Diabetes Glossary: 40+ T1D Terms Explained

Understanding diabetes management means learning a new language. This glossary defines the clinical terms you'll encounter in FlightGlucose and in real diabetes care — written in plain English, based on ADA 2024 guidelines.

Glucose Metrics

Time in Range (TIR)

The percentage of time glucose stays between 70–180 mg/dL. ADA 2024 recommends >70% TIR for most adults with T1D. The primary outcome measure for modern diabetes management alongside A1C.

A1C (HbA1c)

A blood test measuring average glucose over 2–3 months, expressed as a percentage. ADA target for most adults: below 7%. Does not capture glucose variability or hypoglycemia frequency.

Time Below Range (TBR)

Percentage of time glucose is below 70 mg/dL. ADA recommends keeping TBR below 4% for most patients.

Time Above Range (TAR)

Percentage of time glucose is above 180 mg/dL. ADA recommends keeping TAR below 25%.

Glucose Variability

How much glucose fluctuates throughout the day. High variability increases complication risk even when A1C is normal. Measured by coefficient of variation (CV); target CV below 36%.

GMI (Glucose Management Indicator)

An A1C estimate calculated from CGM data. Useful when lab A1C and CGM data disagree.

Insulin Terms

Bolus Insulin

Rapid-acting insulin taken to cover meals or correct high glucose. Examples: lispro (Humalog), aspart (NovoLog). Onset 15 min, peak 60–90 min, duration 3–5 hours.

Basal Insulin

Long-acting insulin that provides background coverage across 24 hours. Examples: glargine (Lantus), detemir (Levemir). Suppresses liver glucose output between meals and overnight.

Insulin on Board (IOB)

The amount of active insulin still working in the body from previous doses. Critical for avoiding stacking — taking too much insulin when a previous dose is still active.

Insulin Stacking

Giving additional bolus doses before previous insulin has finished working, risking severe hypoglycemia. IOB tracking prevents stacking.

Insulin-to-Carb Ratio (ICR)

How many grams of carbohydrate one unit of insulin covers. Example: ICR of 1:10 means 1 unit covers 10g carbs. Varies by person and time of day.

Correction Factor (ISF)

How much one unit of insulin lowers glucose in mg/dL. Also called Insulin Sensitivity Factor. Used to calculate correction doses.

Pre-bolus

Taking bolus insulin 10–20 minutes before eating to match insulin peak with glucose rise from the meal. Reduces post-meal spikes.

Dual Wave Bolus

A pump feature delivering part of the bolus immediately and the rest over hours. Used for high-fat meals that cause delayed glucose rise (pizza effect).

Pharmacokinetics

How the body absorbs, distributes, and eliminates a drug over time. Understanding insulin pharmacokinetics (onset, peak, duration) is essential for timing decisions.

Insulin Initiation

The process of starting insulin therapy for the first time. In T1D, insulin is initiated at diagnosis. In T2D, initiation typically begins with basal insulin when oral medications alone no longer maintain target glucose levels.

Insulin Intensification

Escalating insulin therapy by adding bolus insulin to basal, switching to a basal-bolus regimen, or adjusting doses. Required when current therapy fails to achieve glycemic targets.

Types of Insulin

Insulins are classified by speed: rapid-acting (lispro, aspart — onset 15 min), short-acting (regular — onset 30 min), intermediate-acting (NPH — onset 1–2 hrs), long-acting (glargine, detemir, degludec — onset 1–2 hrs, lasts 24+ hrs), and ultra-long-acting (degludec — lasts 42+ hrs).

Monitoring

CGM (Continuous Glucose Monitor)

A sensor worn on the body that measures glucose every 1–5 minutes. Examples: Dexcom G7, Libre 3. Provides trend arrows showing direction and rate of change.

CGM Lag

The 5–15 minute delay between blood glucose changes and CGM readings, because CGMs measure interstitial fluid, not blood directly. Most significant during rapid glucose changes.

Flash Glucose Monitor

A CGM variant requiring the user to scan a reader over the sensor to get a reading, rather than transmitting continuously. Example: FreeStyle Libre.

Finger Stick

Traditional blood glucose test using a lancet and glucometer. Still used to calibrate some CGMs and confirm CGM readings during rapid changes.

Trend Arrow

CGM indicator showing direction and rate of glucose change. A double down arrow means glucose is falling faster than 3 mg/dL per minute — immediate action needed.

Hypoglycemia

Hypoglycemia

Blood glucose below 70 mg/dL. Level 1: 54–70 mg/dL (treat). Level 2: below 54 mg/dL (urgent treatment). Level 3: severe — requires assistance from another person.

Rule of 15

Standard hypoglycemia treatment: 15g fast carbs, wait 15 minutes, recheck. Repeat if still below 70 mg/dL.

Glucagon

Emergency hormone that triggers the liver to release stored glucose. Used when a person is unconscious or unable to eat. Available as injection kit or nasal powder (Baqsimi).

Hypoglycemia Unawareness

Loss of ability to feel low glucose symptoms, often after years of T1D or frequent hypoglycemia. Increases severe hypo risk because the person cannot self-treat.

Nocturnal Hypoglycemia

Low glucose during sleep. Dangerous because symptoms may not wake the person. CGM alarms are the primary protection.

Rebound Hyperglycemia (Somogyi Effect)

High glucose following overnight hypoglycemia, as counter-regulatory hormones overcorrect. Controversial — often confused with dawn phenomenon.

Dawn Phenomenon

Natural glucose rise in early morning (4–8am) driven by cortisol and growth hormone. Requires higher basal rates or pre-dawn bolus in many T1D patients.

Hyperglycemia and Complications

Hyperglycemia

Blood glucose above 180 mg/dL. Symptoms: thirst, frequent urination, fatigue, blurred vision. Chronic hyperglycemia drives all long-term diabetes complications.

DKA (Diabetic Ketoacidosis)

Life-threatening emergency caused by insulin deficiency. Without insulin, the body burns fat for fuel, producing ketones that acidify the blood. Requires emergency hospital treatment.

Ketones

Acidic byproducts of fat metabolism. Small amounts are normal; levels above 0.6 mmol/L indicate insulin deficiency and require action.

HHS (Hyperosmolar Hyperglycemic State)

A severe hyperglycemic emergency more common in T2D, characterized by extreme glucose elevation (often >600 mg/dL) and severe dehydration without significant ketosis.

Technology

Insulin Pump

Device delivering continuous subcutaneous insulin via a catheter. Replaces multiple daily injections. Programmed with basal rates and delivers boluses via buttons or app.

Closed Loop / Artificial Pancreas

System linking a CGM to an insulin pump with an algorithm that automatically adjusts insulin delivery. Examples: Medtronic 780G, Omnipod 5, Tandem Control-IQ.

Open Loop

Traditional pump therapy where the patient manually decides all insulin doses. The pump delivers what the patient programs — no automatic adjustment.

PDM (Personal Diabetes Manager)

Handheld controller for tubeless insulin pumps like Omnipod. Programs doses remotely.

Lifestyle Factors

Carbohydrate Counting

Method of matching insulin doses to carbohydrate intake using the ICR. Foundation of modern T1D meal management.

Glycemic Index (GI)

Rating of how quickly a food raises glucose. High GI foods (white bread, glucose tablets) raise glucose rapidly. Low GI foods (lentils, oats) raise it slowly.

Pizza Effect

Delayed glucose spike 3–6 hours after high-fat meals, caused by fat slowing gastric emptying. Requires extended bolus strategies.

Exercise Effect

Aerobic exercise typically lowers glucose by increasing insulin sensitivity. Anaerobic exercise (sprints, weightlifting) can raise glucose through counter-regulatory hormone release.

Sick Day Rules

Protocol for managing T1D during illness: never stop insulin, check glucose and ketones every 2–4 hours, increase fluid intake, contact medical team if ketones rise.

Honeymoon Phase

Period after T1D diagnosis when residual beta cell function reduces insulin requirements. Lasts months to years. Ends as remaining cells are destroyed.

Managing Diabetes at School

Children with T1D require a diabetes management plan (504 Plan in the US) that covers insulin administration, glucose monitoring, snack access, and emergency procedures during school hours. School nurses and teachers must be trained in hypoglycemia recognition and glucagon administration.