28th May 2025

Diagnosis

T2DM is often asymptomatic at the time of diagnosis, however, signs and symptoms may include:

• Polyuria
• Polydipsia
• Blurred vision
• Unexplained weight loss
• Recurrent infections (e.g. UTIs, skin infections, balanitis).
• Fatigue
• Acanthosis nigricans (dark skin discolouration present in the skin folds, for example, the axillae or groin) is caused by insulin resistance.
• Hyperosmolar hyperglycaemic syndrome (rare presentation).

Screening is not routinely offered for T2DM but patients and testing is up to the discretion of clinicians. The diagnostic criteria are identical to type 1 diabetes (T1DM) and there is the same choice of three blood tests that may be used. A single positive result is sufficient to diagnose a symptomatic patient with diabetes, but, if a patient is asymptomatic, they require two separate positive results taken on different occasions. The diagnostic criteria is used:

• Fasting glucose ≥ 7 mmol/L
• Random (non-fasting) glucose ≥ 11.1 mmol/L
• HbA1c ≥ 48mmol/mol

HbA1c is a measure of the proportion of glycated haemoglobin of the bloodstream. An HbA1c < 48mmol/mol cannot be used to exclude a diagnosis of diabetes as it gives an aggregate of the preceding three months. Post-splenectomy or in functional hyposplenism (for example in coeliac disease) red blood cells have an increased lifespan and therefore have longer to become glycated, giving an inappropriately high HbA1c. Causes of decreased red blood cell life-span will give a falsely negative result, examples include:

• Haemoglobinopathies (e.g. thalassaemia, sickle cell disease)
• Severe anaemia of any cause
• HIV-positive patients
• Recent blood transfusion
• Gestational diabetes
• Childhood diabetes

Patients who have a fasting glucose of 6.1-7 mmol/L have a diagnosis of impaired fasting glucose (IFG) and should be offered an oral glucose tolerance test. A result of 7.8-11.1 mmol/L gives a diagnosis of impaired glucose tolerance (IGT). Both of these diagnoses fall under the colloquial umbrella term ‘prediabetes’ and place an individual at a much greater risk of developing T2DM.

At the time of diagnosis, patients should be assessed for signs of heart failure, atherosclerotic cardiovascular disease (using QRISK2) and chronic kidney disease as this will affect the potential management of their condition. They should be referred to their local eye screening service for assessment of diabetic retinopathy via a dilated eye examination. Their feet must be checked for signs of diabetic foot disease and if evidence is found then they should be referred to the local food protection service.