Glossary

Twelve terms you will keep meeting in lab reports, doctor’s appointments and on this website – each explained in two to three sentences, with thresholds in mg/dl and mmol/l. The values are general guidance; you set your personal targets together with your care team.

HbA1c

HbA1c is the share of the red blood pigment haemoglobin to which glucose has attached, and it reflects average blood glucose over roughly the past eight to twelve weeks. Values below 5.7 % are considered normal, 5.7–6.4 % prediabetes and 6.5 % or higher diabetes. The value shows the average, not the fluctuations – two people with the same HbA1c can have very different curves.

Fasting blood glucose

Fasting blood glucose is the glucose concentration in the blood after at least eight hours without food, usually measured in the morning before breakfast. Values below 100 mg/dl (5.6 mmol/l) are considered normal, 100–125 mg/dl (5.6–6.9 mmol/l) impaired fasting glucose, and 126 mg/dl (7.0 mmol/l) or higher – measured on two separate days – diabetes. Stress, poor sleep and the dawn phenomenon can push the morning value upwards.

HOMA-IR

HOMA-IR is a calculated value for insulin resistance derived from fasting glucose and fasting insulin (glucose in mg/dl times insulin in µU/ml divided by 405). Values around 1 are considered unremarkable, while values above roughly 2 to 2.5 indicate insulin resistance depending on the laboratory. The index is an estimate and varies with daily condition and measurement method, so it is only meaningful together with other findings.

TyG index

The TyG index is a calculated value from fasting triglycerides and fasting glucose that can indicate insulin resistance without measuring insulin. It is calculated as the natural logarithm of (triglycerides in mg/dl times glucose in mg/dl divided by 2); values above roughly 8.5 to 8.8 are regarded in studies as a sign of insulin resistance. Because both inputs are part of standard laboratory panels, the index is inexpensive and easy to repeat.

Time in Range (TIR)

Time in Range is the share of time during which a glucose value measured by CGM lies within the target range of 70–180 mg/dl (3.9–10.0 mmol/l). For most adults with diabetes a share above 70 % is the goal, which corresponds to just under 17 hours a day. Time below range and time above range are considered in addition, because hypoglycaemia should be as rare as possible.

GMI

The Glucose Management Indicator (GMI) is an estimate calculated from the CGM mean that indicates which HbA1c the measured average roughly corresponds to. The formula is GMI (%) = 3.31 + 0.02392 × mean glucose in mg/dl. The GMI can differ from the laboratory HbA1c by a few tenths of a percent because it reflects only the sensor period and does not know individual differences in haemoglobin.

Dawn phenomenon

The dawn phenomenon is a rise in blood glucose in the early morning hours, roughly between 3 and 8 a.m., without anything having been eaten. It is caused by the early-morning rise of counter-regulatory hormones such as cortisol and growth hormone, which prompt the liver to release glucose; with insulin resistance or too little insulin action, the insulin response is not sufficient to absorb this rise. It explains why the fasting value in the morning can be higher than the value before going to bed.

Insulin resistance

Insulin resistance means that muscle, liver and fat cells respond less strongly to insulin, so the pancreas has to release more of it to keep blood glucose in range. It often develops years before type 2 diabetes and goes unnoticed for a long time because blood glucose initially stays normal. Exercise, weight loss and sleep can measurably improve insulin sensitivity.

Remission

Remission of type 2 diabetes means, according to the international definition, that HbA1c is below 6.5 % (48 mmol/mol) at least three months after all glucose-lowering medication has been stopped. Remission is not a cure: the predisposition remains and the diabetes can return, which is why regular check-ups are still necessary. Stopping medication always belongs in the hands of a doctor.

CGM

CGM stands for continuous glucose monitoring: a small sensor on the upper arm or abdomen measures glucose in the interstitial fluid under the skin around the clock and transmits the values to a reader or smartphone. Because interstitial fluid lags the blood by several minutes, the reading can be delayed during rapid changes. The benefit lies in the trend: you see rises, falls and patterns that a single blood test would never show.

Glycaemic index (GI)

The glycaemic index describes how strongly a carbohydrate-containing food raises blood glucose compared with glucose itself (GI = 100). Values up to 55 are considered low, 56–69 medium and 70 or above high. The GI says nothing about portion size; that is what the glycaemic load is for, and the actual response additionally depends on preparation, accompanying foods and on you.

Prediabetes

Prediabetes is a precursor of type 2 diabetes in which blood glucose values are above the normal range but still below the diabetes threshold: HbA1c 5.7–6.4 %, fasting glucose 100–125 mg/dl (5.6–6.9 mmol/l) or a 2-hour value in the oral glucose tolerance test of 140–199 mg/dl (7.8–11.0 mmol/l). At this stage, lifestyle changes can often delay or prevent progression to diabetes. That is why it pays to take the values seriously before symptoms appear.