Target population for screening
Screening for diabetes mellitus in adults begins with identification of eligible individuals. Current recommendations support universal screening from the age of 35 years, regardless of symptoms, and earlier screening in adults aged 18 to 34 years with overweight or obesity associated with metabolic or cardiovascular risk factors, or a family history of type 2 diabetes. Since type 2 diabetes is often asymptomatic in its early stage, structured screening allows timely diagnosis, lifestyle intervention and prevention of microvascular and macrovascular complications.
Symptomatic patients
In the presence of polyuria, polydipsia, unexplained weight loss, lethargy or recurrent infections, overt hyperglycaemia should be considered. A random plasma glucose ≥ 200 mg/dL in the presence of classic symptoms allows the clinical diagnosis of diabetes mellitus without the need for further confirmation.
Asymptomatic patients — diagnostic tests
In asymptomatic patients, screening may be performed using fasting plasma glucose, glycated haemoglobin or a 75 g oral glucose tolerance test. The oral glucose tolerance test has higher sensitivity for detecting impaired glucose tolerance. Values equal to or above 126 mg/dL fasting, 6.5% glycated haemoglobin or 200 mg/dL at two hours during the tolerance test are compatible with a biochemical diagnosis of diabetes. In asymptomatic individuals, these results should be confirmed with a second measurement using the same method or an alternative method. Persistence of the abnormality confirms the diagnosis and justifies structured metabolic and cardiovascular assessment.
Prediabetes
When results do not meet diagnostic criteria for diabetes but fall within intermediate ranges, prediabetes should be considered. This state corresponds to fasting plasma glucose 100–125 mg/dL, two-hour glucose between 140 and 199 mg/dL during the tolerance test, or glycated haemoglobin 5.7–6.4%. Prediabetes is associated with a higher risk of progression to type 2 diabetes and a higher baseline cardiovascular risk. At this stage, intervention on lifestyle and optimization of metabolic risk factors — including weight, physical activity, diet and arterial hypertension — significantly reduce progression. Annual surveillance is recommended.
Normoglycaemia and screening intervals
In the absence of biochemical abnormalities, the individual is classified as normoglycaemic. In these cases, screening should be repeated every 3 years, and may be brought forward to 1–2 year intervals in individuals with obesity, metabolic syndrome or multiple risk factors. Patients with a previous history of gestational diabetes represent a specific group: a 75 g oral glucose tolerance test is recommended between the 6th and 12th postpartum week, followed by subsequent screening every 1 to 3 years.
Initial assessment after diagnosis
After confirmation of the diagnosis of diabetes mellitus, initial stratification is performed to characterize risk and guide follow-up. Assessment includes screening for microvascular complications and identification of macrovascular risk factors. For the retina, an ophthalmological examination should be performed to assess for diabetic retinopathy. At renal level, measurement of albuminuria and glomerular filtration rate is recommended to assess for nephropathy. In the peripheral nervous system, foot examination allows assessment for sensorimotor neuropathy and ulcer risk. In parallel, a comprehensive cardiovascular assessment should be performed — blood pressure, lipid profile, body mass index, smoking status and other modifiable factors — together with updating vaccination status, with particular attention to influenza, pneumococcal disease and hepatitis B in selected patients.
Clinical integration
This structured pathway allows clinicians to identify who should be screened, correctly interpret laboratory results, distinguish normoglycaemia, prediabetes and diabetes mellitus, and organize the initial assessment of newly diagnosed patients, ensuring an integrated approach aligned with current preventive and therapeutic recommendations.
