What is the recommended approach for diabetes screening in a patient, particularly those 45 years or older, or those with risk factors such as obesity, physical inactivity, or a family history of diabetes?

Diabetes Screening Recommendations

Primary Screening Recommendation

Screen all adults beginning at age 45 years using fasting plasma glucose (FPG), repeating every 3 years if results are normal. 1 For adults younger than 45 years who are overweight or obese (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans), screening should be performed if they have one or more additional diabetes risk factors. 1

Who Should Be Screened

Age-Based Screening

• All adults ≥45 years: Universal screening recommended regardless of other risk factors 1
• Adults <45 years: Screen only if overweight/obese AND have additional risk factors 1

Risk Factor-Based Screening (for those <45 years with BMI ≥25 kg/m²)

Screen if the patient has any one of the following: 1

• First-degree relative with diabetes
• High-risk race/ethnicity (African American, Latino, Native American, Asian American, Pacific Islander)
• History of cardiovascular disease
• Hypertension (≥140/90 mmHg or on antihypertensive therapy)
• HDL cholesterol <35 mg/dL and/or triglycerides >250 mg/dL
• Women with polycystic ovary syndrome
• Physical inactivity
• History of gestational diabetes or delivery of baby >9 lbs
• Other conditions associated with insulin resistance (severe obesity, acanthosis nigricans)

Important BMI threshold adjustment: For Asian Americans, use BMI ≥23 kg/m² instead of ≥25 kg/m² due to equivalent diabetes risk at lower BMI values. 1

Recommended Screening Tests

First-Line Test

Fasting plasma glucose (FPG) is the preferred screening test because it is faster, easier to perform, more convenient and acceptable to patients, less expensive, and more reproducible than alternatives. 1

Alternative Acceptable Tests

The following tests are equally appropriate for screening: 1

• A1C (≥6.5% indicates diabetes; 5.7-6.4% indicates prediabetes)
• 2-hour plasma glucose during 75-g oral glucose tolerance test (OGTT) (≥200 mg/dL indicates diabetes; 140-199 mg/dL indicates impaired glucose tolerance)

Diagnostic Thresholds

Diabetes diagnosis: 1, 2

• FPG ≥126 mg/dL (7.0 mmol/L)
• 2-hour OGTT ≥200 mg/dL (11.1 mmol/L)
• A1C ≥6.5%
• Random plasma glucose ≥200 mg/dL with symptoms of hyperglycemia

Prediabetes diagnosis: 1

• FPG 100-125 mg/dL (impaired fasting glucose)
• 2-hour OGTT 140-199 mg/dL (impaired glucose tolerance)
• A1C 5.7-6.4%

Screening Intervals

• Normal results: Repeat screening at minimum 3-year intervals 1
• Prediabetes: Test annually 1
• History of gestational diabetes: Lifelong testing at least every 3 years 1
• High-risk individuals: Consider more frequent testing based on risk profile 1

Confirmation Requirements

In the absence of unequivocal hyperglycemia, abnormal results must be confirmed by repeat testing on a separate day. 1, 3 This confirmation step is critical to rule out laboratory error and establish a definitive diagnosis. 3

• If the same test is repeated and both results exceed the diagnostic threshold, diabetes is confirmed 1
• If two different tests (e.g., A1C and FPG) both exceed diagnostic thresholds, diabetes is confirmed 1
• Exception: A single random plasma glucose ≥200 mg/dL with classic symptoms (polyuria, polydipsia, unexplained weight loss) confirms diabetes without repeat testing 1, 4

Critical Caveats and Pitfalls

A1C Limitations

A1C should NOT be used in certain conditions where red blood cell turnover is altered: 1

• Sickle cell disease
• Pregnancy (second and third trimesters)
• Recent blood loss or transfusion
• Hemodialysis
• Erythropoietin therapy

In these situations, use only plasma glucose criteria for diagnosis. 1

Hemoglobin Variants

Hemoglobin variants can interfere with A1C measurement, though most U.S. assays are unaffected by common variants. 1 Marked discrepancies between A1C and plasma glucose should prompt consideration that the A1C assay may be unreliable for that individual. 1

Fasting Requirements

For FPG testing, fasting is defined as no caloric intake for at least 8 hours. 1, 5 Testing in the non-fasting state invalidates FPG results. 5

Community Screening Not Recommended

Community-based screening outside healthcare settings is not recommended due to lack of evidence for cost-effectiveness and potential for harm without adequate follow-up and interpretation. 1 Screening should be performed within the healthcare setting where proper interpretation, counseling, and follow-up can be ensured. 1

Special Population: Children and Adolescents

Testing should be considered in overweight or obese children and adolescents (BMI >85th percentile) who have additional risk factors for diabetes, though the evidence base for A1C use in this population is limited. 1