Diabetes blood test: what glucose and HbA1c say about your blood sugar

Glucose, your body's fuel, comes from the carbohydrates in your food and is carried through the blood to your cells. The hormone insulin, made in the pancreas, allows the cells to take up that glucose. In type 2 diabetes the cells respond less well to insulin, or the pancreas produces too little of it. The glucose then stays in the blood longer and blood sugar rises.

Glucose measures the amount of sugar in your blood at the time of the draw. That value moves through the day with what you eat, drink and do; it is a snapshot. HbA1c works differently. It stands for haemoglobin A1c: the red pigment in your blood cells to which glucose has attached itself. The higher your blood sugar over the past weeks, the more glucose sticks to the haemoglobin. Because red blood cells live for roughly two to three months, HbA1c reflects your average blood sugar over that whole period, independent of what you ate that day. The laboratory reports HbA1c in mmol/mol, a different unit from the mmol/l of a glucose measurement or a finger-prick test; the two numbers therefore cannot be compared with each other.

Together these two values tell you more than either alone: a single glucose value can be temporarily elevated, for example shortly after a meal or under stress, while the HbA1c shows whether your blood sugar has been on the high side over a longer period. Want to measure it yourself? Choose the HbA1c test or first read how HbA1c works.

Many people with an elevated blood sugar notice nothing for a long time. Symptoms that can go with it are:

• excessive thirst and a dry mouth
• frequent urination, including at night
• persistent fatigue
• blurred vision
• losing weight without trying
• wounds that heal poorly
• infections that keep coming back

These symptoms are non-specific. They also occur with lack of sleep, stress, a thyroid problem or a shortage of iron or vitamins, and often nothing serious is going on. Conversely, the absence of symptoms does not rule out an elevated blood sugar: the Dutch Diabetes Fund estimates that hundreds of thousands of people in the Netherlands have diabetes without knowing it, precisely because the early symptoms are vague. If you recognise a large part of these symptoms, measuring can give insight into your blood sugar.

Four values come into play when your blood sugar is examined. Each tells you something different.

• Fasting glucose: your blood sugar at the time of the draw, after at least eight hours without food or drink, water excepted. The value is sensitive to the day itself: acute stress, illness and certain medicines, such as corticosteroids and some diuretics, can raise it temporarily.
• HbA1c: your average blood sugar over the past two to three months. This value smooths out daily fluctuations and therefore depends less on the moment of the draw. It is less reliable with anaemia, iron deficiency, an abnormal type of haemoglobin such as in sickle cell disease, or after major blood loss, because the production and lifespan of the red blood cells then differ from usual.
• Triglycerides: a blood fat that is often elevated when sugar metabolism is disturbed.
• Cholesterol: counts together with blood sugar and blood pressure in the risk of cardiovascular disease.

None of these values says on its own whether you have diabetes; they gain meaning in combination with your symptoms, your weight, your family history and your medication.

Many people search for the normal HbA1c value or a normal glucose value. We deliberately do not quote those numbers, and that is not evasion.

A reference value is the range within which the results of roughly 95 percent of healthy people fall. That also means that roughly 5 percent of healthy people have a result just outside that range without anything being wrong. Laboratories set their own reference values, matched to their own measuring method, and the units can differ. The number you read somewhere online therefore need not apply to the laboratory that examines your blood.

On top of that, a threshold for a diagnosis is something different from a reference value, and the same value means something different for each person: in pregnancy, with anaemia, with diabetes medication or corticosteroids and at an older age, a doctor weighs a result differently. That is why your report shows the reference value of the performing laboratory next to your own value, with an explanation from our doctor. The laboratory leads, the doctor weighs; that is more precise than one number for everyone.

Type 2 diabetes is more common with overweight, little exercise and diabetes in the family. Thuisarts.nl, the patient website of the Dutch College of General Practitioners, names a higher chance from around the age of 45 combined with one or more of these points:

• overweight
• type 2 diabetes in the family
• high blood pressure or raised cholesterol
• little exercise
• smoking
• cardiovascular disease, or an increased risk of it
• a Turkish, Moroccan or Surinamese background; with a Hindustani background the higher chance applies from the age of 35
• gestational diabetes in the past

If you recognise yourself in one or more of these points, preventive testing can give insight: not to diagnose yourself, but to know where you stand. If your blood sugar turns out to be elevated, you know that at a stage where there is often still plenty of room to adjust. Through your GP, the advice for this group is a measurement once every three years, and annually in the first years after gestational diabetes.

An elevated blood sugar rarely stands alone. When sugar metabolism is disturbed, blood fats are often abnormal too: cholesterol and triglycerides can then be elevated. This combination is so common that doctors prefer to assess these values together.

That is more than a practical choice. Blood sugar and blood fats weigh together in the risk of cardiovascular disease. If you have your blood sugar measured, adding these fat values gives you a fuller picture of that risk, from the same draw. Our doctor notes in the written explanation how the values relate to each other.

A blood test on your own initiative fits four situations, the same four for which our blood sugar test was put together:

• Family history: type 2 diabetes runs in your family and you want to know where you stand.
• Increased risk: you are overweight or exercise little and want to see your risk.
• Periodic monitoring: you want your blood sugar followed annually, for example because you are working on your lifestyle.
• Follow-up: you previously had an abnormal value and want to see the trend.

In three situations your GP is the first step:

• You have clear symptoms, such as excessive thirst, frequent urination, unintentional weight loss or blurred vision; then a prompt assessment is needed.
• You have already been diagnosed with diabetes; check-ups then belong with your own care provider.
• You are pregnant. Blood sugar monitoring in pregnancy runs through your midwife or gynaecologist.

You can bring a Bloodworks result into any of those conversations.

• 1Choose your test. The blood sugar test measures fasting glucose and HbA1c in one draw. If you want to place your blood sugar in a broader picture, there are packages that also look at cholesterol, liver and kidney values and the thyroid.
• 2Pay and complete the short intake. Our doctor assesses your request. Mention medicines, including diabetes medication, and any pregnancy; this is taken into account when your result is assessed. After approval you receive your lab form digitally.
• 3Have your blood drawn. You choose one of the affiliated collection sites across the Netherlands; at most of them you can walk in without an appointment. Come fasted: at least eight hours without food or drink, water excepted. Read beforehand how fasting blood tests work.
• 4The laboratory analyses your blood. Your blood goes to a certified Dutch laboratory, which sets your values against its own reference range.
• 5You receive your report with a doctor's interpretation. Your personal report is usually ready within two working days of the draw. A BIG-registered doctor explains your values in plain language and advises on any next step. If a value deviates strongly, we contact you.

An abnormal value is not a diagnosis. The diagnosis of diabetes is made by a doctor, usually only after a repeat measurement on another day and always in combination with your symptoms and health. A single elevated glucose can also have another explanation, for example that you were not fully fasted at the time of the draw.

A normal result is reassuring, but not a free pass: the risk of type 2 diabetes changes with the years, your weight and your lifestyle. If risk factors remain, measuring your blood sugar again later is a logical next step.

A few situations in which our doctor weighs your result differently, and which you should therefore mention in the intake:

• Medication: diabetes medication lowers glucose and HbA1c; corticosteroids and some other medicines can raise glucose.
• Illness and stress: fever, an infection or acute tension can push glucose up temporarily.
• Anaemia or an abnormal haemoglobin: HbA1c can then come out too high or too low, and the glucose value says more.
• Pregnancy: metabolism changes and monitoring runs through your midwife or gynaecologist.
• Not fully fasted: a snack or a sweet drink shortly before the draw raises glucose, not HbA1c.

If a value is elevated, repeating it on another day is the usual next step; our doctor indicates in the report when that is worthwhile. Do not compare your result with a number from the internet, but with the reference value in your report.

HbA1c is an average over weeks and therefore moves slowly with what you change structurally. The Dutch Diabetes Fund, Thuisarts.nl and the Netherlands Nutrition Centre name the same recognised lifestyle factors that favourably influence blood sugar and reduce the chance of type 2 diabetes:

• Exercise: half an hour of movement every day lowers blood sugar and reduces the chance of type 2 diabetes. Walking, cycling and taking the stairs count; choose something you will keep up.
• Weight: overweight, especially around the belly, makes the body less sensitive to insulin. The chance of diabetes already falls with a modest weight loss of a few kilos.
• Food and drink: wholegrain products instead of white flour, vegetables and fruit every day, pulses and nuts, and water, tea or coffee without sugar instead of soft drinks and fruit juice. The Dutch Wheel of Five is the basis for this.
• Not smoking: smoking makes the body less sensitive to insulin and clearly increases the chance of type 2 diabetes.
• Limiting alcohol and getting enough sleep and relaxation.

These are general recommendations, not treatment. If you take diabetes medication, never change the dose yourself on the basis of a result; that is done in consultation with your care provider. If you want to follow the effect of a changed lifestyle, a repeat measurement is only worthwhile after a few months.