Diabetes mellitus in a non-pregnant person is diagnosed neither "by impression" nor by a single glucometer reading in the corridor. ADA 2026, Table 2.1, gives four equally valid entry points. Any one is enough — provided the confirmation rule, covered in the next lesson, is followed.
HbA1c ≥6.5% (≥48 mmol/mol). The test is performed in a laboratory using a method certified by the National Glycohemoglobin Standardization Program (NGSP) and standardised to the Diabetes Control and Complications Trial (DCCT) reference assay. NGSP here is a certification programme for the HbA1c method; DCCT in this phrase is the name of the reference assay, not the type 1 diabetes trial itself (that will appear in Module 3). It is not "the average sugar over three months" in the everyday sense: HbA1c is the fraction of haemoglobin irreversibly glycated over the lifespan of the erythrocyte, with greater weight given to the most recent weeks.
Fasting venous plasma glucose (FPG) ≥126 mg/dL (≥7.0 mmol/L). Fasting means no caloric intake for at least 8 hours.
2-hour plasma glucose during an OGTT with 75 g of anhydrous glucose ≥200 mg/dL (≥11.1 mmol/L). The protocol is as described by the WHO. Before the test, three days of mixed diet with ≥150 g of carbohydrate per day: carbohydrate restriction before the load falsely raises post-load glucose (ADA 2026, §2).
Random plasma glucose ≥200 mg/dL (≥11.1 mmol/L) plus classic symptoms of hyperglycaemia or a hyperglycaemic crisis. Random means at any time of day, regardless of meals. ADA names the classic symptoms directly: polyuria, polydipsia, unexplained weight loss. It counts diabetic ketoacidosis (DKA) and the hyperosmolar hyperglycaemic state (HHS) as crises.
The MoH RK 2022 protocol adds an important distinction between media that is absent from ADA Table 2.1. For venous plasma, the fasting diabetes threshold is the same: ≥7.0 mmol/L. For capillary whole blood the fasting threshold is ≥6.1 mmol/L. The post-load and random threshold of 11.1 mmol/L is the same for both media. The RK protocol accepts HbA1c ≥6.5% as a diagnostic criterion with reference to WHO 2011 and requires an NGSP/DCCT method. It considers HbA1c normal up to 5.7% — here the Kazakh protocol coincides with the lower bound of ADA prediabetes, not with "normal up to 6.5".
Why there are four doors and not one. They catch different pieces of physiology. FPG mainly reflects overnight hepatic glucose production. The 2-hour OGTT point reflects peripheral glucose uptake and the incretin response. HbA1c reflects chronic exposure. ADA states directly: agreement between the results of different tests (concordance) is incomplete; 2-h PG diagnoses more people than FPG and HbA1c. So "my HbA1c is normal, so an OGTT is not needed" is not a rule. For routine screening of non-pregnant individuals, ADA considers FPG or HbA1c more convenient; the OGTT is more sensitive and is preferred in specific situations (cystic fibrosis, post-transplant diabetes).
ADA 2026 considers continuous glucose monitoring (CGM) insufficiently supported for screening and diagnosing prediabetes or diabetes. CGM is a management tool, not a fourth "substitute" in Table 2.1.
A teaching case as a construct. A person without complaints, FPG 7.4 mmol/L. This is already the diabetic threshold for venous plasma. It is not yet a closed diagnosis if there is no obvious symptomatic hyperglycaemia: a second abnormal result is needed. This is exactly where the next lesson leads. Here it is enough to remember: the threshold is not "around seven", but ≥7.0 for fasting plasma, ≥11.1 after a load or with symptoms, and ≥6.5% for HbA1c.