Managing Diabetes Blood Tests: HbA1c, Glucose & What to Expect

Why Blood Tests Matter for Diabetes

Diabetes affects approximately 4.3 million people in the UK, with an estimated further 850,000 living with undiagnosed type 2 diabetes. Regular blood testing is the cornerstone of diabetes management — it is how you and your healthcare team know whether your blood sugar is well controlled, whether your treatment is working, and whether complications are developing.

Poorly controlled blood sugar over time can damage blood vessels, nerves, kidneys, and eyes. The good news is that regular monitoring allows early intervention, and keeping your levels within target ranges significantly reduces the risk of complications. This guide explains each blood test used in diabetes care, what the results mean, and how often you should be tested.

HbA1c (Glycated Haemoglobin)

HbA1c is the single most important blood test for people with diabetes. It measures the percentage of haemoglobin — the oxygen-carrying protein in red blood cells — that has become glycated (coated with sugar). Because red blood cells live for approximately 120 days, HbA1c reflects your average blood glucose level over the past 2 to 3 months, giving a much more useful picture than a single glucose reading.

In the UK, HbA1c is reported in millimoles per mol (mmol/mol). The key thresholds, as set out by NICE, are:

• Below 42 mmol/mol (6.0%) — Normal, no diabetes.
• 42 to 47 mmol/mol (6.0 to 6.4%) — Pre-diabetes (non-diabetic hyperglycaemia). You are at higher risk of developing type 2 diabetes and should be retested annually.
• 48 mmol/mol (6.5%) or above — Diabetes. Diagnosis requires two separate results at or above this level, unless symptoms are present.

For people already diagnosed with type 2 diabetes, NICE recommends an HbA1c target of 48 mmol/mol (6.5%) for those managed with lifestyle changes alone or a single medication not associated with hypoglycaemia. For those on medications that can cause low blood sugar (such as insulin or sulphonylureas), the target is typically 53 mmol/mol (7.0%). Your GP or diabetologist may set an individualised target based on your circumstances.

HbA1c does not require fasting and can be taken at any time of day, making it particularly convenient for home blood testing.

Fasting Blood Glucose

A fasting blood glucose test measures the concentration of glucose in your blood after you have not eaten for at least 8 hours (usually overnight). It is one of the standard tests used to diagnose diabetes and assess how well your body regulates blood sugar at rest.

• Below 5.5 mmol/L — Normal fasting glucose.
• 5.5 to 6.9 mmol/L — Impaired fasting glucose (pre-diabetes).
• 7.0 mmol/L or above — Suggests diabetes (must be confirmed on a second occasion if asymptomatic).

Because this test requires fasting, it is best performed first thing in the morning. If you are having your blood taken at home, an early-morning appointment is ideal.

Random Blood Glucose

A random glucose test can be taken at any time, without fasting. It is less precise for diagnosis but useful when diabetes is suspected based on symptoms such as excessive thirst, frequent urination, and unexplained weight loss. A random glucose of 11.1 mmol/L or above, combined with symptoms, is diagnostic of diabetes.

Oral Glucose Tolerance Test (OGTT)

The OGTT is used primarily to diagnose gestational diabetes during pregnancy (usually at 24 to 28 weeks) and sometimes to investigate borderline results from other tests. After an overnight fast, a blood sample is taken, then you drink a 75g glucose solution. A second blood sample is taken 2 hours later.

• 2-hour glucose below 7.8 mmol/L — Normal glucose tolerance.
• 7.8 to 11.0 mmol/L — Impaired glucose tolerance.
• 11.1 mmol/L or above — Diabetes.

C-Peptide

C-peptide is a protein released into the blood when the pancreas produces insulin. Measuring C-peptide helps distinguish between type 1 and type 2 diabetes and can show how much insulin your pancreas is still making. Low or undetectable C-peptide levels typically indicate type 1 diabetes or advanced type 2 diabetes where the pancreas has become exhausted. This test is usually requested by a specialist rather than as a routine screening tool.

How Often Should You Be Tested?

NICE guidelines recommend the following monitoring schedule:

• Newly diagnosed type 2 diabetes — HbA1c every 3 months until stable, then every 6 months.
• Stable type 2 diabetes — HbA1c every 6 months.
• Type 1 diabetes — HbA1c every 3 to 6 months.
• Pre-diabetes — HbA1c or fasting glucose annually.
• Annual review — Should include kidney function (eGFR, urine ACR), cholesterol, and liver function alongside HbA1c.

If your treatment changes — for example, a new medication is started or the dose is adjusted — your GP may check HbA1c again after 3 months to assess the effect.

Understanding Your Results

Blood test results are only meaningful in context. A single slightly elevated reading does not necessarily mean your diabetes is poorly controlled. Factors such as illness, stress, changes in diet, and even the time of year can temporarily affect your levels. Your GP or diabetes nurse will look at the trend over multiple tests rather than reacting to a single result.

If your HbA1c is consistently above your target, your healthcare team may suggest changes to your diet, exercise routine, or medication. If it is well controlled, that is excellent evidence that your current management plan is working.

Getting Tested at Home

For people with diabetes who need regular blood tests, visiting a GP surgery or hospital phlebotomy department every few months can be time-consuming and inconvenient. A mobile phlebotomist can visit your home at a time that suits you, take the necessary samples, and have them sent to an accredited laboratory. Results are typically available within 24 to 48 hours.

This is especially helpful for people with mobility difficulties, busy work schedules, or those who simply prefer the comfort and convenience of being tested at home. All Lola Dispatch phlebotomists are DBS-checked and qualified to perform venous blood collection for diabetes monitoring tests including HbA1c, glucose, and full metabolic panels.