from baseball, earned in the kitchen. Rare enough to screenshot, satisfying enough that people absolutely do.

O

Occlusion: A blockage in a pump's insulin path: kinked cannula, clogged line, insulin quietly not arriving. Pumps alarm when they notice, and they don't always notice fast. An unexplained stubborn high on a pump is an occlusion until proven otherwise.

P

Pizza effectcommunity term: The signature move of high-fat, high-carb food: glucose looks fine for hours, then climbs long after dinner is over, because fat slows digestion and stretches the carbs out. Named for its most famous perpetrator. The extended bolus was invented for exactly this.
Pod: A tubeless insulin pump worn directly on the skin as one self-contained unit, controlled from a phone or handheld. Omnipod is the household name. The trade: no tubing to snag on doorknobs, but the whole pod gets replaced every few days.
Prebolus: Taking mealtime insulin a stretch before eating instead of at the first bite, so the insulin and the food peak together instead of the food winning the opening lap. One of the highest-leverage habits in T1D, and the easiest to forget. How early depends on you, the meal, and your starting glucose; that's care-team territory.
Pump: A wearable device that delivers fast-acting insulin continuously: a background drip for basal, on-demand doses for meals. Trades injections for tubing, sites, and settings. Not better or worse than MDI, just a different set of trade-offs; the best system is the one you'll actually use.
Pump vacationcommunity term: A planned break from the pump, switching back to injections for a beach week, a burnout stretch, or just the urge to have nothing attached for a while. Completely legitimate, and it goes best planned with your care team rather than improvised at the airport.

R

Rage boluscommunity term: The oversized correction fired at a high that refuses to come down, powered by frustration rather than arithmetic. Universally relatable, rarely a good idea; the crash afterward tends to make the point. The antidote is boring: check the IOB, correct once, walk away from the graph.
Rebound high: The high that follows a low, from some blend of overtreating (the whole kitchen was right there) and the body's own stress hormones pushing glucose up. Treating lows with measured fast carbs instead of panic grazing is the counter, easier typed than done at 3 a.m.
Reservoir: The cartridge inside a pump that holds the insulin, refilled or swapped at site changes. Pod users have one too; it's just sealed inside the pod. The thing you check before a long weekend away from supplies.

S

Sensor: The disposable part of a CGM: a tiny filament under the skin reading glucose, worn for a week or two depending on the model. Applied with a spring-loaded applicator that looks scarier than it feels. Where all your data, and several of your feelings, come from.
Site change: The every-few-days ritual of moving a pump's infusion site or pod to fresh skin: old one off, new spot chosen, new set in. Skipping the 'fresh spot' part is how lipohypertrophy starts a collection.
Site failure: When a pump site stops delivering properly: bent cannula, irritated tissue, adhesive giving up, or no visible reason at all. The result is the same, insulin not arriving and glucose climbing. The fix is a new site, not a bigger correction through the failed one.
Somogyi effect: The old theory that an overnight low triggers a hormone rebound that causes a morning high. It's in every textbook; CGM data has made it controversial, with most studied morning highs tracing to dawn phenomenon or plain insulin shortfall instead. If your mornings are high, the answer is in your overnight data, not in folklore.
Sugar surfing: A style of management built on riding the CGM trend in real time: small, frequent nudges based on where glucose is heading rather than set-and-forget doses. Coined by Dr. Stephen Ponder, a T1D himself. The name is accurate; there are waves either way, and surfing them is a skill built with your care team.
SWAG boluscommunity term: Community acronym for a 'scientific wild-ass guess': the bolus you take when the food has no label, no menu, and no mercy. Casserole at a potluck, curry at a wedding. Experience narrows the guess. Nothing eliminates it.

T

T1D: Type 1 diabetes: the autoimmune kind, where the immune system takes out the insulin-producing beta cells and insulin comes from outside for life. Not caused by sugar, diet, or anything anyone did. Also the person: 'a T1D' is how the community often says it.
TDD: Total daily dose: all the insulin used in a day, basal and boluses together. Care teams use it as a reference point for sizing settings and spotting trends. It's an input to their math, not a score to compete on; bodies vary wildly and so do their TDDs.
Temp basal: A temporary change to a pump's background insulin rate for a set window: less for a hike, more for a sick day, whatever the situation calls for. One of the pump's best arguments for itself. AID systems essentially run tiny temp basals all day on your behalf.
Test strips: The single-use strips a glucose meter reads. Somehow simultaneously precious cargo and household confetti: guarded like gold at the pharmacy counter, found later in every pocket, bag, and car seat crack you own.
Time in range: The percentage of time glucose spends inside a target band, straight from CGM data. Many clinicians now treat it as more useful than A1C alone because it shows the shape of your days, not just the average. The band and the goal are personal, set with your care team.
Transmitter: The part of some CGM systems that clips onto the sensor and broadcasts readings to your phone or receiver. Newer systems build it into the disposable sensor; older ones make you keep track of it, charge it, and eventually mourn it.

U

Unicorncommunity term: A CGM reading of exactly 100, flat arrow, or more loosely any perfectly steady stretch of graph. Named for being magical and mostly mythical. Screenshotting one is not just allowed, it's encouraged.

W

Warmup period: The stretch after inserting a new CGM sensor when it's settling in and shows no data, from thirty minutes to two hours depending on the model. Always feels longer. Veterans time site changes so the warmup happens somewhere boring, not at dinner or bedtime.