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Understanding blood values: which value means what?

Fasting glucose, HbA1c, OGTT, time in range, hypoglycaemia: many values, easily confused. Here’s what the key blood-sugar numbers mean, where the limits are, and how they fit together.

Author: StoffwechselFit editorial teamLast updated: 21 Jul 2026

🌐 Translated from the German original. Wording has been localised for English readers; in case of doubt, the German version is authoritative.

Individual illustration: Understanding blood values: which value means what?
Understanding blood values: which value means what?

The key values at a glance

The most important blood-sugar values at a glance Overview of the central values. Fasting glucose: normal below 100, prediabetes 100 to 125, diabetes from 126 mg/dl (ADA; the WHO sets the lower prediabetes threshold at 110). HbA1c as the long-term value: normal below 5.7 percent, prediabetes 5.7 to 6.4, diabetes from 6.5. Two-hour value in the oral glucose tolerance test: normal below 140, impaired tolerance 140 to 199, diabetes from 200. Time in range from CGM: target more than 70 percent of the time between 70 and 180. Hypoglycaemia: below 70 level 1, below 54 level 2. The values are guideline orientation and do not replace medical assessment. The key values at a glance Guideline orientation: lab values belong in medical hands Value normal Precursor Diabetes Fasting glucose mg/dl < 100 100–125 ≥ 126 HbA1c (long-term) last ~2–3 months < 5.7% 5.7–6.4% ≥ 6.5% oGTT 2-Std-Value glucose load < 140 140–199 ≥ 200 2 h after eating Everyday < 140* Diabetes target < 180 individual Time in Range CGM (70–180) Target > 70% of the time in band Hypoglycaemia mg/dl < 70 (level 1) < 54 (level 2) help needed * Healthy usually < 140. Fasting thresholds per the ADA; the WHO sets the lower pre-stage threshold at 110. No self-diagnosis.
Fig. 1: The central blood-sugar values with their orientation ranges. Details and sources in the respective articles.

Three perspectives on the same metabolism

It becomes easiest when you sort the values by their time perspective: snapshot, everyday and long-term:

Fasting glucose measures the value after several hours without food: a morning assessment. Why it can be elevated despite fasting (the dawn phenomenon) is in Fasting blood sugar & the dawn phenomenon. The oral glucose tolerance test (OGTT) looks at how the body processes a defined amount of sugar: details in OGTT explained.

How much blood sugar rises after meals is shown by the value after eating. Anyone wearing a CGM also sees the Time in Range (TIR), for me the most honest everyday metric, because it captures the whole day instead of single measurement points.

The HbA1c is the “long-term blood-sugar value” and roughly reflects the last two to three months. It’s central to diagnosis and monitoring: in detail in HbA1c explained. Important: HbA1c and TIR complement each other but don’t replace one another.

When it gets too low: hypoglycaemia

It’s not only high values that count. From below 70 mg/dl we speak of hypoglycaemia (level 1), below 54 mg/dl of a more serious one (level 2). This is mainly relevant for people on insulin or certain tablets, the details and the 15-15 rule are in Recognising hypoglycaemia.

Key takeaways

  • Fasting glucose & OGTT = snapshot; post-meal values & TIR = everyday; HbA1c = long-term.
  • Diabetes thresholds: fasting ≥ 126, HbA1c ≥ 6.5%, OGTT 2-hour ≥ 200.
  • Time in Range (CGM): target usually > 70% between 70 and 180 mg/dl.
  • Hypoglycaemia: below 70 (level 1), below 54 (level 2).
  • A single value says little – the context counts, interpreted medically.
Related

Knowledge → HbA1c explained
Knowledge → Fasting blood sugar & the dawn phenomenon
Knowledge → OGTT explained
Knowledge → Blood sugar after eating
Knowledge → Understanding CGM
Knowledge → Recognising hypoglycaemia

Article ID: SWF-W-005Please quote this ID for corrections or additions.

Sources

Sources as of: 21 Jul 2026.

  1. Diagnostic thresholds (fasting, HbA1c, OGTT). American Diabetes Association. diabetes.org (opens in a new window)
  2. Time in Range international consensus: target > 70% at 70–180 mg/dl. Diabetes Care. care.diabetesjournals.org (opens in a new window)
  3. Hypoglycaemia levels (< 70 / < 54 mg/dl); standards of care. ADA. diabetesjournals.org (opens in a new window)

Medical note: General, source-informed information for orientation, not medical advice or diagnosis. A single value says little; lab values belong in medical hands. No promise of cure.

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