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.

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.

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.