What are the plasma glucose and hemoglobin A1c (HbA1c) levels considered prediabetic?

Prediabetes Diagnostic Criteria

Prediabetes is defined by fasting plasma glucose (FPG) of 100-125 mg/dL (5.6-6.9 mmol/L), 2-hour plasma glucose during 75-g oral glucose tolerance test (OGTT) of 140-199 mg/dL (7.8-11.0 mmol/L), or hemoglobin A1c (HbA1c) of 5.7-6.4% (39-47 mmol/mol). 1

Diagnostic Criteria for Prediabetes

The American Diabetes Association (ADA) has established clear criteria for diagnosing prediabetes using three different measurements:

1. Fasting Plasma Glucose (FPG):

   • 100-125 mg/dL (5.6-6.9 mmol/L)
   • Also known as Impaired Fasting Glucose (IFG)

2. 2-hour Plasma Glucose during 75-g OGTT:

   • 140-199 mg/dL (7.8-11.0 mmol/L)
   • Also known as Impaired Glucose Tolerance (IGT)

3. Hemoglobin A1c (HbA1c):

   • 5.7-6.4% (39-47 mmol/mol)

Any one of these criteria can establish a diagnosis of prediabetes 1.

Risk Continuum

It's important to note that the risk for developing diabetes is continuous, extending below the lower limit of the prediabetes range and becoming disproportionately greater at the higher end of the range 1. This means:

• Individuals with A1C between 5.5% and 6.0% have a substantially increased risk of diabetes (5-year incidence from 9% to 25%)
• Those with A1C between 6.0% and 6.4% have a 5-year risk of developing diabetes between 25% and 50% 1

International Differences

It should be noted that while the ADA defines IFG as FPG levels from 100 to 125 mg/dL, the World Health Organization (WHO) and numerous other diabetes organizations define the IFG lower limit at 110 mg/dL (6.1 mmol/L) 1.

Clinical Implications

Prediabetes should not be viewed as a clinical entity in its own right but rather as an increased risk for diabetes and cardiovascular disease 1. Individuals with prediabetes have approximately a 10% annual risk of progressing to diabetes 2.

Screening Recommendations

The ADA recommends:

• Testing for prediabetes in asymptomatic adults who are overweight/obese and have additional risk factors
• Beginning testing at age 45 for all people
• Repeat testing at minimum 3-year intervals if results are normal 1

Common Pitfalls and Caveats

1. Using only one test: Relying solely on FPG may result in underestimation of prediabetes prevalence. Studies show that when HbA1c is included as a diagnostic test, the prevalence of prediabetes increases significantly 3.

2. Ignoring risk progression: The risk of developing diabetes increases significantly as values approach the upper limit of the prediabetic range 1.

3. Overlooking associated conditions: Prediabetes is associated with obesity (especially abdominal obesity), dyslipidemia with high triglycerides and/or low HDL cholesterol, and hypertension 1.

4. Standardization issues: HbA1c testing should be performed using NGSP-certified methods in an accredited laboratory to ensure accuracy 1.

By understanding these diagnostic criteria and their implications, healthcare providers can identify individuals at risk for diabetes and implement appropriate preventive measures.