Keywords：专著资料, 全文在线浏览, 中西医结合, 临床资料, 第2部分
Section Index
3. Diagnosis and Differential Diagnosis
(1) Diagnosis
Clinical diagnosis of diabetes should be based on venous plasma glucose levels rather than capillary blood glucose measurements. The internationally accepted diagnostic criteria and classification system is the WHO 1999 standard. The diagnostic criteria and classification table for diabetes and glucose metabolism status are shown in Tables 2–3.
Table 2: Diagnostic Criteria for Diabetes
| Diagnostic Criterion | Venous Plasma Glucose (mmol/L) |
|---|---|
| 1. Typical diabetic symptoms | ≥ 11.1 |
| (Polydipsia, polyuria, polyphagia, unexplained weight loss) | |
| Plus random blood glucose or | |
| 2. Fasting blood glucose or | ≥ 7.0 |
| 3. 2-hour post-glucose load blood glucose | ≥ 11.1 |
| For individuals without typical diabetic symptoms, a repeat test on another day is required for confirmation. | |
| Note: Fasting state refers to at least 8 hours without caloric intake; random blood glucose refers to blood glucose measured at any time of the day, regardless of the last meal, and cannot be used to diagnose fasting hyperglycemia or impaired glucose tolerance. |
Table 3: Classification of Glucose Metabolism Status (WHO 1999)
| Glucose Metabolism Classification | Venous Plasma Glucose (mmol/L) |
|---|---|
| Normal glucose level | < 6.1 |
| Impaired fasting glucose (IFG) | ≥ 6.1, < 7.0 |
| Impaired glucose tolerance (IGT) | < 7.0 |
| Diabetes | ≥ 7.0 |
| Note: IFG and IGT are collectively referred to as impaired glucose regulation, also known as prediabetes. Fasting plasma glucose or 2-hour plasma glucose values following a 75-g oral glucose tolerance test (GTT) can be used independently for epidemiological surveys or population screening. However, if the purpose of the GTT is to clarify glucose metabolism status, only fasting and 2-hour post-load blood glucose levels need to be measured. According to Chinese data, focusing solely on fasting blood glucose results in a higher rate of missed diagnoses; therefore, ideal screening involves measuring both fasting blood glucose and 2-hour post-GTT blood glucose. Blood glucose levels at other time points during the GTT are not used as diagnostic criteria. It is recommended that individuals with impaired glucose regulation undergo GTT testing to improve the diagnosis rate of diabetes. |
During acute infections, trauma, or other stressful situations, temporary elevations in blood glucose may occur. If there is no clear history of diabetes, such blood glucose levels alone cannot be used to diagnose diabetes clinically; a follow-up test is required after the stress has subsided to reassess glucose metabolism status. Measuring glycated hemoglobin (HbA1c) can also aid in diagnosis. In 2011, the WHO recommended using HbA1c for diagnosing diabetes in countries and regions where conditions permit, with a diagnostic cutoff of HbA1c ≥ 6.5%. The "Chinese Guidelines for the Prevention and Treatment of Type 2 Diabetes (2020 Edition)" defines 5.7% ≤ HbA1c < 6.5% as prediabetes and sets HbA1c ≥ 6.5% as the diagnostic criterion for diabetes.
(2) Differential Diagnosis
-
Differential Diagnosis of Diabetes
The primary goal is to rule out other causes of positive urine glucose tests and various secondary forms of diabetes, such as familial diabetes, neonatal diabetes, chronic nephritis, nephrotic syndrome, Fanconi syndrome, etc., which may present with renal glycosuria but have normal blood glucose and glucose tolerance. Acute stress states like traumatic brain injury, cerebrovascular accidents, and acute myocardial infarction can also lead to stress-induced glycosuria and transient hyperglycemia, even abnormal results on oral glucose tolerance tests (GTT), but these conditions typically resolve once the stress subsides. Post-gastrojejunostomy, hyperthyroidism, autonomic dysfunction, or severe liver disease can likewise cause postprandial hyperglycemia and glycosuria. There are also non-glucose-related glycosurias—for example, taking large doses of vitamin C can produce false-positive results. -
Differentiation Between Type 1 and Type 2 Diabetes
Blood glucose levels alone cannot distinguish between type 1 and type 2 diabetes. Currently, the diagnosis of type 1 diabetes is mainly based on clinical characteristics. Type 1 diabetes typically presents with the following features: age of onset usually under 30 years; prominent "three polys and one less" symptoms; onset often accompanied by ketosis or ketoacidosis; non-obese body type; markedly reduced fasting or postprandial serum C-peptide concentrations; and the presence of autoantibodies such as glutamic acid decarboxylase antibody (GADA), islet cell antibody (ICA), human islet cell antigen 2 antibody (IA-2A), and zinc transporter 8 antibody (ZnT8A). If the classification is uncertain, a provisional classification can be made initially to guide treatment. Subsequently, the clinical presentation should be reevaluated and the subtype reassessed based on the patient’s response to treatment and follow-up observations. Among type 1 diabetes, there is a slowly progressive subtype known as latent autoimmune diabetes in adults (LADA), which in its early stages resembles the clinical presentation of type 2 diabetes and requires GADA and other islet autoantibody tests for definitive diagnosis.
This chapter is prepared for online research and reading; for external materials, please align with original publications and the review process.