Understanding Your Diabetes Blood Tests (Glucose/HbA1c)

A Patient Information Guide

Your diabetic and metabolic screening blood tests help your healthcare team monitor how your body processes sugars and carbohydrates.

These markers are essential for diagnosing diabetes, tracking metabolic health, and protecting long-term organ function.

HbA1c (Glycated Haemoglobin)

Normal Range: 20–41 mmol/mol (under 5.7%)

HbA1c measures the amount of glucose that has chemically attached itself to the haemoglobin inside your red blood cells.

Because red blood cells live for about 3 months, this test provides a reliable average of your blood sugar levels over the past 8 to 12 weeks.

With fasting glucose, this is the most critical test for metabolic health.

• 42–47 mmol/mol (5.7%–6.4%) indicates pre-diabetes, meaning your blood sugars are higher than normal but not yet in the diabetic range.

• 48 mmol/mol (6.5%) or higher on two separate occasions confirms a diagnosis of Type 2 diabetes.

• For individuals already diagnosed with diabetes, a general tracking target is often 48–53 mmol/mol, though your team will customise this to your health profile.

Fasting Plasma Glucose

Normal Range: 3.9–5.5 mmol/L (70–99 mg/dL)

This test measures the exact concentration of glucose floating in your bloodstream at a single point in time. It requires you to consume nothing but water for at least 8 hours before the blood draw.

Your body naturally releases insulin overnight to keep your fasting sugars low. A fasting glucose level between 5.6 and 6.9 mmol/L indicates impaired fasting glucose (pre-diabetes), while a level of 7.0 mmol/L or higher points toward diabetes. Because it is a snapshot, it is easily affected by short-term stress or illness.

Random Blood Glucose

Normal Range: Under 7.8 mmol/L (under 140 mg/dL) depending on when you last ate

Unlike a fasting test, a random blood glucose test can be performed at any time of day without preparation. It is often used as a quick screening tool when a patient presents with sudden symptoms of diabetes.

In a healthy individual, blood sugar levels rarely rise above 7.8 mmol/L, even after a large meal. A random reading above 11.1 mmol/L (200 mg/dL), especially when accompanied by symptoms like extreme thirst, frequent urination, or unexplained weight loss, strongly suggests diabetes.

Oral Glucose Tolerance Test (OGTT) 2-Hour Glucose

Normal Range: Under 7.8 mmol/L (under 140 mg/dL) after 2 hours

The OGTT evaluates how efficiently your body clears sugar out of your blood after a heavy carbohydrate load. You will have a fasting blood draw, drink a highly concentrated, sugary glucose beverage, and then rest for 2 hours before a second blood draw.

This test is highly sensitive and frequently used to diagnose gestational diabetes during pregnancy. A 2-hour result between 7.8 and 11.0 mmol/L indicates impaired glucose tolerance, whereas a reading of 11.1 mmol/L or higher confirms diabetes.

C-Peptide

Normal Range: 0.26–1.39 nmol/L (0.8–4.2 ng/mL)

When your pancreas manufactures insulin, it creates it as a large molecule that splits into two equal parts: one molecule of active insulin and one molecule of C-peptide. While insulin is quickly cleared by your liver, C-peptide remains stable in your blood much longer.

Measuring C-peptide tells your doctor exactly how much insulin your pancreas is still capable of producing on its own. A very low or undetectable C-peptide level suggests an autoimmune condition like Type 1 diabetes, where the pancreas cannot make insulin. A high level points toward Type 2 diabetes, where the body makes plenty of insulin but cannot use it properly (insulin resistance).

Fasting Insulin

Normal Range: Less than 174 pmol/L (under 25 uIU/mL)

Fasting insulin tracks the baseline level of insulin circulating in your blood before you eat. Insulin is the vital hormone that acts like a key, unlocking your cells so glucose can move out of the bloodstream and be used for energy.

If your cells become resistant to insulin, your pancreas has to work overtime, pumping out higher and higher amounts of the hormone just to keep your blood sugar normal. High fasting insulin is an early warning sign of metabolic syndrome and insulin resistance, often showing up years before your actual blood glucose levels begin to climb.

Fructosamine

Normal Range: 200–285 umol/L

Fructosamine is a protein marker that measures glucose linked to albumin rather than haemoglobin. Because albumin breaks down much faster than red blood cells, fructosamine reflects your average blood sugar control over just the preceding 2 to 3 weeks.

This test is not part of a standard diabetes check, but it is an essential alternative tool. Doctors rely on it when a standard HbA1c test would be inaccurate, such as in patients with sickle cell anaemia, rapid red blood cell turnover, severe blood loss, or during rapid changes in pregnancy.

Ketones (Blood Beta-Hydroxybutyrate)

Normal Range: Less than 0.6 mmol/L

When your body’s cells are completely starved of glucose due to a lack of insulin, your metabolism shifts gears. It begins rapidly breaking down fats for fuel instead, which produces an acidic byproduct called ketones.

A tiny amount of ketones can be normal during fasting or low-carbohydrate dieting. However, if blood ketones climb above 1.5 to 3.0 mmol/L in a person with diabetes, it indicates a critical, life-threatening medical emergency known as Diabetic Ketoacidosis (DKA), which requires immediate emergency hospital treatment.

Other Important Measurements: Microalbuminuria (Urine ACR)

Typical Target: Less than 3.0 mg/mmol

While urine tracking is not a blood test, your healthcare provider will request a morning urine sample at least once a year alongside your diabetic blood screening.

Why Urine ACR Matters: Consistently elevated blood sugars place an immense amount of physical stress on the delicate filtering units inside your kidneys. A urine Albumin-to-Creatinine Ratio (ACR) test checks for microscopic leaks of protein into your urine. Catching a minor protein leak early allows your team to prescribe protective medications before permanent kidney damage occurs.

How Often Should You Get Diabetic and Metabolic Screening?

Your screening or monitoring schedule is guided by your current metabolic health status and whether you are adjusting medications: