METABOLIC HEALTH
Pre-Diabetes Blood Test UK: How to Catch Insulin Resistance Before It Becomes Type 2
An estimated 5.1 million people in England have blood sugar levels in the pre-diabetic range — and most of them have no idea. Pre-diabetes rarely causes symptoms. There is no pain, no thirst, no visible warning. The only reliable way to catch it is a blood test.
The good news: pre-diabetes is reversible. The landmark NHS Diabetes Prevention Programme showed that lifestyle changes can cut the risk of progressing to type 2 diabetes by up to 58%. But you can only act on what you can measure. This guide explains which blood tests matter, what the numbers mean, and why the standard NHS check may not be enough.
What is pre-diabetes?
Pre-diabetes — sometimes called “non-diabetic hyperglycaemia” or “impaired glucose regulation” — means your blood sugar is higher than normal but not yet high enough for a type 2 diabetes diagnosis. The NICE PH38 guideline defines it as an HbA1c between 42 and 47 mmol/mol (6.0–6.4%), or a fasting plasma glucose between 5.5 and 6.9 mmol/L.
The clinical reality is less binary than those thresholds suggest. Insulin resistance — the underlying driver of most type 2 diabetes — begins years before HbA1c crosses the 42 mmol/mol line. Your pancreas compensates by producing more insulin, keeping glucose in range while your metabolic health is quietly deteriorating. By the time HbA1c is flagged, the horse has often bolted.
This is why a comprehensive metabolic blood panel matters. A single HbA1c reading tells you where you are on the spectrum. A panel that includes fasting insulin and HOMA-IR tells you how fast you are moving along it.
Who is at risk?
The NICE NG28 guideline on type 2 diabetes prevention identifies the following risk factors. Having even one should prompt a blood test:
Critically, many people with pre-diabetes have none of the “classic” risk factors. A 2020 BMJ analysis found that approximately 1 in 3 UK adults aged 45–54 with a normal BMI still had HbA1c in the pre-diabetic range. Body weight alone is not a reliable screening criterion.
1. HbA1c (glycated haemoglobin)
HbA1c measures the percentage of haemoglobin in your red blood cells that has glucose attached to it. Because red blood cells live for about 120 days, HbA1c gives you a rolling 2–3 month average of your blood sugar control — not just a snapshot on the day of the test.
The WHO and NICE use the following thresholds:
| Category | HbA1c (mmol/mol) | HbA1c (%) |
|---|---|---|
| Normal | Below 42 | Below 6.0% |
| Pre-diabetes | 42–47 | 6.0–6.4% |
| Type 2 diabetes | 48 or above | 6.5% or above |
The problem: an HbA1c of 41 mmol/mol is classified as “normal” but sits one point below the pre-diabetes threshold. For someone trending upward from 36 to 41 over three years, this is not reassuring — it is an early warning that the standard system may not flag.
Optimal range for metabolic health: below 36 mmol/mol (5.4%). If yours is between 36 and 41, you are not pre-diabetic by NHS criteria, but your metabolic trajectory deserves attention — particularly if combined with elevated fasting insulin or triglycerides. See our complete HbA1c guide for a deeper dive.
2. Fasting glucose
Fasting plasma glucose (FPG) measures the concentration of glucose in your blood after an overnight fast of at least 8 hours. Unlike HbA1c, it is a point-in-time measurement that can fluctuate with stress, illness and what you ate the night before.
NICE defines impaired fasting glucose (IFG) as 5.5–6.9 mmol/L. A reading of 7.0 mmol/L or above on two separate occasions indicates type 2 diabetes. Below 5.5 is considered normal.
The limitation: fasting glucose is a lagging indicator. Your pancreas works hard to keep fasting glucose within range even when insulin resistance is advancing. A person can have significant insulin resistance for years while maintaining a normal fasting glucose. This is why fasting glucose alone is insufficient — you need to pair it with fasting insulin to see the full picture.
Optimal range: 4.0–5.0 mmol/L. If your fasting glucose is consistently above 5.0 but below the NHS 5.5 threshold, investigate further with fasting insulin and HOMA-IR.
3. Fasting insulin
This is the marker that changes the game. Fasting insulin measures how much insulin your pancreas is producing to keep your blood sugar in range. It is the earliest detectable sign of insulin resistance — often elevated 10–15 years before HbA1c crosses the pre-diabetic threshold.
The Whitehall II cohort study (published in The Lancet Diabetes & Endocrinology, 2016) tracked 6,538 UK civil servants and found that fasting insulin begins to rise significantly 13 years before a type 2 diabetes diagnosis. By the time HbA1c is flagged, insulin levels have often been abnormally high for over a decade.
The NHS does not routinely test fasting insulin. It is not part of the NHS Health Check or the standard GP diabetes screen. This is arguably the single biggest gap in UK metabolic screening. You will almost certainly need to request it privately. See our fasting insulin biomarker page for reference ranges and clinical context.
Optimal range: 20–60 pmol/L (or roughly 3–8 mIU/L in older units). Above 60 pmol/L suggests early insulin resistance even if glucose and HbA1c are normal. Above 100 pmol/L warrants serious investigation.
4. HOMA-IR (insulin resistance score)
HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is a calculated index derived from your fasting glucose and fasting insulin values. The formula is simple:
HOMA-IR = (fasting insulin × fasting glucose) ÷ 22.5
Using mIU/L for insulin and mmol/L for glucose
A HOMA-IR below 1.0 indicates excellent insulin sensitivity. Between 1.0 and 1.9 is considered normal. A score of 2.0 or above suggests early insulin resistance. Above 2.9 is consistent with significant insulin resistance.
The value of HOMA-IR is that it captures the relationship between insulin and glucose, not just the absolute levels. A person with a fasting glucose of 5.2 mmol/L and a fasting insulin of 12 mIU/L has a very different metabolic picture from someone with the same glucose but insulin at 25 mIU/L — even though both would have a “normal” glucose on an NHS screen.
Optimal: below 1.5. This is where you want to be for long-term metabolic health. If your HOMA-IR is between 1.5 and 2.5 with no other risk factors, targeted lifestyle changes (see the interventions section) are usually sufficient to reverse it.
5. Triglycerides and the TG:HDL ratio
Triglycerides are the main form of fat circulating in your blood. Elevated triglycerides are strongly associated with insulin resistance — they are a downstream consequence of the same metabolic dysfunction. The NICE CG181 lipid modification guideline considers fasting triglycerides above 1.7 mmol/L elevated.
More useful than triglycerides alone is the triglyceride-to-HDL ratio (TG:HDL). Research published in Circulation (2003) and confirmed in subsequent studies found that a TG:HDL ratio above 1.3 (in mmol/L units) correlates strongly with insulin resistance — in some populations, as reliably as a formal glucose tolerance test.
If you already have a standard lipid panel from your GP, divide your triglycerides by your HDL. A ratio below 0.9 is excellent. Between 0.9 and 1.3 is normal. Above 1.3 warrants investigation of insulin resistance. Above 2.0 is a strong signal. See our cholesterol blood test guide for more on lipid interpretation.
Optimal triglycerides: below 1.0 mmol/L. Optimal TG:HDL: below 0.9.
6. Vitamin D and metabolic risk
The link between vitamin D deficiency and type 2 diabetes has been accumulating for over a decade. A landmark 2023 NEJM trial (D2d) found that vitamin D supplementation (4,000 IU/day) reduced the risk of progression from pre-diabetes to type 2 by 76% in participants who achieved blood levels above 125 nmol/L — and by 62% overall in the vitamin D group versus placebo in a secondary analysis of those with vitamin D deficiency at baseline.
Vitamin D appears to improve beta-cell function (the pancreatic cells that produce insulin) and reduce systemic inflammation — both relevant to insulin resistance. The NHS recommends supplementation for all UK adults in autumn and winter, but their threshold for “sufficient” (above 25 nmol/L) is far below the level associated with metabolic protection.
Optimal range for metabolic health: 75–125 nmol/L. If you have pre-diabetes and your vitamin D is below 50 nmol/L, correcting this is one of the cheapest and best-evidenced interventions available. See our vitamin D deficiency guide.
NHS vs optimal ranges for pre-diabetes screening
| Marker | NHS “normal” | Optimal | Concern |
|---|---|---|---|
| HbA1c | Below 42 mmol/mol | Below 36 mmol/mol | 36–41 — trending |
| Fasting glucose | Below 5.5 mmol/L | 4.0–5.0 mmol/L | 5.0–5.5 — investigate |
| Fasting insulin | Not routinely tested | 20–60 pmol/L | Above 60 pmol/L |
| HOMA-IR | Not routinely tested | Below 1.5 | Above 2.0 |
| Triglycerides | Below 1.7 mmol/L | Below 1.0 mmol/L | Above 1.7 mmol/L |
| TG:HDL ratio | Not reported | Below 0.9 | Above 1.3 |
| Vitamin D | Above 25 nmol/L | 75–125 nmol/L | Below 50 nmol/L |
Sources: NICE NG28, WHO HbA1c diagnostic criteria, NICE CG181 lipid modification, NHS vitamin D guidance. Optimal ranges reflect longevity-medicine consensus (not NHS diagnostic thresholds).
What the NHS Health Check misses
The NHS Health Check, offered to adults aged 40–74 every five years, is a good starting point. But for pre-diabetes detection, it has significant blind spots:
No fasting insulin
The Health Check uses HbA1c or fasting glucose alone. This means insulin resistance can progress silently for years while glucose remains in range. The earliest and most actionable marker — fasting insulin — is not tested.
No HOMA-IR calculation
Without fasting insulin, HOMA-IR cannot be calculated. This eliminates the most reliable non-invasive measure of insulin resistance.
TG:HDL ratio not reported
Triglycerides and HDL are tested as part of the lipid panel, but the TG:HDL ratio — a strong surrogate for insulin resistance — is rarely calculated or discussed.
5-year interval
Pre-diabetes can develop and progress to type 2 within 3–5 years. A 5-year screening interval may miss the entire pre-diabetic window, especially for high-risk individuals. Annual testing is more appropriate for those with risk factors.
Conservative thresholds
The NHS flags HbA1c at 42 mmol/mol. An HbA1c of 39–41 is classified as normal, but represents a trajectory toward pre-diabetes that would benefit from early intervention.
This is not a criticism of the NHS — the Health Check was designed as a population-level screening tool with resource constraints. But if you have risk factors for pre-diabetes, or you simply want to know your metabolic trajectory rather than just your current category, a private blood test that includes fasting insulin and HOMA-IR provides significantly more information. See our NHS vs private blood test comparison.
GP vs Helvy for pre-diabetes screening
| NHS GP | Helvy | |
|---|---|---|
| HbA1c | Yes | Yes |
| Fasting glucose | Yes (if requested) | Yes |
| Fasting insulin | Rarely (specialist referral only) | Yes |
| HOMA-IR | Not calculated | Yes (auto-calculated) |
| Triglycerides + TG:HDL | Triglycerides yes, ratio not reported | Both reported |
| Vitamin D | Only if symptomatic | Yes |
| Cholesterol + ApoB | Standard lipids (no ApoB) | Full panel including ApoB |
| Turnaround | 2–4 weeks | 5 working days |
| GP referral required? | No (NHS Health Check) / Yes (insulin) | No |
| Optimal range reporting | No — normal/abnormal only | Yes — with clinical context |
4 pre-diabetes result patterns
These are the most common patterns we see. Yours may not fit neatly into one category — always discuss your results with a healthcare professional.
Pattern 1: Early insulin resistance (the silent phase)
Markers: Normal HbA1c, normal fasting glucose, elevated fasting insulin (above 60 pmol/L), HOMA-IR above 2.0
Your pancreas is working overtime to keep glucose in range. You would pass every standard NHS screen. This is the most important pattern to catch because it is entirely reversible with lifestyle changes and the intervention window is at its widest.
Action: Lifestyle intervention (see below). Retest in 3 months.
Pattern 2: Metabolic syndrome picture
Markers: TG:HDL above 1.3, fasting insulin elevated, HbA1c 36–41, waist circumference above threshold
Insulin resistance is affecting lipid metabolism as well as glucose. You may also have elevated blood pressure and low-grade inflammation. This is the classic metabolic syndrome pattern described in the IDF consensus definition.
Action: Urgent lifestyle intervention. Consider GP review for cardiovascular risk assessment. If HbA1c is 39–41, retest in 3 months rather than waiting for the 5-year NHS interval.
Pattern 3: Established pre-diabetes
Markers: HbA1c 42–47, fasting glucose 5.5–6.9, elevated insulin, HOMA-IR above 2.5
You are in the NICE-defined pre-diabetes range. The good news: the Diabetes Prevention Programme evidence shows this is still highly reversible. The bad news: the clock is running — without intervention, 5–10% of people with pre-diabetes progress to type 2 each year.
Action: NHS Diabetes Prevention Programme referral (your GP can refer you). Concurrent private monitoring every 3 months to track response to intervention.
Pattern 4: Vitamin D-compounded risk
Markers: Any of the above patterns + vitamin D below 50 nmol/L
Vitamin D deficiency is adding to your metabolic risk. The D2d trial showed that correcting deficiency can significantly reduce progression risk — this is low-hanging fruit.
Action: Vitamin D3 supplementation (2,000–4,000 IU/day), targeting blood level above 75 nmol/L. Retest in 8 weeks.
Evidence-based interventions for pre-diabetes
The evidence for reversing pre-diabetes through lifestyle change is among the strongest in all of medicine. Here are the interventions ranked by effect size:
Weight loss (5–10% of body weight)
58% reduction in type 2 riskThe Diabetes Prevention Programme — the largest trial of its kind, 3,234 participants — found that losing 7% of body weight through diet and exercise reduced progression to type 2 by 58%. This was more effective than metformin (31% reduction). Even modest weight loss of 5% produces significant improvement in insulin sensitivity.
Source: DPP / NICE NG28
Resistance training (2–3 sessions/week)
Improves insulin sensitivity by 20–40%Muscle is the largest insulin-sensitive tissue in the body. Each kilogram of muscle gained increases glucose disposal capacity. Resistance training improves insulin sensitivity independently of weight loss — even without losing a single pound.
Source: Sports Medicine 2020 meta-analysis
Walking after meals (10–15 minutes)
Reduces post-meal glucose spikes by 30–50%A 2022 meta-analysis of 7 studies found that even a brief walk after eating significantly blunts the post-prandial glucose spike. The effect is immediate and does not require gym-level effort.
Source: Sports Medicine 2022 meta-analysis
Reduce refined carbohydrates
Reduces fasting insulin and triglyceridesReplacing refined carbohydrates with whole grains, vegetables and protein reduces the glycaemic load of meals, lowering both glucose and insulin spikes. This is not a zero-carb recommendation — it is about the quality and timing of carbohydrates.
Source: BMJ 2023 / NICE NG28
Sleep optimisation (7–9 hours)
1 week of 4h sleep increases insulin resistance by 30%Sleep deprivation is an independent and potent driver of insulin resistance. A study by Broussard et al. found that restricting healthy young men to 4 hours of sleep for just 4 nights increased their adipocyte insulin resistance by 30%. Fixing sleep is a metabolic intervention.
Source: Annals of Internal Medicine 2012
Vitamin D correction (if deficient)
Up to 76% reduction in progression riskIn participants with baseline vitamin D below 30 nmol/L who achieved levels above 125 nmol/L, the D2d trial found a 76% relative risk reduction for progression to type 2. Even the overall effect (12% RRR) was clinically meaningful at population scale.
Source: NEJM D2d trial 2023
Metformin (prescription only)
31% reduction in type 2 riskNICE recommends considering metformin for people with pre-diabetes and additional risk factors (BMI above 35, rising HbA1c despite lifestyle changes, gestational diabetes history). It is less effective than intensive lifestyle intervention but more sustainable for some people. Discuss with your GP.
Source: DPP / NICE NG28
Frequently Asked Questions
Can pre-diabetes be reversed?
Yes. The Diabetes Prevention Programme found that lifestyle changes (modest weight loss, regular exercise, dietary improvement) reduced the risk of progressing to type 2 diabetes by 58%. Many people with pre-diabetes return to normal glucose regulation within 12–24 months of sustained intervention.
Will my GP test my fasting insulin?
Unlikely. Fasting insulin is not part of the standard NHS diabetes screen or the NHS Health Check. GPs can request it, but many are unfamiliar with interpreting it outside of a specialist endocrinology context. Private testing is the most reliable way to get this marker.
How often should I retest if I have pre-diabetes?
Every 3 months during active intervention, then every 6 months once you are in the optimal range. The NHS recommends annual HbA1c monitoring for people with pre-diabetes, but if you are making lifestyle changes, 3-monthly testing lets you see whether they are working before a full year has passed.
Does a normal BMI mean I can’t have pre-diabetes?
No. Approximately 1 in 3 UK adults with a normal BMI aged 45–54 has HbA1c in the pre-diabetic range. Visceral fat (fat around the organs), physical inactivity, poor sleep and genetic predisposition can all drive insulin resistance independently of total body weight.
What is the difference between pre-diabetes and type 2 diabetes?
Pre-diabetes means your blood sugar is elevated but below the diagnostic threshold for type 2 (HbA1c 42–47 mmol/mol). Type 2 diabetes is diagnosed at 48 mmol/mol or above. The distinction matters because pre-diabetes is reversible with lifestyle changes, while type 2 is manageable but rarely fully reversed once established.
Which Helvy panel should I choose for pre-diabetes screening?
The Essential panel (£129) includes HbA1c, fasting glucose, cholesterol, triglycerides and vitamin D. The Heart panel (£89) focuses on cardiovascular and metabolic markers including HbA1c, triglycerides, ApoB and hs-CRP. For the most comprehensive metabolic picture including fasting insulin, ask about custom marker add-ons when ordering.
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By Helvy · Medically reviewed