What is HbA1c?
Glucose in your blood attaches itself slowly and by itself to haemoglobin, the protein your red blood cells carry oxygen with. The more glucose circulates, the more haemoglobin gets sugared like that, and that layer stays as long as the cell lives. A red blood cell lasts about 120 days. So what you measure is not a snapshot but the average of your blood sugar over the preceding 8 to 12 weeks, with the most recent weeks weighing heaviest. That makes HbA1c the most honest blood sugar number there is. A fasting glucose can be made to look good with one good night and an empty stomach; HbA1c cannot. It adds up every meal, every dessert and every walk of the past months, without your being able to stage any of it. The reverse holds too: one festive weekend does not show in it. Your report shows HbA1c as one number in mmol/mol. Normal is 20 to 42 mmol/mol, and unlike many values in this library almost every lab in the Netherlands uses exactly that range. If you come across a percentage online, that is the older scale; the table further down shows how the two relate.
Why is HbA1c relevant?
HbA1c shows where your blood sugar stands on average, and that is exactly the number that counts in the long run. A blood sugar that hangs on the high side for years slowly damages the small blood vessels of the eyes, kidneys and nerves and speeds up atherosclerosis in the large ones. That happens gradually and you notice nothing of it, until it is far along. Anyone who knows their HbA1c sees that direction years before their symptoms. For anyone who wants to stay healthy, the top of the normal range is more interesting than the diabetes threshold. Insulin resistance, the metabolism that needs ever more insulin to reach the same blood sugar, builds up over years, and in those years the HbA1c creeps up slowly, from the low thirties to the high thirties and then past 42. Above 42 mmol/mol you are above normal; from 48 mmol/mol the international threshold for diabetes applies. In the Netherlands, incidentally, diabetes is not diagnosed on HbA1c but on fasting glucose, and HbA1c then serves to follow how things go. For you as a healthy reader it is above all the value that shows whether you are moving the right way, before anything needs to be diagnosed.
HbA1c reference ranges
What counts alongside the number:
- Your fasting glucose: the snapshot next to the average
- Triglycerides and HDL, which often betray insulin resistance earlier than blood sugar does
- Your waist, exercise and sugar intake, the levers the number responds to
- Your haemoglobin and ferritin, because anaemia and iron deficiency distort the measurement
- The trend over six months or longer, rather than one result
Dutch labs report HbA1c in mmol/mol, the IFCC scale, and almost all use the same range: 20 to 42 mmol/mol. The two rows below are limits for anyone who has or is developing diabetes, not normal values; they are there because a result is read against them.
What Dutch labs actually use
All four laboratories publish 20 to 42 mmol/mol, and all four report in mmol/mol. There is no spread to bridge here.
20 – 42mmol/mol
Outside this range every lab calls it abnormal.
every lab calls 20 – 42 mmol/mol normal. Outside that range every lab calls it abnormal.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | All adults, not diabetic | 20-42 mmol/mol |
| Star-shl2026 | All adults | 20 - 42 mmol/mol |
| Certe2026 | All ages | 20 - 42 mmol/mol |
| Clinical Diagnostics2026 | All adults | 20-42 mmol/mol |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
HbA1c high or low: what it means
A higher HbA1c almost always means a higher average blood sugar, and that usually comes from the same pattern: belly fat, little exercise, plenty of sugar and fast carbohydrates, little muscle mass, and the insulin resistance that grows out of them. Lack of sleep and persistent stress depress insulin sensitivity too. Occasionally a high HbA1c is not a blood sugar problem but a blood problem: with iron deficiency, red blood cells live longer and get more sugared, and the value falls again once the iron is replenished. A low HbA1c is usually simply a low average blood sugar, and that is favourable. There is a second route that has nothing to do with sugar: anything that shortens the life of red blood cells, such as recovery after blood loss or an anaemia from breakdown, lowers the value without your blood sugar falling. Very intensive endurance athletes sometimes see the same, because their red blood cells wear out faster. A low HbA1c next to a normal glucose is then no cause for concern, but it is a reason to take the number less literally. HbA1c listens to what you do, only slowly: count on two to three months before a change is fully in the number. The levers are those of blood sugar itself. Less sugar, soft drinks, juice and white carbohydrates, and more fibre from vegetables, legumes and whole grains, so that glucose enters your blood more slowly. Losing weight around the middle, because belly fat is the engine of insulin resistance. Daily movement, and a walk after meals in particular: muscles take up glucose without insulin having to be involved. Strength training, because more muscle is more room to put glucose. For most people without diabetes that is the whole solution; with diagnosed diabetes it remains the foundation and medication joins it where needed. Read HbA1c beside your fasting glucose, which gives the snapshot, and beside triglycerides and HDL, which often betray the metabolic pattern earlier than blood sugar itself. And read it as a trend: the same test six months later says more than one loose result.
What lowers it
A lower average blood sugar, and beyond that anything that shortens the life of red blood cells.
| Cause | How often |
|---|---|
| Lower average blood sugarThe ordinary explanation, and the favourable one: the value follows your glucose over the preceding weeks | Often |
| Recovery after acute blood lossYoung red blood cells have picked up little glucose yet, and that depresses the value temporarily | Sometimes |
| Haemolytic anaemiaRed blood cells that are broken down early have less time to get sugared | Sometimes |
| Endurance trainingIn runners an average red cell lifespan of 67 days has been measured against 113 days in non-athletes, and shorter survival depresses the result | Rare |
What raises it
Mostly a higher average blood sugar, and beyond that the iron route.
| Cause | How often |
|---|---|
| Higher average blood sugarMore glucose in your blood means more glucose on your haemoglobin; belly fat, little exercise and plenty of sugar are the usual causes | Often |
| Iron deficiency anaemiaRed blood cells then live longer and get more sugared; the value falls again once the iron is replenished | Sometimes |
| Late pregnancyIn women without diabetes the value rises late in pregnancy, mainly through iron deficiency | Rare |
How does a HbA1c blood test work?
- Referral
- Not needed. You can have HbA1c measured without going through a doctor first.
- Fasting
- Not needed. Your breakfast does not shift a value built up over months; that is the big practical difference from fasting glucose.
- The draw
- One tube of blood from a vein in your arm. The measuring method differs per lab, and yet they arrive at the same range.
- The result
- A single number in mmol/mol, in the same unit at every Dutch lab. Usually available within 24 hours.
- Repeating
- Because the value is built up over 8 to 12 weeks, testing again sooner adds little. If you change what you eat or start moving more, measure again after three months; then the effect is fully in.
- Which test
- HbA1c is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is HbA1c?
HbA1c measures how much of your haemoglobin is sugared. Glucose in your blood attaches itself slowly to haemoglobin, and that stays as long as the red blood cell lives. Because those cells last several months, the result gives an average over that period. One meal or one bad day therefore does not move it.
What is a normal HbA1c level?
Almost every Dutch lab uses the same range for anyone without diabetes: 20 to 42 mmol/mol. On the older scale in percentages that comes to about 4.0 to 6.0 percent. For anyone who wants to stay healthy, the top of that range is the most interesting: an HbA1c creeping towards 42 over the years shows that blood sugar is moving the wrong way.
Why does my report say mmol/mol and not a percentage?
Because Dutch labs have reported exclusively in mmol/mol since 2011. The percentage belongs to the older scale, which is still common online and in foreign sources. They are two scales for the same measurement: 42 mmol/mol is 6.0 percent, 48 is 6.5 percent and 53 is 7.0 percent. The Optimize app shows the same unit as your report.
What does a high HbA1c mean?
That your average blood sugar over the past two to three months was higher, usually from belly fat, little exercise and plenty of sugar and fast carbohydrates. Above 42 mmol/mol you are above normal; from 48 mmol/mol the international threshold for diabetes applies. In the Netherlands that diagnosis is made on fasting glucose, so a high HbA1c is a reason to put that beside it.
What does a low HbA1c mean?
Usually nothing special: the value follows your average blood sugar and that can simply be low. There is a second route, though. HbA1c measures haemoglobin that lasts for months, so if your red blood cells live shorter, after blood loss or with an anaemia from breakdown, the result falls without your blood sugar falling.
How do I lower my HbA1c?
With the levers of blood sugar itself: less sugar, soft drinks, juice and white carbohydrates, more fibre from vegetables, legumes and whole grains, losing weight around the middle, daily movement with a walk after meals, and strength training for more muscle. Count on two to three months before it is fully in the number. With diagnosed diabetes this remains the foundation and medication joins it where needed.
Do Dutch GPs diagnose diabetes on HbA1c?
No. The diagnosis rests on two fasting glucose values of 7.0 mmol/L or higher on two different days; HbA1c then serves to follow how things go. Internationally 48 mmol/mol counts as the threshold for diabetes, and an HbA1c near that is a reason to have a fasting glucose measured beside it.
Which tests include HbA1c?
HbA1c is in the Blood sugar & metabolism test (€59, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Read on
Sources
- 1.NHG guideline on type 2 diabetes (M01), Dutch College of General Practitioners. 2026. richtlijnen.nhg.org
- 2.WHO, Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus, abbreviated report of a WHO consultation. 2011. iris.who.int
- 3.NVKC, introduction of the new HbA1c reporting units (Dutch), Ned Tijdschr Klin Chem Labgeneesk. 2010. nvkc.nl
- 4.NGSP, Factors that interfere with HbA1c test results. 2026. ngsp.org
- 5.Weight, Byrne and Jacobs, Haemolytic effects of exercise, Clinical Science. 1991. pubmed.ncbi.nlm.nih.gov
- 6.Sacks, A1C versus glucose testing: a comparison, Diabetes Care. 2011. pmc.ncbi.nlm.nih.gov
- 7.Unilabs, test catalogue (Dutch): HbA1c. 2026. bepalingenklapper.nl
- 8.Star-shl, test catalogue (Dutch): HbA1c. 2026. star-shl.nl
- 9.Certe, test catalogue (Dutch): HbA1c-IFCC. 2026. bepalingenwijzer.certe.nl
- 10.Clinical Diagnostics, lab guide (Dutch): HbA1c. 2026. clinicaldiagnostics.nl
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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