Fasting glucose: what impaired fasting glucose means

Fasting glucose is one of the oldest and simplest blood tests there is. After a night without food, your body should keep blood sugar within a fairly tight band. When that control starts to slip, the fasting number is often one of the first things to show it.

What the test measures

Glucose is the main sugar in your blood and the fuel most of your cells run on. Overnight, your liver releases a steady trickle of glucose to keep you going, and insulin keeps that release in check. A fasting glucose measures how well this balance holds when no food is coming in.

For the result to mean anything, you need to have fasted for 8 to 12 hours. Water is fine. Coffee with milk and sugar, juice or a late snack can all push the number up and make a healthy result look abnormal.

The ranges LifePrint uses

LifePrint follows the SEMDSA 2017 guideline, which endorses the World Health Organization (WHO) criteria. Results are in mmol/L, the unit South African labs use:

• Below 6.1 mmol/L: normal.
• 6.1 to 6.9 mmol/L: impaired fasting glucose. LifePrint shows this as a grey zone.
• 7.0 mmol/L or more: in the diabetes range, which needs confirming on a separate day.

You may see a lower threshold of 5.6 mmol/L on American websites. That is the American Diabetes Association's cut-off. SEMDSA keeps the WHO value of 6.1 mmol/L, and LifePrint does the same, so your result matches what your South African doctor will use.

What impaired fasting glucose means

Impaired fasting glucose, often shortened to IFG, means your liver is releasing a little more sugar overnight than your insulin can fully control. It is one of the two main forms of prediabetes, along with an HbA1c of 6.0 to 6.4%.

It is not diabetes, and it does not cause symptoms. But it does mean your risk of developing type 2 diabetes over the coming years is higher than average. It is also linked to a higher risk of heart disease, which is why it is worth taking seriously even though you feel perfectly well.

Reading glucose alongside HbA1c

Fasting glucose and HbA1c answer slightly different questions. Glucose is a snapshot of this morning. HbA1c is an average over about three months. The Diabetes Check includes both because together they give a clearer answer than either alone.

• Both normal: reassuring.
• Glucose in the grey zone, HbA1c normal: often an early sign, or an effect of the day. A repeat is sensible.
• Both in the at-risk range: stronger evidence of prediabetes, and worth acting on.
• Either in the diabetes range: see a doctor to confirm and plan next steps.

When results disagree, a doctor may suggest an oral glucose tolerance test. You drink a measured sugar solution and have your glucose checked two hours later. It is the most sensitive way to see how your body handles a sugar load, and it can pick up problems that a fasting test misses.

When low glucose matters

A fasting glucose that is very low is uncommon in people who do not have diabetes. LifePrint treats a result below 2.8 mmol/L, or above 20 mmol/L, as a critical value that needs prompt medical attention. Your report will say so clearly. Mildly low results in a healthy person are usually harmless, but they are worth mentioning to your doctor if you also get shaky, sweaty or confused spells.

What to do with an IFG result

Impaired fasting glucose is a warning with time attached. For many people, steady changes to eating, activity, sleep and weight bring the number back into the normal range. A repeat test in three to twelve months, as your doctor suggests, shows whether it is working.

Your LifePrint report will explain your result and how urgently to follow up. A grey zone result is routine. A result in the diabetes range means you should see a registered healthcare practitioner soon. This is health information, not a diagnosis.