Can I drink black coffee before a diabetes blood test?

No. NHS advice for a fasting blood test is to have nothing except water. Save your coffee or tea, even black, until after your sample.

What is the blood test for diabetes?

The main tests are HbA1c, which shows your average blood sugar over 2 to 3 months, and fasting glucose. This test includes both, plus insulin and C-peptide to show how much insulin your body is making.

What do HbA1c and fasting glucose results mean?

UK guidance treats an HbA1c of 42 to 47 mmol/mol, or a fasting glucose of 5.5 to 6.9 mmol/L, as a high risk of type 2 diabetes. An HbA1c of 48 mmol/mol or more, or a fasting glucose of 7.0 mmol/L or more, suggests diabetes and is confirmed with a second test if you have no symptoms.

Diabetes Status Blood Test at Jace Medical

Heart & metabolic

Private blood test

Diabetes Status Blood Test

HbA1c, glucose, insulin and C-peptide, used to assess blood sugar control and diabetes risk.

4 biomarkers
Fasting required

£49Includes sample collection

Book this test Ask a question

We confirm your appointment and any preparation, such as fasting, before you attend.

What’s included

4 biomarkers in this test.

Fasting required before this test

Blood sugar & diabetes4

How your body manages sugar, including your average level over recent months.

C-peptide
Glucose
Insulin
HbA1c

About this test

Is the Diabetes Status Blood Test right for you?

Who it’s for

You are at higher risk of type 2 diabetes, for example because of your age, ethnic background, weight or a parent, brother or sister with diabetes.
You have been told you have prediabetes or a borderline result. UK guidance suggests a blood test at least once a year if you are at high risk.
You have a condition linked to insulin resistance, such as polyendocrine metabolic ovarian syndrome (PMOS, previously called PCOS).
You want a fuller picture of your blood sugar than HbA1c alone, including how much insulin your body is making.

What it can show

HbA1c shows your average blood sugar over the past 2 to 3 months. It is the main blood test used to check for type 2 diabetes and prediabetes.
Fasting glucose is your blood sugar level at the time of the test, after an overnight fast. It is also used to check for diabetes and prediabetes.
Insulin and C-peptide show how much insulin your pancreas is making. C-peptide is released in equal amounts to insulin and stays in the blood longer, and a raised level can suggest insulin resistance.
C-peptide can also help doctors understand which type of diabetes someone has, alongside other tests.

What it can’t tell you

One raised result is not a diagnosis. If you have no symptoms, diabetes is confirmed with a second blood test.
HbA1c can be misleading if you have anaemia, low iron, a haemoglobin variant such as sickle cell or thalassaemia, a recent blood transfusion, or are pregnant. Steroid medicines and recent illness can also raise blood sugar.
Insulin is not routinely used in UK practice to assess insulin resistance. Your results are best read together with your weight, waist size, blood pressure and cholesterol.
If you have symptoms such as feeling very thirsty, peeing a lot, or losing weight without trying, see your GP promptly rather than waiting for a private test. HbA1c is not suitable when symptoms have come on recently or type 1 diabetes is possible.
Results need to be interpreted alongside your symptoms. Diagnosis and treatment of diabetes are with your GP or specialist.

How it works

From booking to results in three steps.

Step 1
Request your test
Send a booking request online or call us. We confirm your clinic, appointment time and any preparation.
Step 2
Visit the clinic
A short appointment for professional sample collection at Greysteel or Letterkenny. No GP referral needed.
Step 3
Receive your results
Usually within a couple of working days, emailed to you once a doctor has reviewed them.

Common questions