Blood Glucose & Diabetes Tests: HbA1c, Fasting Glucose, and More

Introduction: Australia's Growing Diabetes Challenge

Diabetes has reached epidemic proportions in Australia. Over 1.9 million Australians currently live with diabetes – that's about 1 in 20 people – and a shocking 500,000 more have diabetes but don't know it yet. Perhaps even more concerning, about 2 million Australians have prediabetes, putting them at high risk of developing type 2 diabetes within 5-10 years.

Yet diabetes is often preventable, and when caught early, completely manageable. Blood glucose tests are your early warning system, allowing you to identify problems before serious complications develop.

This comprehensive guide explains all the key blood glucose tests – fasting glucose, HbA1c, oral glucose tolerance test (OGTT), and random glucose – in plain English. You'll learn what these tests measure, how to interpret your results, what prediabetes and diabetes mean for your health, and most importantly, what you can do about it.

Understanding Blood Glucose: The Basics

Glucose (sugar) is your body's primary energy source. When you eat carbohydrates, they're broken down into glucose, which enters your bloodstream. Your pancreas responds by releasing insulin, a hormone that acts like a key, unlocking cells so glucose can enter and be used for energy.

In healthy people, this system maintains blood glucose within a narrow range – typically 4-6 mmol/L when fasting, and rarely above 7.8 mmol/L after meals.

But when this system breaks down, blood glucose rises to dangerous levels, causing both immediate symptoms and long-term damage to blood vessels, nerves, kidneys, eyes, and heart.

Type 1 vs Type 2 Diabetes: What's the Difference?

Type 1 Diabetes

Type 1 diabetes is an autoimmune condition where the immune system destroys insulin-producing beta cells in the pancreas. Without insulin, glucose can't enter cells and accumulates in the blood.

Key features:

• Usually develops in childhood or young adulthood (but can occur at any age)
• Accounts for about 10-15% of all diabetes in Australia
• Not preventable or reversible
• Requires insulin treatment for life
• Often develops rapidly with dramatic symptoms

Type 2 Diabetes

Type 2 diabetes develops when your body becomes resistant to insulin's effects, and your pancreas can't produce enough insulin to overcome this resistance. Think of it as the cell locks becoming rusty – insulin (the key) has trouble opening them.

Key features:

• Accounts for about 85-90% of all diabetes in Australia
• Usually develops in adults over 45, but increasingly seen in younger people
• Often preventable through lifestyle changes
• May be reversible in early stages with significant weight loss
• Develops gradually, often over years
• Strongly linked to obesity, physical inactivity, and family history

Gestational Diabetes

Gestational diabetes occurs during pregnancy when hormones from the placenta make cells more insulin-resistant. It affects about 12-14% of pregnancies in Australia.

While it usually resolves after delivery, women with gestational diabetes have a 50% chance of developing type 2 diabetes later in life.

The Blood Glucose Tests: Understanding Each One

1. Fasting Blood Glucose (FBG)

This test measures your blood glucose after you haven't eaten for at least 8 hours (usually overnight).

Australian Diagnostic Criteria:

• Normal: 3.6-5.5 mmol/L
• Prediabetes (Impaired Fasting Glucose): 6.1-6.9 mmol/L
• Diabetes: 7.0 mmol/L or higher (on two separate occasions)

Preparation:

• Fast for 8-12 hours (water allowed)
• Take test in the morning when cortisol and glucose are naturally higher
• Avoid unusual physical activity or stress before testing
• Tell your doctor about all medications (steroids, diuretics, and others can affect results)

Advantages: Simple, inexpensive, widely available

Limitations: Only shows glucose control at one moment in time; can be affected by recent illness or stress

2. HbA1c (Glycated Hemoglobin)

HbA1c is the gold standard for assessing long-term glucose control. When glucose is high, it sticks to hemoglobin in red blood cells. Since red blood cells live about 120 days, HbA1c reflects your average blood glucose over the past 2-3 months.

Think of HbA1c as a "glucose memory" – it can't be improved by a few good days before your test. It shows your true average control.

Australian Diagnostic Criteria:

• Normal: Less than 5.7% (39 mmol/mol)
• Prediabetes: 5.7-6.4% (39-47 mmol/mol)
• Diabetes: 6.5% (48 mmol/mol) or higher

Treatment targets for people with diabetes:

• General target: 7% (53 mmol/mol) or less
• Stricter target: 6.5% (48 mmol/mol) for those without hypoglycemia risk
• Relaxed target: 7-8% (53-64 mmol/mol) for elderly, those with complications, or high risk of hypoglycemia

Understanding the percentage:

• 5% HbA1c ≈ average glucose 5.4 mmol/L
• 6% HbA1c ≈ average glucose 7.0 mmol/L
• 7% HbA1c ≈ average glucose 8.6 mmol/L
• 8% HbA1c ≈ average glucose 10.2 mmol/L
• 9% HbA1c ≈ average glucose 11.8 mmol/L
• 10% HbA1c ≈ average glucose 13.4 mmol/L

Advantages:

• No fasting required
• Not affected by recent meals or stress
• Reflects long-term control
• Convenient – can be done any time of day

Limitations:

• Can be inaccurate in certain conditions affecting red blood cells (anemia, hemoglobinopathies, recent blood transfusion)
• May be falsely low in iron deficiency, pregnancy, or recent blood loss
• Slightly more expensive than fasting glucose
• Doesn't show glucose variability (you could have dangerous highs and lows that average out to "good" HbA1c)

3. Oral Glucose Tolerance Test (OGTT)

The OGTT measures how well your body processes a glucose load. You drink a very sweet glucose solution (75g glucose), and blood glucose is measured at fasting, then at 1 hour and 2 hours after drinking.

Australian Diagnostic Criteria (2-hour value):

• Normal: Less than 7.8 mmol/L
• Prediabetes (Impaired Glucose Tolerance): 7.8-11.0 mmol/L
• Diabetes: 11.1 mmol/L or higher

When OGTT is used:

• Pregnancy screening (gestational diabetes) at 24-28 weeks
• When fasting glucose and HbA1c give conflicting results
• Suspected prediabetes with normal fasting glucose
• Evaluating people with symptoms but borderline other tests

Advantages: Most sensitive test for detecting early glucose intolerance

Limitations:

• Time-consuming (2-3 hours at pathology collection centre)
• Requires fasting
• Some people feel nauseated from the sweet drink
• Results can vary day to day

4. Random Blood Glucose

This is glucose measured at any time without fasting. It's used for:

• Emergency diagnosis when someone has diabetes symptoms
• Opportunistic screening during other blood work
• Monitoring glucose control (along with home testing)

Diagnostic criteria:

• Diabetes: 11.1 mmol/L or higher (with symptoms)

Random glucose alone (without symptoms) is not used to diagnose diabetes, but a very high reading warrants follow-up testing.

Prediabetes: Your Wake-Up Call

Prediabetes means your blood glucose is higher than normal but not yet in the diabetes range. In Australia, approximately 2 million people have prediabetes, and most don't know it.

Why prediabetes matters:

• Without intervention, 25-50% of people with prediabetes develop type 2 diabetes within 5-10 years
• Cardiovascular disease risk is already elevated
• Nerve damage may already be starting
• BUT: Type 2 diabetes is often preventable with lifestyle changes at this stage

The good news: Studies show that people with prediabetes who lose 5-7% of body weight and exercise 150 minutes per week can reduce their risk of developing diabetes by 58%. In people over 60, the risk reduction is even higher – 71%.

Reversing prediabetes:

1. Weight loss: Even modest weight loss (5-10% of body weight) dramatically improves insulin sensitivity
2. Regular exercise: 150-300 minutes of moderate activity weekly (brisk walking, swimming, cycling)
3. Dietary changes: Reduce refined carbohydrates, increase fiber, choose whole foods
4. Sleep: Aim for 7-9 hours nightly (poor sleep worsens insulin resistance)
5. Stress management: Chronic stress raises cortisol, which raises blood glucose

Understanding Diabetes Complications

When blood glucose remains elevated over years, it damages blood vessels and nerves throughout your body:

Cardiovascular Disease

People with diabetes have 2-4 times higher risk of heart attack and stroke. Cardiovascular disease is the leading cause of death in people with diabetes.

Diabetic Retinopathy (Eye Damage)

Diabetes is the leading cause of blindness in working-age Australians. High glucose damages tiny blood vessels in the retina. Regular eye exams can catch this early when treatment is most effective.

Diabetic Nephropathy (Kidney Damage)

Diabetes is the most common cause of kidney failure in Australia. About 30-40% of people with diabetes develop kidney disease. Early detection through urine albumin testing allows intervention before irreversible damage occurs.

Diabetic Neuropathy (Nerve Damage)

About 50% of people with diabetes develop nerve damage, causing:

• Tingling, numbness, or pain in feet and hands
• Loss of sensation (increasing risk of unnoticed injuries)
• Erectile dysfunction
• Digestive problems
• Problems with heart rate regulation

Diabetic Foot Problems

Combination of nerve damage and poor circulation makes feet vulnerable to infections and ulcers. Diabetes is the leading cause of non-traumatic lower limb amputations in Australia.

Infections

High glucose impairs immune function, making infections more common and slower to heal.

The crucial point: All these complications are largely preventable with good glucose control. Every 1% reduction in HbA1c reduces microvascular complication risk by 37% and heart attack risk by 14%.

Managing Diabetes: Treatment Approaches

Lifestyle Modifications (Foundation for Everyone)

Diet for Blood Glucose Control

Focus on:

• Low glycemic index (GI) carbohydrates: Whole grains, legumes, most fruits and vegetables (these cause slower, smaller glucose rises)
• High fiber: 25-30g daily (slows glucose absorption)
• Lean proteins: Chicken, fish, legumes, tofu
• Healthy fats: Olive oil, nuts, avocados, fatty fish
• Non-starchy vegetables: Fill half your plate

Limit or avoid:

• Refined carbohydrates: White bread, white rice, pastries, biscuits
• Sugary drinks: Soft drinks, fruit juice, energy drinks, flavored milk
• Processed foods: High in refined carbs and unhealthy fats
• Saturated and trans fats: Fatty meats, full-fat dairy, fried foods

Popular eating patterns that work for diabetes:

• Mediterranean diet: Emphasizes vegetables, olive oil, fish, whole grains
• Low-carbohydrate diets: Can dramatically lower glucose and reduce medication needs (work with your doctor)
• DASH diet: Originally for blood pressure, also improves glucose control
• Plant-based diets: High in fiber, low in saturated fat

Exercise: Your Natural Insulin

Exercise is incredibly powerful for diabetes management:

• Improves insulin sensitivity for up to 72 hours after exercise
• Lowers blood glucose immediately (muscles use glucose without needing insulin)
• Helps with weight loss
• Reduces cardiovascular disease risk
• Improves mood and energy

Recommendations:

• Aerobic exercise: 150-300 minutes weekly of moderate intensity (brisk walking, swimming, cycling)
• Resistance training: 2-3 sessions weekly (weights, resistance bands, bodyweight exercises)
• Reduce sitting time: Break up prolonged sitting every 30 minutes

Safety note: If you take insulin or medications that can cause hypoglycemia, check glucose before and after exercise, and carry fast-acting carbs.

Weight Loss: The Most Powerful Intervention

For people with type 2 diabetes and excess weight, weight loss is transformative:

• 5-10% weight loss: Significantly improves glucose control
• 15% weight loss: Can put diabetes into remission in many people
• Bariatric surgery: For severe obesity, can reverse diabetes in 60-80% of cases

Medications for Type 2 Diabetes

When lifestyle changes aren't enough, medications are added. Australia has excellent PBS-subsidized diabetes medications:

Metformin (First-Line Medication)

How it works: Reduces glucose production by liver, improves insulin sensitivity

Benefits: Effective, inexpensive, doesn't cause hypoglycemia, may help with weight loss

Side effects: Gastrointestinal upset (usually improves over time), rare risk of vitamin B12 deficiency

SGLT2 Inhibitors

Examples: Empagliflozin (Jardiance), Dapagliflozin (Forxiga)

How they work: Cause kidneys to excrete excess glucose in urine

Benefits: Lower glucose, promote weight loss, reduce blood pressure, protect heart and kidneys

Side effects: Increased urination, genital yeast infections, rare diabetic ketoacidosis

GLP-1 Receptor Agonists

Examples: Semaglutide (Ozempic), Dulaglutide (Trulicity)

How they work: Mimic natural hormone that stimulates insulin, slows digestion, reduces appetite

Benefits: Excellent glucose lowering, significant weight loss (5-15%), cardiovascular protection

Side effects: Nausea (usually improves), injection site reactions, expensive

DPP-4 Inhibitors

Examples: Sitagliptin (Januvia), Linagliptin (Trajenta)

How they work: Increase insulin, decrease glucagon after meals

Benefits: Well-tolerated, don't cause hypoglycemia

Sulfonylureas

Examples: Gliclazide, Glimepiride

How they work: Stimulate pancreas to produce more insulin

Benefits: Effective, inexpensive

Side effects: Risk of hypoglycemia, weight gain

Insulin

Essential for type 1 diabetes, and eventually needed by many people with type 2 diabetes as pancreas function declines.

Types: Rapid-acting, short-acting, intermediate-acting, long-acting, and premixed insulins

Blood Glucose Monitoring

Self-Monitoring of Blood Glucose (SMBG)

Using a glucose meter and test strips, you prick your finger and measure glucose levels at specific times:

• Fasting (before breakfast)
• Before meals
• 2 hours after meals
• Before bed
• Before and after exercise
• When feeling hypoglycemic

Target ranges for most adults with diabetes:

• Fasting/before meals: 5.0-7.0 mmol/L
• 2 hours after meals: 5.0-10.0 mmol/L
• Before bed: 6.0-8.0 mmol/L

Continuous Glucose Monitoring (CGM)

CGM systems (like FreeStyle Libre, Dexcom, Medtronic Guardian) provide glucose readings every 1-5 minutes using a sensor placed on your skin. This revolutionary technology shows:

• Glucose trends (rising, falling, stable)
• Overnight glucose patterns
• Response to specific foods and activities
• Alerts for high or low glucose

CGM is PBS-subsidized for type 1 diabetes and insulin-treated type 2 diabetes in Australia.

Risk Factors for Type 2 Diabetes

You're at higher risk if you have:

• Excess weight: Especially abdominal fat (waist >94cm for men, >80cm for women)
• Physical inactivity: Sedentary lifestyle
• Family history: Parent or sibling with diabetes
• Age: Risk increases over 45 (but younger onset is increasingly common)
• Ethnicity: Aboriginal and Torres Strait Islander peoples, Pacific Islander, Indian subcontinent, Middle Eastern ancestry (up to 4 times higher risk)
• Gestational diabetes history: 50% develop type 2 diabetes later
• Polycystic ovary syndrome (PCOS): Insulin resistance is common
• Previous prediabetes diagnosis
• Cardiovascular disease history
• High blood pressure or abnormal cholesterol
• Certain medications: Long-term corticosteroid use

When to Test for Diabetes

Screen if you have symptoms:

• Excessive thirst and urination (especially at night)
• Unexplained weight loss
• Increased hunger
• Blurred vision
• Slow-healing wounds or infections
• Tingling or numbness in hands or feet
• Fatigue

Regular screening (even without symptoms):

• All adults: From age 40-45, every 3 years
• High risk groups: From age 18, every 1-3 years (Aboriginal and Torres Strait Islander peoples, those with risk factors)
• Women with previous gestational diabetes: Test 6-12 weeks postpartum, then every 1-2 years

Resources for Further Reading

Conclusion

Blood glucose tests are powerful tools that can detect problems early when they're most treatable. Prediabetes gives you a window of opportunity to prevent type 2 diabetes through lifestyle changes. And if you're diagnosed with diabetes, modern treatments – medications, technology, and knowledge – allow most people with diabetes to live long, healthy lives with minimal complications.

The key is knowing your numbers, understanding what they mean, and taking action. Don't wait until symptoms appear – they often indicate diabetes has already been present for years, potentially causing silent damage.

Whether you're monitoring prediabetes, managing type 2 diabetes, or living with type 1 diabetes, tracking your glucose tests over time is invaluable. BloodResults allows you to store all your HbA1c results, fasting glucose tests, and other blood work in one secure place, visualize trends over months and years, and see whether your lifestyle changes or treatments are working.

Take control of your glucose health today. Know your numbers, understand your risk, and empower yourself with knowledge.