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Symptoms of Prediabetes (Borderline Diabetes)

Prediabetes is where an individual's blood sugar levels are higher than normal, but not enough to be diagnosed with type 2 diabetes. It is also known as borderline diabetes or impaired fasting glycaemia.1
Prediabetes is reversible with certain changes, such as increased exercise, a healthy diet, and certain medications. But without action, both adults and young children with prediabetes could be at long-term risk of health complications. 2
What are the symptoms of prediabetes?
Prediabetes comes usually without physical prediabetic symptoms1. If there are symptoms the prediabetes is already on the verge to manifest as diabetes. These can include the following symptoms1,3,4 :
  • Skin discolouration (acanthosis nigricans), particularly around the neck, armpits and groin
  • Tiredness and lethargy
  • Weight loss
  • Blurred vision
  • Going to the toilet more often (as excess glucose is excreted into your urine), which leads to dehydration
  • Increased thirst and/or hunger.
If any of the above symptoms occur, or you believe your blood glucose levels are too high or too low, speak with your family doctor as soon as possible.
Early signs are a blood sugar level that falls between 6.11mmol/L-6.94mmol/L* – a normal blood glucose level typically ranges between 4.4 - 6 mmol/L*,3,5 and an HbA1c between 6.0 and 6.4% (a normal HbA1c is < 6.0%) 1.
  • View our blood glucose charts and figures

What are the causes of prediabetes?

Prediabetes usually occurs in people who already have insulin resistance6. Insulin is the hormone that helps to move glucose out of your bloodstream and into your cells for energy – lowering your blood sugar levels following a meal and helping to keep you healthy.
The glucose metabolism in humans is a fine-tuned machine and one of the key players is the pancreas, releasing insulin among other hormones. Without its activity, glucose remains in the bloodstream. Due to various reasons tissues can start losing sensitivity towards insulin, resulting in a so called insulin resistance 7. As a compensation, the pancreas creates more insulin.5 Although this initially results in stable blood sugar levels, the pancreas can not maintain this increased secretion of insulin long-term and will become less efficient. With insulin-resistant tissues and less insulin released, excessive levels of glucose remain in the bloodstream, leading to high blood sugar levels which can be revealed in a blood test.
It is unclear why cells can become insulin resistant, but it is believed that excess weight and a lack of physical activity can be two major factors. Additional causes of prediabetes can include the use of certain medications, hormonal disorders (such as Cushing's syndrome6), or even sleep apnoea.8 A further complication of insulin resistance is metabolic syndrome, which is seen in individuals who encompass several conditions next to the impaired glucose metabolism, including excess weight, high blood pressure and high cholesterol levels, all of which can increase the risk of prediabetes.6

Risks of prediabetes

There is no one clear cause of prediabetes, several factors can place you at increased risk of developing an insulin resistance and becoming borderline diabetic, including genetics and lifestyle 6,10,11,12,13
  • Age: those who are over 45 years
  • Family history: having a parent or sibling with type 2 diabetes
  • Race and ethnicity: prediabetes occurs at higher rates in people who are of Asian, African-Caribbean or black African descent.
  • Carrying extra weight, especially around the middle
  • A sedentary lifestyle; lack of physical activity
  • An unhealthy diet with high fat, high GI, high refined carbohydrates, low fibre, few fruits and vegetables
  • Smoking, which is associated to increases insulin resistance
  • Certain medical conditions, such as polycystic ovary syndrome
  • Having gestational diabetes4 or giving birth to a baby over nine pounds.

Long-term complications if prediabetes is left untreated

If left untreated, prediabetes likely develops into type 2 diabetes and may cause significant long-term damages – up to 37% of individuals with prediabetes acquire diabetes within four years.2 However, implementing lifestyle changes can reduce the risk of diabetes to just 20%.2
If no treatment or lifestyle changes are made, long-term complications of diabetes can include the following 4,10,15:
  • Heart disease
  • High blood pressure
  • High cholesterol
  • Kidney disease
  • Nerve damage (peripheral neuropathy)
  • Fatty liver disease
  • Damage of peripheral blood vessels
  • Vision loss
  • Stroke
  • Foot problems, which can lead to amputation (due to nerve and blood vessel damage)
  • Hearing loss (due to nerve damage).
How is prediabetes diagnosed?
If you have any concerns about prediabetes or have any of the above symptoms, visit your family doctor to complete a prediabetes diagnosis test. Three key blood sugar blood tests can be used to identify prediabetes. These are the A1C test, which is non-fasting, the fasting plasma glucose (FMG) test, and the glucose tolerance test.15 Your family doctor will inform you which prediabetes diagnosis test is the right one for you.

Haemoglobin HbA1c test

The haemoglobin HbA1c test (also known as the prediabetes HbA1C blood test) is one of the most common tests for prediabetes and diabetes. It is a non-fasting test that can be undertaken at any time of day – results are unaffected by physical activity at the day of testing, unlike the Fasting Plasma Glucose or Oral Glucose Test.17,18
The HbA1c test measures the fraction of haemoglobin (the protein that carries oxygen in you blood through your body) in your red blood cells that has sugar attached and is a good biomarker for your average blood sugar level for the previous two to three months. The higher your HbA1c result the higher your average blood sugar level.16 The test can be completed by your family doctor, who will take a sample of blood from your finger or your arm for testing.
A normal HbA1c test result will be below 5.7%, whereas one that ranges between 6.0% to 6.4% indicates that an individual has prediabetes.16 A result above 6.5% signals diabetes.18 Check with your GP to test alongside an alternative test to confirm the diagnosis.19,20
Fasting plasma glucose (FPG) test
The fasting plasma glucose (FPG) test will be completed with your family doctor or a hospital specialist in the morning following an 8-10 hour fasting period (before breakfast) to successfully measure blood glucose levels.17
A normal FPG test result will be less than 5.5 mmol/l, but those with prediabetes will have impaired fasting glucose levels between 5.6 – 6.9 mmol/l. If results exceed 7.9 mmol/l, it suggests diabetes. The FPG test is quick and easy, but the test will need to be completed twice, or combined with an alternative test to confirm a diagnosis. 17
However, the test will be unable to decipher the types of diabetes, or whether raised blood glucose levels have resulted from other factors, such as medications or stress.20
Glucose tolerance test
The glucose tolerance test (or oral glucose tolerance test) is often used to help determine whether an individual has prediabetes, insulin resistance, reactive hypoglycaemia, or gestational diabetes by measuring sugar intake.18 Individuals will need to fast overnight, for 8 - 12 hours, before completing this test. During the test, a healthcare professional will take some blood to measure your blood glucose levels. Following this, you will be asked to consume a standardised glucose drink. You will then have your blood glucose levels measured at several intervals, from 30 minutes to every hour, for up to three hours.
For those without diabetes, blood glucose levels will usually be under 6.0 mmol/L following an overnight fasting period, rising to not more than 7.8 mmol/L within two hours after the sugary glucose drink has been consumed.14,18 For those with prediabetes (or impaired glucose intolerance), blood glucose levels before the test will be between 6.0 - 7.0mmol/L rising to 7.9 – 11.0 mmol/L after the drink. 18 If blood glucose levels are over 7.0 mmol/L following an overnight fast or are more than 11.0 mmol/L after two hours after consuming a sugary drink, it could indicate that an individual has diabetes.18

How to prevent prediabetes

Healthy lifestyle choices can help to prevent the risk of developing prediabetes and type 2 diabetes. While the key goal for prediabetes treatment should be to normalise blood glucose levels, this will incorporate steps such as losing some weight and increasing physical activity.1
Adopting a low carbohydrate diet that is rich in fibre, whole grains, nuts and seeds and fruits and vegetables, and removing or reducing sweet or sugary foods can help to lower your blood glucose levels, regulate your blood pressure and cholesterol levels and lower the risk of developing prediabetes. 22,23 Quitting smoking can also lower the risk of insulin resistance and can work towards prediabetes prevention. 11
* Measurement has been converted from mg/dL to mmol/L. Blood Sugar Converter, Diabetes.co.uk. Last reviewed on June 10, 2022
1 Diabetes UK. Prediabetes. . Accessed on 29 November 2022. Diabetes UK.
2 Tuso P. Prediabetes and lifestyle modification: time to prevent a preventable disease. Perm J 2014 Summer;18(3):88-93. NIH.
3 Alvarez S et al. Prediabetes. Published January 2022. Updated 18 July 2022. StatPearls [Internet]. NIH;
4 Mayo Clinic, Prediabetes. Mayo Clinic .2022. Accessed on 29 November 2022.
5 Mathew TK et al. Blood Glucose Monitoring. Updated 8 August 2022. In: StatPearls [Internet]. NIH.
6 NIH. Insulin Resistance & Prediabetes. Updated May 2018. Accessed 27 January 2023. NIH.
7 James DE, et al. The aetiology and molecular landscape of insulin resistance. Nature Reviews Molecular Cell Biology. 2021;22:751-771.
8 Munir A, et al. Management of diabetes mellitus in Cushing's syndrome. 2010;92 Suppl 1:82-5. NIH.
9 Mokhlesi B, et al; RISE Consortium. Obstructive Sleep Apnea, Glucose Tolerance, and β-Cell Function in Adults With Prediabetes or Untreated Type 2 Diabetes in the Restoring Insulin Secretion (RISE) Study. 2021 Apr;44(4):993-1001. NIH.
10 Centers for Disease Control and Prevention. About Prediabetes and Type 2 Diabetes.. Published 2019. Updated Reviewed October 2022. Update accessed date to 4th September. CDC.
11 National Health Service. Symptoms Type 2 diabetes. Published 2018. Updated18 August 2020. Accessed on 29 November 2022. NHS.
12 Artese A, et al. Cigarette Smoking: An Accessory to the Development of Insulin Resistance. 2017 Aug 23;13(6):602-605. Am J Lifestyle Med.
13 Centers for Disease Control and Prevention. PCOS (Polycystic Ovary Syndrome) and Diabetes. Published 2020. Update accessed date to 4th September. CDC.
14 Centers for Disease Control and Prevention, Diabetes and Hearing Loss. Published 2021 . Updated 27 May 2022. Update accessed date to 4th September. CDC.
15 National Institute of Diabetes and Digestive and Kidney Diseases, Recommended Tests for Identifying Prediabetes. Published 2020. Accessed on 29 November 2022. NIDDK.
16 Diabetes UK. Prediabetes. Accessed 27 January 2023. Diabetes UK.
17 Diabetes.co.uk, Fasting Plasma Glucose Test. Published 2019. Updated June 10 2022. Accessed on 29 November 2022. Diabetes.co.uk.
18 Diabetes.co.uk, Oral Glucose Tolerance Test. Published 2019. Updated June 10 2022. Accessed on 29 November 2022. Diabetes.co.uk.
19 National Institute of Diabetes and Digestive and Kidney Diseases, The A1C Test & Diabetes. Published 2018. Accessed on 29 November 2022. NIDDK.
20 National Institute of Diabetes and Digestive and Kidney Diseases, Diabetes and Prediabetes Tests. Published 2020. Updated August 2020. Accessed on 29 November 2022. NIDDK.
21 Centers for Disease Control and Prevention. Prediabetes – Your Chance to Prevent Type 2 Diabetes. Published 2014. Updated 21 December 2021. Update accessed date to 4th September. CDC.
22 Bolla AM, et al. Low-Carb and Ketogenic Diets in Type 1 and Type 2 Diabetes. Nutrients. 2019 Apr 26;11(5):962. NIH.
23 Diabetes UK. 10 tips for healthy eating if you are at risk of type 2 diabetes. Accessed 27 January 2023. Diabetes UK.
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