Normal/abnormal glucose metabolism

This graph shows the change in blood glucose levels over time, typically during an oral glucose tolerance test (OGTT).

The different curves illustrate various states of glucose metabolism.

 

Interpretation of the curves

Normal glucose metabolism (green, dashed)

The fasting value is low, the increase after the load is moderate, and by the 120th minute, blood glucose levels return to the baseline range (usually below 7.8 mmol/l).

 

Impaired Glucose Tolerance (IGT - blue, dashed)

The fasting value may still be normal, but the 120-minute value is abnormally high, ranging between 7.8 and 11.0 mmol/l.

 

Elevated Fasting Glucose (IFG - black, continuous)

The baseline (0-minute) value is already higher than normal (6.1–6.9 mmol/l), indicating a disorder in the body's regulation after fasting.

 

Combined IGT and IFG (red, dotted)

This is the most severe prediabetic state, where both fasting and post-load values are significantly elevated, but have not yet reached the level of manifest diabetes. 

 

Diagnostic Thresholds (mmol/l)

Condition: Fasting (0 min) and 120-minute value

• Normal < 6.1 and < 7.8
• IFG 6.1-6.9 and < 7.8
• IGT < 7.0 and 7.8-11.0
• Diabetes ≥ 7.0 and ≥ 11.1

These values illustrate different stages of carbohydrate metabolism disorders, which can be considered precursors to type 2 diabetes. 

 

Normal glucose metabolism (green)

The lowest blood glucose level is seen after fasting (0 minutes), then rises quickly after glucose loading, but returns relatively quickly to the baseline value, indicating good insulin response and glucose utilization by the body.

Impaired Glucose Tolerance (blue - IGT)

Here, the blood glucose increase is greater, especially around the 60th minute after loading, but eventually returns close to the initial value – this indicates a mild disturbance in glucose processing, but it is still reversible.

Elevated Fasting Glucose (black - IFG)

The curve starts with a higher blood glucose value even on an empty stomach, and reaches a higher peak after the load than normal.

This is a sign of early metabolic disorder, when nocturnal blood glucose reduction is primarily insufficient.

Combined IGT and IFG (red)

In this case, both the fasting value and the peak after glucose loading are higher than in the previous cases, and blood glucose returns more slowly to baseline.

This is the most severe disorder among the four, indicating significant insulin resistance and impaired glucose regulation.

 

The essence

The greater the increase in blood glucose, and the higher the fasting and returning values, the more severe the glucose metabolism disorder, indicating a risk of developing diabetes.