How is type 2 diabetes diagnosed?

Screening for type 2 diabetes in those at risk is essential to prevent potential complications from developing and should be done even if no symptoms have been observed. Simple blood work to measure specific indicators can result in a reliable diagnosis of type 2 diabetes [1,2].

Screening for type 2 diabetes: why is it important?

Type 2 diabetes is very commonly diagnosed by doctors, even if the patient is not experiencing symptoms. Type 2 diabetes is more common in adults, particularly the elderly, so testing is recommended every three years from age 45 [2].

Some people have a higher risk of developing type 2 diabetes. If you are affected by at least two of the following risk factors, you should request an annual screening, regardless of your age:

• overweight or obese;
• taking antipsychotic medication;
• sedentary lifestyle;
• history of gestational diabetes or family history of type 2 diabetes;
• heart disease;
• high cholesterol or triglyceride levels;
• sleep disorders;
• high blood pressure [1,2].

Early diagnosis of type 2 diabetes makes it possible to limit the impact of hyperglycaemia on the body by making the necessary lifestyle adjustments or pharmaceutical therapy, or both [2].

Blood tests to diagnose type 2 diabetes

Type 2 diabetes is diagnosed with a simple blood test. The test is usually done when the person is fasting, preferably via a blood sample from a laboratory[1]. If a positive result is returned for the first test, a second blood sample should be taken within 14 days to confirm or refute the initial diagnosis [1,2].

Fasting blood glucose test

A fasting blood glucose test involves taking a blood sample when the person has not eaten for at least 12 hours. The aim is to check if blood glucose levels are high without having eaten and thus to detect potential type 2 diabetes. If two measurements taken a few days apart are equal to or greater than 7.0 mmol/L, then a positive diagnosis of diabetes is confirmed [2].

Random blood glucose test

As its name suggests, the random blood glucose test is a blood sample taken at any time during the day. It enables the measurement of glucose levels in the blood without considering the time the patient last ate or drank. Glucose levels measured above 11.1 mmol/l indicate diabetes [2].

HbA1c test

HbA1c (glycated haemoglobin) testing is used to measure the patient's blood glucose levels over the previous two to three months. It allows the identification of chronic hyperglycaemia and, in confirmed cases, to ascertain if the diabetes is improving or worsening [2].

The glycated haemoglobin level is considered too high if it is above 5.7%; if it is higher than 6.5%, diabetes is confirmed [1].

Oral glucose tolerance test

The oral glucose tolerance test measures the glucose level in the blood over several hours. It is carried out in the morning, following an 8-12 hour fast. Just before the first sample, 75 grams of glucose is ingested. A second blood sample is taken two hours later, and if it shows a blood glucose level higher than 11.1 mmol/L, then diabetes is suspected [1,2].

C-peptide test

Diagnosis of type 2 diabetes can also include measuring C-peptide levels, which helps determine the level of insulin production and, therefore, how advanced the condition is. C-peptide is often higher following the onset of type 2 diabetes, then decreases as the condition progresses [1,2].