Diagnosis

  • Progression from impaired fasting glucose or impaired glucose tolerance to T2DM occurs at the rate of 2%–22% (average, about 12%) per year depending on the population studied.
  • Lifestyle modification, including a balanced hypocaloric diet to achieve 7% weight loss in overweight patients and regular exercise of ≥150 min/wk, is recommended for persons with prediabetes to prevent progression to T2DM.1
  • Metformin may be considered in patients with prior GDM, those with body mass index (BMI) ≥35, age <60 years, or those with progressive hyperglycemia.
  • Diagnostic criteria for prediabetes and diabetes are listed in Table 23-1.
Table 23-1: Diagnosis of Diabetes

PrediabetesDiabetesaGestational Diabetesb
FPG100–125 mg/dL (5.6–6.9 mmol/L)
(IFG)		≥126 mg/dL (7.0 mmol/L)≥92 mg/dL (5.1 mmol/L)
2-h 75-g oGTT140–199 mg/dL (7.8–11.0 mmol/L)
(IGT)		≥200 mg/dL (11.1 mmol/L)≥153 mg/dL (8.5 mmol/L)
HbA1C5.7%–6.4% (39–46 mmol/mol)≥6.5% (48 mmol/mol)N/A

FPG, fasting plasma glucose; IFG, impaired fasting glucose; IGT, impaired glucose tolerance; HbA1C, hemoglobin A1C; oGTT, oral glucose tolerance test.

aRequires two tests to confirm diagnosis unless random glucose ≥200 mg/dL (11.1 mmol/mol) with polyuria, polydipsia.

bThese are IADPSG guidelines used internationally. A single abnormal value is considered diagnostic of gestational diabetes on these guidelines. 1-h post 75-g glucose load ≥180 mg/dL (10 mmol/L) can be used for diagnosis of GDM on these guidelines as well. In the United States, a two-step method is still most common: nonfasting 1-h post 50-g glucose challenge ≥140 mg/dL (7.8 mmol/L) (some centers use 130 mg/dL [7.2 mmol/L] or 135 mg/dL [7.5 mmol/L]) ­necessitates a 3-h 100-g oGTT and Carpenter and Coustan Criteria are used for diagnosis (exceeding 2+ of the following thresholds: fasting ≥95 mg/dL [5.3 mmol/L], 1-hour ≥180 mg/dL [10 mmol/L], 2-hour ≥155 mg/dL [8.6 mmol/L], 3-hour ≥ 140 mg/dL [7.8 mmol/L]).

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