Key Takeaways
- Prediabetes affects an estimated 98 million U.S. adults, and most don't know they have it.
- Current guidelines recommend screening adults ages 35–70 who are overweight or have obesity.
- Three main blood tests are used: fasting plasma glucose, HbA1c, and the oral glucose tolerance test.
- Abnormal results should prompt repeat testing and a conversation with a healthcare provider.
- Lifestyle changes made after a prediabetes diagnosis can significantly reduce the risk of progression to type 2 diabetes.
- Certain risk factors — including family history and gestational diabetes — can qualify individuals for earlier screening.
Diabetes Screening
Diabetes screening is a preventive blood test used to detect elevated blood sugar levels before symptoms appear. It identifies people with prediabetes — a reversible condition — or undiagnosed type 2 diabetes at an early, more treatable stage. Because neither prediabetes nor early type 2 diabetes typically causes noticeable symptoms, screening is the primary way these conditions are caught.
Screening tests measure plasma glucose or glycated hemoglobin (HbA1c) and are interpreted against established clinical thresholds set by organizations such as the American Diabetes Association (ADA) and the U.S. Preventive Services Task Force (USPSTF).
Why Diabetes Screening Matters
Type 2 diabetes is one of the most common chronic conditions in the United States, yet it frequently develops without noticeable warning signs. According to the Centers for Disease Control and Prevention (CDC), more than one in five adults with diabetes don't know they have it. Prediabetes — the precursor state — is even more widespread and even less recognized.
This makes screening essential. A blood test ordered during a routine checkup can reveal elevated glucose levels years before complications such as nerve damage, kidney disease, or vision problems develop. Early detection creates a meaningful window for intervention. As our overview of how early detection works explains, catching a condition before symptoms emerge consistently improves long-term outcomes.
98 million
U.S. adults estimated to have prediabetes
According to the CDC's National Diabetes Statistics Report, approximately 98 million American adults — more than 1 in 3 — have prediabetes.
80%
Of people with prediabetes who are unaware
The CDC estimates that about 80% of adults with prediabetes do not know they have the condition, underscoring the importance of routine screening.
35–70
Age range for USPSTF-recommended screening
The U.S. Preventive Services Task Force recommends blood sugar screening for adults in this age range who have overweight or obesity.
Who Should Be Screened and When
The U.S. Preventive Services Task Force (USPSTF) recommends blood glucose or HbA1c screening for adults aged 35 to 70 who have overweight or obesity (defined as a body mass index of 25 or higher). Screening is also appropriate at younger ages for individuals with one or more elevated-risk characteristics, including:
- A first-degree relative (parent or sibling) with type 2 diabetes
- A history of gestational diabetes or delivering a baby weighing more than 9 pounds
- Polycystic ovary syndrome (PCOS)
- Membership in a higher-risk population group (including African American, Hispanic/Latino, American Indian, Alaska Native, Asian American, and Pacific Islander individuals, among others)
- Consistently high blood pressure or abnormal cholesterol levels
- Physical inactivity
If your results are within normal range, the USPSTF recommends rescreening every three years. Your provider may adjust that schedule based on your individual risk. For a broader picture of which tests apply at different life stages, see our preventive screenings by age guide.
Special populations: Pregnant individuals and children are screened using different protocols. If you are pregnant or managing a chronic condition, work directly with your healthcare team for personalized guidance.
The Three Main Screening Tests
Diabetes screening relies on three established blood tests. Each measures blood sugar differently, and providers may use one or a combination depending on clinical context.
1. Fasting Plasma Glucose (FPG)
This test measures blood glucose after at least 8 hours without eating or drinking anything other than water. A result below 100 mg/dL is considered normal. Values between 100–125 mg/dL indicate prediabetes; 126 mg/dL or higher on two separate occasions indicates diabetes.
2. Hemoglobin A1c (HbA1c)
The HbA1c test reflects average blood sugar over the past two to three months by measuring the percentage of glucose attached to hemoglobin. No fasting is required. An HbA1c below 5.7% is normal; 5.7–6.4% indicates prediabetes; 6.5% or higher on two tests indicates diabetes.
3. Oral Glucose Tolerance Test (OGTT)
Used less commonly for routine screening but more frequently during pregnancy, the OGTT involves drinking a standardized glucose solution and measuring blood sugar two hours later. It requires fasting beforehand and is considered a more sensitive test for detecting abnormal glucose metabolism.
An abnormal result on any single test generally warrants a repeat test before a diagnosis is made, unless symptoms of high blood sugar are also present. Some screenings that don't always come up in routine visits are covered in our article on screenings your doctor may not always mention.
What Happens After an Abnormal Result
A result in the prediabetes range is not a diagnosis of diabetes — it is a signal that blood sugar regulation is trending in the wrong direction. For many people, this is reversible. Research published in peer-reviewed literature, including landmark studies such as the Diabetes Prevention Program, has found that structured lifestyle interventions — involving moderate physical activity and dietary changes — can substantially reduce the risk of progressing from prediabetes to type 2 diabetes.
If screening suggests diabetes, your provider will confirm the result with a repeat test and discuss next steps, which may include referral to an endocrinologist, nutrition counseling, and self-management education. Medication decisions, monitoring plans, and any treatment targets are individualized conversations between you and your care team — this article does not substitute for that guidance.
Diabetes screening complements other preventive blood tests, including blood pressure screening, since hypertension and blood sugar disorders frequently occur together and share many of the same risk factors.
This article is for general health information purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health or before making any decisions related to medical care.