The World Health Organization diagnoses diabetes using three main blood tests, each with a specific cutoff value. A fasting plasma glucose of 7.0 mmol/L (126 mg/dL) or higher, a two-hour plasma glucose of 11.1 mmol/L (200 mg/dL) or higher after an oral glucose tolerance test, or an HbA1c of 6.5% (48 mmol/mol) or higher all qualify for a diabetes diagnosis. These thresholds apply to both type 1 and type 2 diabetes and are largely consistent with the criteria used by the American Diabetes Association.
The Three Diagnostic Tests
Each test measures blood sugar in a different way, and only one abnormal result is needed for diagnosis, though there’s an important catch for people without symptoms.
Fasting plasma glucose (FPG): You fast for at least eight hours, then have blood drawn. A result of 7.0 mmol/L (126 mg/dL) or above indicates diabetes.
Oral glucose tolerance test (OGTT): After fasting, you drink a solution containing 75 grams of glucose. Blood is drawn two hours later. A reading of 11.1 mmol/L (200 mg/dL) or above at the two-hour mark indicates diabetes.
HbA1c: This test reflects your average blood sugar over roughly the past two to three months. No fasting is required. A result of 6.5% (48 mmol/mol) or above indicates diabetes.
There is also a fourth pathway: if you already have classic symptoms of high blood sugar, such as excessive thirst, frequent urination, and unexplained weight loss, a random plasma glucose of 11.1 mmol/L (200 mg/dL) or above at any time of day is enough for diagnosis without any fasting or scheduled test.
Confirming the Diagnosis
If you have no symptoms and a single test comes back above the diabetes threshold, the WHO recommends repeating the test, preferably the same one, on a separate day. This repeat requirement exists because blood sugar can spike temporarily from illness, stress, or other factors. A second abnormal result confirms the diagnosis. When someone already has clear hyperglycemic symptoms, a single test is sufficient.
Prediabetes: Impaired Fasting Glucose and Impaired Glucose Tolerance
The WHO recognizes two intermediate categories between normal blood sugar and diabetes. These are not full diabetes, but they signal elevated risk and are often grouped under the umbrella of “prediabetes.”
Impaired fasting glucose (IFG): A fasting plasma glucose between 6.1 and 6.9 mmol/L (110 to 125 mg/dL). This is slightly different from the ADA’s lower cutoff of 5.6 mmol/L (100 mg/dL), meaning the WHO classifies fewer people as having impaired fasting glucose than the ADA does.
Impaired glucose tolerance (IGT): A two-hour OGTT result between 7.8 and 11.0 mmol/L (140 to 199 mg/dL), with a fasting value below 7.0 mmol/L. This range is the same across both the WHO and the ADA.
For HbA1c, a result between 5.7% and 6.4% is generally considered the prediabetes range. People in either of these intermediate categories have a significantly higher chance of progressing to type 2 diabetes, particularly if both IFG and IGT are present at the same time.
Gestational Diabetes Criteria
The WHO uses a separate set of thresholds for pregnancy because even moderately elevated blood sugar can affect fetal development. The test is the same 75-gram OGTT, but three time points are measured instead of one, and the cutoffs are lower than those for standard diabetes diagnosis.
Gestational diabetes is diagnosed if any single value meets or exceeds these levels:
- Fasting: 5.1 mmol/L (92 mg/dL) but below 7.0 mmol/L
- 1 hour: 10.0 mmol/L (180 mg/dL)
- 2 hours: 8.5 mmol/L (153 mg/dL) but below 11.1 mmol/L
Only one abnormal value is needed. This is a key distinction from the older ADA approach, which previously required two of three abnormal values for a gestational diabetes diagnosis. If the fasting value reaches 7.0 mmol/L or the two-hour value reaches 11.1 mmol/L, the diagnosis shifts from gestational diabetes to diabetes in pregnancy, a category that implies pre-existing type 2 diabetes discovered during pregnancy rather than a condition caused by the pregnancy itself.
WHO vs. ADA: Where the Criteria Differ
For diagnosing diabetes itself, the WHO and the ADA are almost identical. The fasting threshold of 7.0 mmol/L, the two-hour OGTT threshold of 11.1 mmol/L, and the HbA1c cutoff of 6.5% are the same in both systems. The meaningful differences show up in the gray zones.
The biggest gap is in impaired fasting glucose. The WHO sets the lower boundary at 6.1 mmol/L (110 mg/dL), while the ADA starts at 5.6 mmol/L (100 mg/dL). In practice, this means someone with a fasting glucose of 5.8 mmol/L would be classified as having prediabetes under ADA criteria but would be considered normal by WHO standards. This distinction matters if you’re comparing test results against guidelines from different countries, since many nations outside the United States follow WHO criteria.
For gestational diabetes, the WHO applies non-pregnancy glucose thresholds in a simplified, single-step approach: one 75-gram OGTT with lower cutoffs. The ADA has adopted similar thresholds in recent years, though clinical practice still varies by country and hospital.
Types of Diabetes in the WHO Classification
The WHO recognizes four main categories. Type 1 diabetes results from the immune system attacking the insulin-producing cells of the pancreas, which means the body produces little or no insulin. It requires daily insulin from diagnosis onward and typically appears in childhood or adolescence, though it can develop at any age.
Type 2 diabetes is far more common, accounting for roughly 90% of all diabetes cases worldwide. The body still produces insulin but uses it inefficiently, a state often called insulin resistance. It develops gradually, usually in adults, and is strongly linked to excess weight and physical inactivity.
Gestational diabetes develops during pregnancy in people who did not previously have diabetes. It usually resolves after delivery, but it substantially increases the risk of developing type 2 diabetes later in life.
The fourth category covers other specific types, including diabetes caused by genetic conditions, diseases of the pancreas, or certain medications. These are relatively rare but use the same diagnostic glucose thresholds.