Your average blood sugar over three months — the test that identifies prediabetes while it's still reversible.
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HbA1c measures your average blood glucose over roughly the previous three months. Unlike a single glucose reading, it cannot be skewed by what you happened to eat that morning — which is why it is the standard test for diagnosing and monitoring type 2 diabetes.
The more useful thing this panel does is look earlier than that. Insulin resistance develops years before glucose starts to rise, and measuring insulin alongside HbA1c is what distinguishes catching the problem while it is still reversible from catching it once it has a name.
HbA1c — the proportion of your haemoglobin that has glucose attached. Because red cells live around three months, it reflects your average over that period.
The UK diagnostic thresholds are worth knowing: below 42 mmol/mol is normal, 42–47 is prediabetes, and 48 or above on two occasions indicates diabetes. Prediabetes is the band that matters most here, because it is the one where change still reverses the trajectory.
Glucose — the level at the moment of the sample.
Insulin and C-peptide — these are what standard testing omits and what makes this panel worth doing. Raised insulin with a normal glucose is insulin resistance: the body is working progressively harder to keep glucose normal, and succeeding, for now. That state can persist for years while every routine test comes back reassuring. C-peptide shows how much insulin your pancreas is producing itself.
One important caveat. HbA1c is unreliable in anyone with anaemia, a haemoglobin variant such as sickle cell or thalassaemia trait, recent significant blood loss, or advanced kidney disease — because it depends on red cells behaving normally. In those situations glucose testing is used instead, and we would say so rather than report a figure that cannot be trusted.
Included: HbA1c · glucose · insulin · C-peptide.
Measuring insulin and C-peptide alongside HbA1c shows insulin resistance, which develops years before blood sugar itself becomes abnormal. It is the difference between catching the problem early and catching it late.
1. Consultation. We establish the risk picture — family history, ethnicity, weight distribution and symptoms — which determines what is worth measuring and how the result should be read.
2. Referral. To a Randox Health clinic at a time that suits you. We usually request lipids, liver function and kidney function alongside, since metabolic problems rarely arrive alone.
3. The sample. A single blood draw. No fasting is needed for HbA1c itself — only if fasting glucose is being measured at the same time, which we will confirm beforehand.
4. Results review. A GP explains what the number means for you specifically. A result in the prediabetes range is the most actionable finding in this panel, and the conversation about what actually shifts it is worth more than the figure.
No fasting is required for HbA1c alone. Fast for 10 hours if fasting glucose is being measured at the same time.
HbA1c reflects your average blood sugar over roughly the previous three months, which is why a single bad week does not distort it.
It is the point at which the trajectory can still be changed, and roughly a third of people in that range go on to develop type 2 diabetes within a few years.
The NHS Diabetes Prevention Programme is free, and it genuinely reduces progression. A prediabetes result reported with no explanation and no referral is a wasted opportunity — and that happens constantly.
Insulin resistance develops years before blood sugar itself becomes abnormal. The body compensates by producing more insulin, and HbA1c stays normal throughout that period.
Measuring insulin and C-peptide alongside shows the compensation happening — which is the difference between catching this early and catching it late. It is not part of standard NHS testing.
It measures sugar attached to haemoglobin, so anything affecting red cell lifespan distorts it:
In those situations a fasting glucose or a glucose tolerance test is the better measure, and using HbA1c alone can genuinely mislead.
An average conceals variability. Someone with frequent high and low swings can produce a reassuring HbA1c, and the swings themselves matter.
Where that is a question, continuous glucose monitoring gives a picture HbA1c cannot.
Insulin resistance can be well established with a completely normal HbA1c, sometimes for years. If the question is metabolic risk rather than diagnosis, insulin and C-peptide are what answer it.
Getting a prediabetes result explained rather than filed. And insulin and C-peptide, which are not part of standard NHS testing and which show insulin resistance years before HbA1c moves.
It matters a great deal — it is the most useful result on this page. HbA1c of 42 to 47 means blood sugar is above normal but below the diabetes threshold.
It is a warning with the window still open, and roughly a third of people go on to develop diabetes within a few years. The NHS Diabetes Prevention Programme is free and genuinely reduces that.
Not for HbA1c alone — it can be taken at any time of day.
Fast for 10 hours if fasting glucose is being measured at the same time, which it usually is on a wider panel. Confirm at your consultation.
No more often than every three months, because that is how long red cells live and how far back the measurement reaches.
Testing monthly produces a number that cannot have meaningfully changed.
Yes, in specific situations. Anaemia, recent blood loss or transfusion, pregnancy, advanced kidney disease, and haemoglobin variants such as sickle cell trait or thalassaemia trait all distort it.
Those traits are common and frequently unknown to the person. Where any apply, fasting glucose or a glucose tolerance test is the better measure.
Frequently, yes — and that is the whole point of finding it.
Weight loss is the single most effective lever, along with activity and reducing refined carbohydrate. The free NHS programme is built around exactly this, and it works.
Yes, and it is a legitimate goal rather than wishful thinking — particularly within the first few years of diagnosis, and with substantial weight loss.
Remission is not cure, and it needs continued monitoring — but it is real, it is achievable for a meaningful proportion of people, and it is not offered often enough.
The state where your body needs progressively more insulin to keep blood sugar normal. It develops years before HbA1c becomes abnormal, because the compensation works — until it does not.
Measuring insulin and C-peptide shows that happening, which is the difference between catching it early and catching it late.
Worth taking seriously. Thirst, passing large volumes of urine, weight loss and blurred vision with a normal HbA1c can mean type 1 diabetes developing rapidly, which HbA1c is too slow to capture.
That is a same-day matter, not a routine one.
For diabetes, they are genuinely valuable. For a well person, we would say no.
Glucose rising after a meal is normal physiology, not a malfunction — and interpreting ordinary spikes as damage leads to unnecessary food restriction and real anxiety. They are marketed heavily to people who do not need them.
None has evidence approaching that of weight loss, activity and the free NHS prevention programme.
Berberine and cinnamon are the ones most often promoted; the evidence is weak, quality is unregulated, and berberine interacts with several prescription medicines.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 23, 2026
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