When should diabetes screening be initiated in adults, what risk factors warrant earlier screening, and which diagnostic tests are appropriate?

Diabetes Screening in Adults

Begin diabetes screening at age 35 years for all adults, or immediately at any age for those with overweight/obesity (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans) plus one or more risk factors. 1

When to Start Screening

Universal Screening Age

• Age 35 years is the current threshold for initiating screening in all adults regardless of risk factors 1
• This represents a shift from the older recommendation of age 45 years, reflecting recognition that earlier detection improves outcomes 1

Risk-Based Earlier Screening

Screen immediately at any age if the patient has overweight/obesity AND one or more of the following risk factors: 1

Family & Genetic Risk:

• First-degree relative with diabetes 1
• High-risk race/ethnicity: African American, Latino, Native American, Asian American, Pacific Islander 1

Metabolic & Cardiovascular Risk:

• Hypertension (≥140/90 mmHg or on antihypertensive therapy) 1
• HDL cholesterol <35 mg/dL or triglycerides >250 mg/dL 1
• History of cardiovascular disease 1
• Physical inactivity 1

Reproductive & Hormonal:

• Women with polycystic ovary syndrome 1
• Women with prior gestational diabetes or who delivered a baby >9 lb 1

Insulin Resistance Markers:

• Severe obesity 1
• Acanthosis nigricans 1

Prior Abnormal Testing:

• Previous A1C ≥5.7%, impaired fasting glucose, or impaired glucose tolerance 1

Medication-Induced Risk:

• Glucocorticoids, statins, thiazide diuretics, certain HIV medications, second-generation antipsychotics 1

Critical BMI Thresholds by Ethnicity

• General population: BMI ≥25 kg/m² 1
• Asian Americans: BMI ≥23 kg/m² (lower threshold reflects increased diabetes risk at lower BMI in this population) 1

Appropriate Diagnostic Tests

First-Line Screening Options

Any of the following three tests are equally appropriate for screening: 1, 2

Fasting Plasma Glucose (FPG):

• Most practical, reproducible, and cost-effective 3, 4
• Requires 8-hour fast 1
• Diabetes: ≥126 mg/dL 1, 3
• Prediabetes: 100-125 mg/dL 1, 2

Hemoglobin A1C:

• Most convenient (no fasting required) 1, 3
• Greater preanalytical stability than glucose tests 2
• Must use NGSP-certified laboratory method 2
• Diabetes: ≥6.5% 1, 3
• Prediabetes: 5.7-6.4% 1, 2

2-Hour 75g Oral Glucose Tolerance Test (OGTT):

• Requires adequate carbohydrate intake (≥150g/day) for 3 days prior to testing 1, 2
• Diabetes: ≥200 mg/dL at 2 hours 1
• Prediabetes: 140-199 mg/dL at 2 hours 1, 2

Test Selection Nuances

• FPG is preferred for routine screening due to practicality and lower cost 3, 4
• A1C should NOT be used in conditions with increased red blood cell turnover (anemia, hemoglobinopathies, pregnancy, hemodialysis, recent blood loss/transfusion, erythropoietin therapy)—use plasma glucose criteria only 2
• OGTT identifies different at-risk populations than FPG or A1C due to incomplete concordance between tests 2

Confirmation Requirements

• Repeat testing on a separate day is required to confirm diagnosis unless the patient has unequivocal hyperglycemia with classic symptoms 1, 3, 4
• If two different tests are both above diagnostic thresholds, diagnosis is confirmed without repeating 1
• Day-to-day glucose variability is 12-15%, so borderline results warrant confirmation 2

Screening Frequency

Standard Intervals

• Every 3 years minimum if initial screening is normal 1, 3
• Annually for patients with prediabetes (A1C 5.7-6.4%, IFG, or IGT) 1
• Every 3 years minimum for women with prior gestational diabetes (lifelong surveillance) 1

Accelerated Screening

Consider more frequent testing (annually or sooner) for: 1

• Patients with borderline results near diagnostic thresholds 2
• Weight gain or worsening risk factor profile 1
• Development of new symptoms 1

Special Medication Monitoring

• Second-generation antipsychotics: Screen at baseline, repeat at 12-16 weeks after initiation, then annually 1
• HIV patients on antiretroviral therapy: Screen before starting therapy, when switching therapy, 3-6 months after starting/switching, then annually if normal 1

Common Pitfalls to Avoid

Don't wait until age 35 for high-risk patients—screen immediately if overweight/obese with any risk factor 1

Don't rely on random glucose alone—sensitivity is only 39-55% for screening 3

Don't use A1C in patients with hemoglobinopathies or conditions affecting red blood cell turnover—plasma glucose criteria only 2

Don't skip confirmation testing—repeat abnormal results on a separate day unless patient is symptomatic 1, 3, 4

Don't conduct community screening outside healthcare settings—ensures proper follow-up and appropriate targeting 1

Don't assume 100 mg/dL fasting glucose is a hard biological threshold—risk is continuous across the entire range, and the 1 mg/dL difference between 99 and 100 mg/dL is clinically arbitrary 2

Don't forget cardiovascular risk factor assessment—when prediabetes or diabetes is identified, evaluate and treat hypertension, dyslipidemia, and other modifiable cardiovascular risks 1