Insulin Clinics / Special situations

Glossary

Plain definitions of the terms used across this site. Each entry is short on purpose; the linked pages go deeper.

Medically reviewed by [Name, MD] · Last reviewed: [Month YYYY]

A B C D E F G H I K L M N P R S T U

A

A1C (HbA1c)

A blood test that estimates your average blood glucose over the previous 2–3 months by measuring the percent of hemoglobin molecules with glucose attached. An A1C of 7% corresponds roughly to an average glucose of 154 mg/dL.

Analog insulin

An insulin whose molecule has been slightly modified from the human form to change how fast it absorbs or how long it lasts. Most modern insulins (lispro, aspart, glargine, degludec) are analogs.

Authorized generic

The same insulin product as the brand-name version, made by the same manufacturer, sold under a generic label at a lower price. Lispro, aspart, and glargine all have authorized generics.

B

Basal insulin

The slow, steady background insulin that keeps fasting and between-meal glucose stable. Long-acting insulins like glargine and degludec are basal insulins; in pumps, the continuous trickle of rapid-acting insulin is also called basal.

Beta cell

The cell in the pancreas that makes insulin. Beta cells are destroyed in type 1 diabetes; in type 2 diabetes their function declines gradually over years.

Biosimilar

A version of a biologic medicine — like insulin — made by a different manufacturer to closely match an existing approved product. "Interchangeable" biosimilars (Semglee, Rezvoglar) can be substituted at the pharmacy without contacting the prescriber.

Bolus

A discrete dose of mealtime or correction insulin, as opposed to the continuous basal trickle. "Bolus insulin" usually means rapid- or short-acting insulin.

C

Carbohydrate (carb)

The component of food that is most strongly tied to mealtime blood glucose rises. Carbs are listed in grams on food labels.

Carb counting

The practice of estimating grams of carbohydrate in a meal so a mealtime insulin dose can be matched to the food.

CGM (continuous glucose monitor)

A wearable sensor that measures glucose in interstitial fluid every few minutes and sends readings to a phone, receiver, or pump. Examples include Dexcom G7, FreeStyle Libre, and Medtronic Simplera.

Closed-loop system

A pump and CGM that talk to each other, with software that adjusts insulin delivery automatically based on current and predicted glucose. "Hybrid" closed-loop still requires the user to announce meals.

Correction factor (insulin sensitivity factor, ISF)

How far one unit of mealtime insulin will lower your blood glucose. A correction factor of 50 means one unit lowers glucose by about 50 mg/dL.

D

Dawn phenomenon

A natural rise in blood glucose in the early morning hours before waking, driven by hormone shifts. Often shows up as a higher-than-expected fasting reading.

Detemir

A long-acting analog basal insulin (Levemir) lasting roughly 20 hours; sometimes dosed twice daily.

Degludec

An ultra-long-acting analog basal insulin (Tresiba) lasting more than 24 hours, with a flat profile and flexible timing.

DKA (diabetic ketoacidosis)

An emergency caused by too little insulin: the body breaks down fat for fuel, producing acidic ketones that build up in the blood. Most common in type 1 diabetes; possible in type 2. Symptoms include high glucose, nausea, vomiting, fruity breath, and rapid breathing.

E

Endocrinologist

A physician who specializes in conditions of the hormone-producing glands, including diabetes. Often the prescriber for type 1 diabetes and complex type 2 diabetes.

Euglycemic DKA

DKA that occurs at lower blood glucose than usual (sometimes under 250 mg/dL), most often associated with SGLT2 inhibitor medications, severe illness, pregnancy, or low food intake in someone using insulin.

F

Fasting glucose

Blood glucose measured after at least 8 hours without eating, typically first thing in the morning. The most useful single reading for adjusting basal insulin.

G

Gestational diabetes

High blood sugar that develops during pregnancy in someone who did not have diabetes before. Usually resolves after delivery; raises long-term risk of type 2 diabetes.

Glargine

A long-acting analog basal insulin (Lantus, Basaglar, Semglee at U-100; Toujeo at U-300). Lasts roughly 20–24 hours at U-100 and longer at U-300.

Glucagon

A hormone that signals the liver to release stored glucose. Available as nasal (Baqsimi) or pre-filled injection (Gvoke, Zegalogue) for emergency treatment of severe low blood sugar.

Glucose

The sugar that circulates in the blood and fuels most cells. Blood glucose is what insulin lowers and what diabetes management revolves around.

H

Hyperglycemia

High blood glucose. There is no universal cutoff, but "high" often means above 180 mg/dL after meals or above 130 fasting.

Hypoglycemia

Low blood glucose. The standard alert threshold is below 70 mg/dL; below 54 is considered clinically significant.

Hypoglycemia unawareness

Loss of the early warning symptoms of low blood sugar, often after frequent lows. Can be partly reversed by avoiding lows for several weeks.

I

Inhaled insulin (Afrezza)

A powdered rapid-acting insulin breathed in at meals. Not for basal coverage; not appropriate for people with chronic lung disease.

Insulin pump

A small device that delivers rapid-acting insulin continuously through a tube and cannula, or through a wearable patch (pod). Most modern pumps work with a CGM in a closed-loop system.

Insulin-to-carb ratio (I:C)

How many grams of carbohydrate are covered by one unit of mealtime insulin. A 1:10 ratio means one unit covers ten grams of carbs.

Interstitial fluid

The fluid between cells, where CGM sensors measure glucose. Lags behind blood glucose by 5–15 minutes when glucose is changing fast.

K

Ketones

Acidic compounds the body produces when it breaks down fat for fuel. Small amounts after fasting are normal; larger amounts in someone with diabetes can signal DKA.

Kussmaul breathing

Deep, rapid breathing seen in DKA as the body tries to blow off acid through the lungs. A late, urgent sign.

L

LADA (latent autoimmune diabetes in adults)

A slow-developing autoimmune diabetes in adults, sometimes called type 1.5. Often initially misdiagnosed as type 2; eventually requires insulin.

Lipohypertrophy

Soft, rubbery lumps under the skin from repeated insulin injections in the same spot. Cause erratic absorption and higher insulin needs. Prevented by good rotation.

Lispro

A rapid-acting analog insulin (Humalog, Admelog). Lispro-aabc (Lyumjev) is the ultra-rapid version.

M

mg/dL

Milligrams per deciliter — the U.S. unit for blood glucose. To convert to mmol/L, divide by 18.

mmol/L

Millimoles per liter — the unit for blood glucose used in most countries outside the U.S. To convert to mg/dL, multiply by 18.

MODY (maturity-onset diabetes of the young)

A group of inherited forms of diabetes caused by single-gene mutations affecting insulin production. Some respond to oral medications; others need insulin. Diagnosed by genetic testing.

N

NPH

Intermediate-acting human insulin (Humulin N, Novolin N, ReliOn N). Peaks 4–8 hours after injection; usually given twice daily. Lower-cost option.

P

Pancreas

The gland behind the stomach that makes insulin (in beta cells) and glucagon (in alpha cells), along with digestive enzymes.

Pen needle

The disposable needle that screws onto an insulin pen for each injection. Modern guidance is to use a 4 mm needle for almost everyone.

Postprandial

After a meal. Postprandial glucose readings are usually checked 1–2 hours after the start of a meal.

Prandial

Related to a meal. Prandial insulin is mealtime (rapid- or short-acting) insulin.

Premixed insulin

A combination of intermediate and short- or rapid-acting insulin in a single pen, taken twice daily. Examples: 70/30, 75/25, 50/50.

Prime (priming)

Pushing a small amount of insulin out of a pen before injecting, to clear air from the needle and confirm the pen is working. Usually 2 units.

R

Rapid-acting insulin

Insulin that begins working within about 15 minutes and lasts 3–5 hours. Used for meals and corrections. Examples: lispro, aspart, glulisine.

Regular insulin

Short-acting human insulin (Humulin R, Novolin R, ReliOn R). Slower onset (~30 minutes) than analogs; lower-cost option.

Rotation

Moving each injection to a slightly different spot to prevent lipohypertrophy. Within a region, stay at least one finger-width from the last injection.

S

Sliding scale

A fixed table of correction insulin doses based on blood glucose readings. Sometimes used in hospitals; not recommended as the only insulin in ongoing outpatient care.

Stacking

Adding more correction insulin while a previous dose is still working. The most common cause of unexpected lows. Most rapid-acting insulin keeps working for 3–5 hours.

Subcutaneous

The layer of fat just under the skin, where insulin is injected. Pen needles 4 mm long reliably reach this layer.

T

Time in range (TIR)

The percentage of CGM readings within 70–180 mg/dL. The standard goal for many adults is 70 percent or more. Captures both average and variability better than A1C alone.

Titration

Adjusting an insulin dose in small steps based on patterns over several days, rather than reacting to single readings.

Total daily dose (TDD)

All insulin, basal and bolus combined, in 24 hours. Many other dose calculations are anchored to TDD.

Type 1 diabetes

An autoimmune disease where the immune system destroys the insulin-producing beta cells. Always requires insulin.

Type 2 diabetes

A combination of insulin resistance and a relative shortage of insulin. Often managed with lifestyle and medications; some people eventually need insulin.

U

U-100

The standard insulin concentration: 100 units of insulin per milliliter. Most insulins, syringes, and pens are calibrated to U-100.

U-200

An insulin concentration of 200 units per milliliter, used in some pens (e.g., degludec U-200) for people who need large doses.

U-300

An insulin concentration of 300 units per milliliter, used in glargine U-300 (Toujeo). The pen counts in units regardless of concentration.

U-500

A high-concentration regular insulin (500 units per milliliter) used for severe insulin resistance. Requires special prescribing because of the risk of dosing errors with U-100 syringes.

Unit

The standard measure of insulin dose. Insulin pens and syringes are marked in units, not milliliters.