Prediabetes: What It Means, Why It Matters, and What To Do Next

Prediabetes means your blood glucose is higher than normal, but not yet high enough to be diagnosed as type 2 diabetes. It is a warning sign, not a disease, and with the right steps it can often be reversed. This guide explains what prediabetes means in a South African context, how it is diagnosed locally, and what to do if your doctor has told you your numbers are borderline.

What is prediabetes?

Prediabetes is a metabolic state in which blood glucose levels are elevated above normal but have not yet reached the threshold for type 2 diabetes. It represents a critical window for intervention, during which lifestyle changes can prevent or delay progression to diabetes.

The term encompasses two distinct conditions: impaired fasting glucose (IFG) and impaired glucose tolerance (IGT). IFG refers to elevated glucose levels after an overnight fast, whilst IGT describes an abnormal glucose response to a standard glucose load during an oral glucose tolerance test (OGTT). Some individuals have both conditions, which carries the highest risk of progression to diabetes.

In South Africa, the Society for Endocrinology, Metabolism and Diabetes of South Africa (SEMDSA) recommends using glucose-based measurements, specifically fasting plasma glucose or the OGTT, to diagnose prediabetes. This differs from some international guidelines that include HbA1c (glycated haemoglobin) as a diagnostic criterion.

The American Diabetes Association defines prediabetes as an HbA1c between 5.7% and 6.4%, but SEMDSA does not currently endorse HbA1c alone for prediabetes diagnosis in South Africa. HbA1c is used locally primarily to diagnose established diabetes (at 6.5% or higher) rather than to identify the prediabetic state. This distinction matters when interpreting your test results.

How is prediabetes diagnosed in South Africa?

SEMDSA 2017 guidelines recommend glucose-based testing for prediabetes diagnosis. The diagnostic thresholds are as follows.

Fasting plasma glucose (measured in mmol/L after an 8-hour overnight fast):

• Normal: below 5.6
• Impaired fasting glucose (IFG): 6.0 to 6.9
• Diabetes: 7.0 or higher

2-hour plasma glucose during an oral glucose tolerance test (OGTT, measured in mmol/L, 2 hours after a 75-gram glucose drink):

• Normal: below 7.8
• Impaired glucose tolerance (IGT): 7.8 to 11.0
• Diabetes: 11.1 or higher

HbA1c (measured as a percentage):

• Normal (ADA): below 5.7
• Prediabetes range (ADA only, not SEMDSA-endorsed for diagnosis): 5.7 to 6.4
• Diabetes: 6.5 or higher

Random plasma glucose (measured in mmol/L):

• Normal: below 5.6
• Inconclusive range: 5.6 to 11.0
• Diabetes: 11.1 or higher

SEMDSA 2017 recommends glucose-based measurement, specifically fasting plasma glucose or the OGTT, for diagnosing prediabetes in South Africa. HbA1c is used locally primarily for diagnosing established diabetes.

If your initial test suggests prediabetes, SEMDSA recommends confirming the result with a second test on another day before making a definitive diagnosis. This reduces the risk of misdiagnosis due to temporary factors that can affect glucose levels, such as recent illness, stress, or medication use.

The fasting plasma glucose test requires an overnight fast of at least 8 hours and is the simplest screening method. The OGTT is more sensitive and involves measuring glucose before and 2 hours after drinking a standardised glucose solution (75 grams of glucose). Whilst more time-consuming, the OGTT can detect IGT that might be missed by fasting glucose alone.

What causes prediabetes?

Prediabetes develops when the body becomes less responsive to insulin, a hormone that helps glucose move from the bloodstream into cells for energy. This condition, called insulin resistance, forces the pancreas to produce more insulin to maintain normal blood glucose levels. Over time, the pancreas may struggle to keep up with this increased demand, leading to elevated glucose levels that fall into the prediabetic range.

Several risk factors increase the likelihood of developing prediabetes.

Age and family history: Risk increases after age 45, and having a first-degree relative (parent or sibling) with type 2 diabetes substantially raises risk.

Weight and body composition: Overweight (BMI of 25 or higher, or 23 or higher in individuals of South Asian descent) and central obesity are major risk factors. In South Africa, waist circumference thresholds are 94 cm or more for men and 80 cm or more for women (90 cm or more for South Asian men).

Previous gestational diabetes: Women who developed diabetes during pregnancy face significantly elevated risk. In South Africa, approximately 10% of pregnancies are affected by gestational diabetes, and roughly 50% of these women progress to type 2 diabetes within 5 years.

Polycystic ovary syndrome (PCOS): This hormonal condition is strongly associated with insulin resistance and prediabetes risk.

Cardiovascular risk factors: Hypertension (blood pressure 140/90 mmHg or higher, or on antihypertensive therapy) and dyslipidaemia (HDL cholesterol below 0.9 mmol/L, or triglycerides above 2.82 mmol/L) frequently coexist with prediabetes.

Physical inactivity: Sedentary behaviour contributes to insulin resistance and weight gain.

Ethnicity: In South Africa, Black African, Indian, and Coloured populations have higher prevalence of type 2 diabetes and prediabetes compared with White populations. Studies suggest that as many as 1 in 4 South African adults older than 45 may have type 2 diabetes, with prediabetes prevalence estimated at approximately 15% nationally.

Why prediabetes matters

Prediabetes is not a benign condition. Without intervention, it carries substantial health risks both in the short term and over a lifetime.

Progression to type 2 diabetes: In untreated individuals, annual progression rates from prediabetes to diabetes range from approximately 5% to 10%, with cumulative lifetime risk approaching 70% in some populations. The Da Qing Diabetes Prevention Study found that 96% of individuals with prediabetes who received no intervention developed diabetes over 30 years.

Cardiovascular risk: Prediabetes is associated with increased cardiovascular disease risk independent of whether diabetes develops. A large meta-analysis involving over 10 million individuals found that prediabetes was associated with increased rates of cardiovascular disease, coronary heart disease, stroke, and all-cause mortality compared with normal glucose levels. The absolute risk difference was roughly 8.75 additional cardiovascular events per 10,000 person-years and 7.36 additional deaths per 10,000 person-years.

Microvascular complications: Even before diabetes develops, prediabetes can be associated with early signs of retinopathy (eye damage), peripheral neuropathy (nerve damage), and chronic kidney disease. Studies show that 7% to 16% of individuals with prediabetes already have evidence of these complications.

The good news is that these risks are modifiable. Prediabetes represents an opportunity to intervene before irreversible damage occurs.

Can prediabetes be reversed?

Yes, prediabetes can often be reversed with sustained lifestyle changes. Reversal means returning to normal glucose tolerance, which substantially reduces the risk of developing diabetes and its complications.

The strongest evidence comes from the Diabetes Prevention Program (DPP), a landmark trial conducted in the United States. Participants with prediabetes who followed an intensive lifestyle intervention reduced their risk of developing diabetes by 58% over 3 years compared with those who received standard care. The intervention focused on achieving at least 7% weight loss and 150 minutes of moderate-intensity physical activity per week.

Long-term follow-up studies demonstrate that the benefits persist. The DPP Outcomes Study showed a 34% reduction in diabetes risk at 10 years, 27% at 15 years, and 24% at 21 years. The Da Qing Diabetes Prevention Study in China reported a 39% reduction in diabetes risk at 30 years.

Weight loss is the most important factor. A recent meta-analysis found that the relationship between weight loss and diabetes prevention follows a linear pattern: any amount of weight loss from 1% to 9% provides benefit, with greater weight loss conferring greater protection. Achieving 5% to 10% weight loss is particularly effective.

Importantly, physical activity alone, even without achieving weight loss goals, reduced diabetes incidence by 44% in the DPP.

However, reversal does not eliminate the need for ongoing vigilance. Individuals who return to normal glucose tolerance remain at higher risk than those who never had prediabetes and require continued annual screening and maintenance of healthy lifestyle habits.

What to do if you have prediabetes

If you have been diagnosed with prediabetes, the following evidence-based steps can reduce your risk of progression to diabetes and improve your overall health.

Lifestyle intervention is first-line treatment. This is the most effective approach and carries minimal risk.

Weight loss: If you are overweight or obese, aim for 5% to 10% weight loss. This level of weight reduction has been shown to decrease diabetes risk by approximately 58% over 3 years in clinical trials. A realistic pace is 0.5 to 1 kilogram per week.

Physical activity: Target at least 150 minutes of moderate-intensity aerobic activity per week, such as brisk walking, distributed over at least 3 days. Resistance training 2 to 3 times per week targeting major muscle groups provides additional benefit.

Medical nutrition therapy: No single diet has been proven superior for prediabetes, so dietary counselling should be tailored to individual preferences and cultural context. Evidence supports several eating patterns:

• Mediterranean-style diet: Emphasises fatty fish, nuts, seeds, olive oil, whole grains, legumes, fruits, and vegetables. This pattern has the strongest evidence for reducing cardiovascular disease risk and improving glucose metabolism.
• DASH (Dietary Approaches to Stop Hypertension) diet: Focuses on fruits, vegetables, whole grains, lean proteins, and low-fat dairy whilst limiting sodium, saturated fat, and added sugars.
• Low-carbohydrate approaches: May be appropriate for some individuals, particularly when focused on reducing refined carbohydrates and processed foods.

General principles include minimising consumption of sugar-sweetened beverages, refined grains, red meat, and processed or ultra-processed foods whilst emphasising non-starchy vegetables, whole fruits, legumes, lean proteins, whole grains, nuts, seeds, and fibre (at least 14 grams per 1,000 calories).

Medication: Metformin may be considered for select high-risk individuals, though this is not a registered indication in South African primary care for prediabetes specifically. International guidelines suggest metformin may be considered for individuals with BMI of 35 or higher, age below 60, or a history of gestational diabetes. This is a decision made with your GP, taking the full clinical picture into account.

Annual re-screening: Once diagnosed with prediabetes, SEMDSA recommends annual retesting with fasting plasma glucose or OGTT, not HbA1c, to monitor glucose status.

Cardiovascular risk assessment: Because prediabetes is associated with elevated cardiovascular risk, your GP should assess blood pressure, lipid profile, and smoking status, and address these risk factors as appropriate.

When to see a GP

If screening suggests prediabetes, whether through workplace health checks, pharmacy screening, or self-testing, the next step is a proper consultation with a GP. Your GP can interpret results in the context of your full medical history, confirm the diagnosis with appropriate repeat testing, assess your overall cardiovascular risk, screen for complications, and develop an individualised follow-up plan.

A GP consultation is also essential for discussing realistic weight loss strategies, obtaining referral to a registered dietitian for medical nutrition therapy, addressing coexisting conditions such as hypertension or dyslipidaemia, and determining whether medication might be appropriate in your specific situation.

For comprehensive support in managing prediabetes and reducing your risk of progression to diabetes, our approach to chronic disease care focuses on evidence-based prevention and individualised treatment plans. To discuss your results and develop a personalised strategy, book a consultation.