Diagnosis of Type 2 Diabetes: How to Recognize the Disease Early

Type 2 diabetes mellitus (T2DM) is one of the most common chronic diseases worldwide. According to the International Diabetes Federation, 6.7 million people died from diabetes-related causes in 2021. One of the main reasons for such high mortality is late diagnosis. A key feature of T2DM is that it can remain asymptomatic for many years, and by the time it is diagnosed, many patients already have vascular and other complications.

In this article, we will подробно examine how type 2 diabetes is diagnosed—from identifying risk groups to confirming the diagnosis and distinguishing it from other types of diabetes.

Why is early diagnosis so important?

Type 2 diabetes develops gradually. It is often preceded by prediabetes, an intermediate stage where blood glucose levels are higher than normal but not yet in the diabetic range. At this stage, the development of diabetes can be prevented or significantly delayed through lifestyle changes and, if necessary, medication.

Moreover, studies show that without screening, the diagnosis of T2DM may be delayed by 7–9 years from the onset of the disease. During this time, elevated blood glucose silently damages blood vessels, the heart, kidneys, eyes, and nerves.

Thus, timely diagnosis is not just a formality—it is a real opportunity to preserve health for many years.

Who should be screened for diabetes? Risk groups

Not everyone needs to check their blood sugar equally often. Modern clinical guidelines identify groups that should undergo regular screening.

Main risk factors for T2DM:

• Age ≥ 45 years
• Overweight and obesity (BMI ≥ 25 kg/m² for Europeans, ≥ 23 kg/m² for Asians)
• Family history (parents or siblings with T2DM)
• Low physical activity
• Arterial hypertension (≥ 140/90 mmHg or treatment for hypertension)
• Lipid disorders (HDL ≤ 0.9 mmol/L and/or triglycerides ≥ 2.82 mmol/L)
• Polycystic ovary syndrome (in women)
• History of gestational diabetes or delivery of a large baby (> 4.5 kg)
• Cardiovascular diseases (coronary heart disease, stroke, etc.)

Who and when should be screened? (ADA 2025):

1. Adults with overweight/obesity and at least one risk factor — regardless of age
2. All individuals ≥ 35 years — every 3 years
3. People with prediabetes — annually
4. Women with prior gestational diabetes — at least every 3 years (preferably more often)
5. Children and adolescents with obesity and risk factors — from age 10 or onset of puberty

What tests are used for diagnosis?

Four main laboratory tests are used to diagnose T2DM and prediabetes. None is perfect, and sometimes a combination is needed.

1. Fasting plasma glucose (FPG)

Measured after 8–14 hours of fasting.

• < 5.6 mmol/L — Normal
• 5.6–6.9 mmol/L — Impaired fasting glucose (prediabetes)
• ≥ 7.0 mmol/L — Diabetes (requires confirmation)

2. Oral glucose tolerance test (OGTT)

Considered the “gold standard,” especially for early detection.

Procedure:

• Normal diet for 3 days prior (≥150 g carbohydrates/day)
• Overnight fasting (8–14 hours)
• Fasting blood sample
• Intake of 75 g glucose solution
• Repeat blood test after 2 hours

Results (2-hour glucose):

• < 7.8 mmol/L — Normal
• 7.8–11.0 mmol/L — Impaired glucose tolerance (prediabetes)
• ≥ 11.1 mmol/L — Diabetes

New data: Measuring glucose at 1 hour (≥ 11.6 mmol/L) may also indicate T2DM. This approach is promising but not yet routine.

3. Glycated hemoglobin (HbA1c)

Reflects average glucose over 2–3 months. No fasting required.

• < 5.7% — Normal
• 5.7–6.4% — Prediabetes
• ≥ 6.5% — Diabetes

Limitations:

• Affected by anemia, hemoglobinopathies, pregnancy, kidney disease
• May be falsely high or low in some individuals
• If inconsistent with clinical findings, rely on direct glucose measurements

4. Random glucose measurement

Used when symptoms of hyperglycemia are present (thirst, frequent urination, weight loss).

• ≥ 11.1 mmol/L + symptoms — Diabetes

Confirming the diagnosis: why one test is not enough

Diabetes is never diagnosed based on a single elevated result in an asymptomatic patient.

Confirmation rules:

• With classic symptoms: one diabetic-range result is sufficient
• Without symptoms: two abnormal results on different days are required

It is also important to exclude transient hyperglycemia (due to illness, stress, or medications like glucocorticoids).

Prediabetes: a stage not to miss

Prediabetes is not a disease but a serious warning sign.

Diagnostic criteria:

• FPG: 5.6–6.9 mmol/L
• OGTT (2-hour): 7.8–11.0 mmol/L
• HbA1c: 5.7–6.4%

People with prediabetes are at high risk of developing T2DM, but also have the best chance to prevent it through lifestyle changes and possibly medications (e.g., metformin).

Differential diagnosis: Type 1 or Type 2?

Distinguishing T2DM from type 1 diabetes (T1DM) is essential because treatment differs significantly.

Key differences:

• Age of onset: T2DM (usually >40), T1DM (often younger)
• Body weight: T2DM (overweight), T1DM (normal/low)
• Onset: T2DM (gradual), T1DM (acute)
• Ketoacidosis: rare in T2DM, common in T1DM
• Autoantibodies: absent in T2DM, present in T1DM
• C-peptide: normal/high in T2DM, low in T1DM

C-peptide and antibody testing help in unclear cases.

What happens after diagnosis?

After confirming T2DM, patients undergo further evaluation:

• Lipid profile — cardiovascular risk
• Blood pressure — hypertension control
• Kidney function — creatinine, GFR, albuminuria
• Eye exam — diabetic retinopathy
• Foot exam — neuropathy and circulation
• ECG — silent coronary disease

Pre-analytical quality: an overlooked issue

Proper preparation for testing is crucial.

Key points:

• Use tubes with glycolysis inhibitors (sodium fluoride)
• Separate plasma within 30 minutes
• Observe fasting rules

Errors at this stage can lead to false results and missed diagnoses.

Conclusion

Diagnosing type 2 diabetes is a multi-step but well-established process. Modern medicine has reliable tools to detect the disease early—even at the prediabetes stage.

Key takeaways:

1. Do not wait for symptoms—T2DM is often silent.
2. Prediabetes is an opportunity, not a sentence.
3. Diagnosis requires confirmation.
4. Correct classification of diabetes type is essential.
5. Test quality matters.

If you are at risk or over 35, do not delay—start with a simple fasting glucose test. This small step can protect your health for years.

Disclaimer: This article is for informational purposes only. If you suspect diabetes or glucose metabolism disorders, consult an endocrinologist for proper evaluation and treatment.