High fasting blood sugar: do I have diabetes or not?

High fasting blood sugar: do I have diabetes?

You had your blood test in the morning, and your glucose came out at 105, 112 or 120 mg/dL. On the report it's in red or has an asterisk. The first question is simple: do I have diabetes?

A single result between 100 and 125 mg/dL doesn't mean diabetes. It means your blood sugar is higher than normal and it's worth finding out why. The US National Institute of Diabetes (NIDDK) says your doctor will usually use a second test to confirm a diagnosis.

Fasting blood glucose measures the sugar in your blood at one moment, after at least 8 hours without food or drinks other than water. The value can change from one day to the next. That's why a result means more when it's put next to others.

What does your result mean, by range?

Test	Normal	Prediabetes	Diabetes
Fasting blood glucose	99 mg/dL or below	100–125 mg/dL	126 mg/dL or above
HbA1c	below 5.7%	5.7–6.4%	6.5% or above
Glucose 2 hours into a glucose tolerance test	139 mg/dL or below	140–199 mg/dL	200 mg/dL or above

These are the American Diabetes Association's thresholds, also used by NIDDK. The World Health Organization sets the threshold for "impaired fasting glucose" at 110 mg/dL, not 100. This is also why the reference range on your report differs from one lab to another. In the UK, results are given in mmol/L: 100 mg/dL is about 5.6 mmol/L and 126 mg/dL is 7.0 mmol/L.

Back to the question at the start: a fasting glucose of 105–120 mg/dL falls in the prediabetes range by the American thresholds. Diabetes is discussed from 126 mg/dL upwards, confirmed by a second test.

Why can fasting blood sugar come out high without it being diabetes?

Morning blood sugar is sensitive to what happened the day or night before. It can come out higher than usual for you if:

• you weren't really fasting: a coffee with sugar or milk, a juice, a late snack after midnight;
• you slept badly or very little;
• you're stressed, including by the trip to the lab or a fear of needles;
• you have a cold or an infection;
• you take certain medicines, such as steroids;
• you have a thyroid problem. MedlinePlus lists an overactive thyroid among the causes of high blood glucose.

That doesn't mean the value is wrong. It means one test isn't enough to draw a conclusion, either good or bad.

Why is the test repeated, and how does it link to HbA1c?

For a diagnosis, the American Diabetes Association asks for two results above the threshold. They can come from the same test repeated or from two different tests. The exception is someone with clear symptoms and a very high blood sugar.

The most common second test is HbA1c. It shows your average blood sugar over roughly the last three months, so one bad night or a late dinner won't spoil it. If your glucose is 112 mg/dL and your HbA1c is 5.4%, the picture looks different than if your HbA1c is 6.1%.

Sometimes your doctor asks for a glucose tolerance test: you drink a sugary solution and your blood sugar is measured again two hours later. The test shows how your body copes with a load of sugar.

What can you do from tomorrow about high fasting blood sugar?

Prediabetes doesn't usually cause symptoms, but it's the point where changing habits has the biggest effect. The NHS says exercise, a healthy weight and meals with less sugar and more fibre can delay or prevent type 2 diabetes.

What you do	Why it helps
Walk for 10–15 minutes after your main meal	your muscles use the glucose in your blood
Cut out fizzy drinks and sweetened drinks	liquid sugar raises blood sugar quickly and doesn't fill you up
Fill half your plate with vegetables	fibre slows the rise in blood sugar after a meal
Choose wholegrain bread and pasta	they're digested more slowly than white ones
Sleep 7–9 hours, at regular times	short sleep makes your body less sensitive to insulin
Lose a few kilos, if you're carrying extra weight	even a small loss improves blood sugar

Pick two things you can keep up. You don't need a strict diet. What counts is doing them every day, for months.

To repeat the test properly, fast for at least 8 hours, with water only. Don't change anything special the day before, either for better or worse. You want to see your usual blood sugar, not the blood sugar after a day of fasting or a big dinner.

How does MentorSano help when you have high fasting blood sugar?

MentorSano doesn't diagnose. It helps you put your blood sugar next to your other results and your habits, so you know what to ask your doctor and what to change before the next test.

• You upload your blood tests and your glucose and HbA1c appear on the same chart, report after report. You see whether the value is going up, staying put or coming down.
• After the 15-minute questionnaire you get your list of recommended tests. You find out which are worth repeating and which your GP may be able to order.
• The daily journal and the daily to-do keep track of your sleep, steps and habits such as a walk after meals, in a minute or two a day.
• With the subscription, AI reads your results together with your answers and journal, and Adrian Ienin, a pharmacist, checks the "What matters now" plan. You also get a menu for the week, to your taste and schedule.

To see your blood sugar on a chart, create your free MentorSano account. Uploading your results, the questionnaire and the journal are free.

What should you ask your GP?

Take your new report to the appointment and, if you have them, your old results too. A few useful questions:

• "Does my result mean prediabetes, or does it need confirming?"
• "Should I also have an HbA1c test?"
• "When should I repeat the test?"
• "Can the medicines I take raise my blood sugar?"

Also tell them if diabetes runs in your family, if you had diabetes in pregnancy or if you have high blood pressure. All of these change how often your blood sugar is worth checking.