Why screening matters before symptoms appear

Type 2 diabetes and prediabetes are unusual among chronic conditions because they can remain completely silent for years. There is no pain, no fever, no obvious sign that blood sugar is trending in a dangerous direction. By the time symptoms such as increased thirst, frequent urination, or blurred vision appear, the condition may already be well established.

This is precisely why blood sugar screening is a cornerstone of preventive care rather than a response to symptoms. The Centers for Disease Control and Prevention estimates that more than 80% of Americans with prediabetes do not know they have it. Screening changes that equation by finding a problem while there is still time to change its course.

For a broader picture of which tests matter at each stage of life, see the preventive screenings every adult should know about.

Who should be screened and when

The American Diabetes Association advises screening for type 2 diabetes and prediabetes in adults aged 35 and older, regardless of symptoms. If screening is normal, repeat testing every 3 years is generally recommended. More frequent screening may be appropriate if results are borderline or risk factors change.

Screening is recommended earlier than age 35 for adults who have one or more of the following risk factors:

  • Body mass index (BMI) at or above 25, or at or above 23 in Asian Americans
  • First-degree relative with type 2 diabetes
  • History of gestational diabetes or delivering a baby weighing more than 9 pounds
  • High blood pressure or being treated for it
  • Abnormal cholesterol or triglyceride levels
  • Polycystic ovary syndrome (PCOS)
  • History of cardiovascular disease
  • Physical inactivity

Race and ethnicity also affect risk. Black, Hispanic, Asian American, and Native American adults face higher rates of type 2 diabetes and may benefit from earlier or more frequent screening. Your provider can help determine the right schedule for your situation.

Bring your risk factors to your next appointment

Before your next provider visit, write down any relevant history: family members with diabetes, your weight history, blood pressure readings, and any past abnormal lab results. This helps your provider decide whether early or more frequent screening is appropriate for you. You do not need to wait for a specific symptom to start the conversation.

For a decade-by-decade breakdown of when various health screenings are typically advised, see screening recommendations by age.

Understanding your test results

Three tests are in routine use for diabetes screening, and each captures blood sugar in a slightly different way.

The fasting plasma glucose test measures blood sugar after an 8-hour fast. A result below 100 mg/dL is normal. Between 100 and 125 mg/dL indicates prediabetes. At 126 mg/dL or above on two separate occasions, a diabetes diagnosis is made.

The HbA1c test does not require fasting. It reflects average blood sugar over roughly 3 months by measuring the percentage of hemoglobin coated with sugar. Below 5.7% is normal; 5.7% to 6.4% indicates prediabetes; 6.5% or above on two tests indicates diabetes.

The oral glucose tolerance test (OGTT) involves drinking a sugary solution and having blood drawn 2 hours later. A result of 140 to 199 mg/dL indicates prediabetes; 200 mg/dL or above suggests diabetes.

One abnormal result alone is rarely sufficient for a diagnosis. Illness, stress, and certain medications can temporarily raise blood sugar, so confirmation with a repeat test is standard clinical practice.

96 million

American adults with prediabetes

According to the CDC, approximately 96 million U.S. adults have prediabetes, and more than 80% are unaware of it.

58%

Reduction in diabetes progression with lifestyle changes

The NIH-funded Diabetes Prevention Program found lifestyle intervention reduced progression from prediabetes to type 2 diabetes by 58% over 3 years.

1 in 3

Adults in the U.S. has prediabetes

The CDC reports that roughly 1 in 3 American adults has prediabetes, making it one of the most common undetected metabolic conditions.

What to do if your results show prediabetes

A prediabetes result is not a diabetes diagnosis. For many people, it is an opportunity to change direction before the condition progresses.

The Diabetes Prevention Program, a large clinical trial funded by the National Institutes of Health, found that structured lifestyle changes reduced the progression from prediabetes to type 2 diabetes by about 58% over 3 years among participants who achieved the study's activity and modest weight-loss goals. Medication (specifically metformin) reduced progression by 31% in the same trial, particularly among younger and heavier participants.

Practical steps that support better blood sugar regulation include increasing physical activity, reducing intake of refined carbohydrates and added sugars, and achieving modest weight loss if a provider recommends it. The CDC-recognized National Diabetes Prevention Program offers structured, evidence-based group programs available in many communities and online.

Lifestyle choices interact with screening results in ways that are worth understanding. How lifestyle choices intersect with preventive care covers the connections between sleep, nutrition, activity, and the screenings you may need.

Cardiovascular risk often travels alongside elevated blood sugar. Heart health checks you should not skip explains why combining metabolic and cardiovascular screening gives a more complete picture of your health.

This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your personal health circumstances.