Can Laboratory Testing Evaluate Diabetes Risk?

Yes. Laboratory testing can help identify prediabetes, diagnose diabetes, and detect changes in blood sugar regulation that may indicate an increased risk of developing type 2 diabetes.

Diabetes often develops gradually. A person can feel completely well while blood sugar levels are already beginning to rise. For this reason, laboratory testing can be an important part of preventive healthcare, particularly for people with risk factors for type 2 diabetes.

Common tests used to evaluate blood sugar include hemoglobin A1C, fasting plasma glucose, and the oral glucose tolerance test. These tests evaluate different aspects of glucose regulation and can help determine whether blood sugar levels are normal, within the prediabetes range, or within the diabetes range.

If you are interested in understanding blood work more broadly, visit our Routine Laboratory Testing Resource Center.

What Laboratory Tests Are Used to Evaluate Diabetes Risk?

The most commonly used laboratory tests for prediabetes and type 2 diabetes are:

• Hemoglobin A1C

• Fasting plasma glucose

• Oral glucose tolerance testing

• Random plasma glucose in certain circumstances

Each test provides somewhat different information.

A physician may use one test initially or compare several measurements when the clinical situation warrants it.

What Is an A1C Test?

Hemoglobin A1C, often simply called A1C, estimates your average blood glucose level over approximately the previous two to three months.

Unlike fasting glucose, an A1C test generally does not require fasting.

For nonpregnant adults, commonly used diagnostic ranges are:

• Normal: below 5.7%

• Prediabetes: 5.7% to 6.4%

• Diabetes: 6.5% or higher

An A1C in the prediabetes range does not mean that type 2 diabetes is inevitable. It does indicate that blood glucose regulation is no longer within the normal range and that the risk of eventually developing type 2 diabetes is increased. Within the prediabetes range, higher A1C values are generally associated with greater diabetes risk.

A1C is particularly useful because it reflects glucose exposure over time rather than what your blood sugar happens to be at one moment.

What Is a Fasting Glucose Test?

A fasting plasma glucose test measures your blood sugar after you have typically gone at least eight hours without consuming calories.

For nonpregnant adults, the commonly used ranges are:

• Normal: 99 mg/dL or lower

• Prediabetes: 100–125 mg/dL

• Diabetes: 126 mg/dL or higher

These thresholds are used by organizations including the American Diabetes Association and the National Institute of Diabetes and Digestive and Kidney Diseases.

Unlike A1C, fasting glucose represents your blood glucose at a particular point in time. Results can therefore be influenced by temporary factors such as illness, stress, recent physical activity, medications, and other physiological changes.

For more information about preparing for laboratory testing, you can also read Understanding Blood Work: A Patient Guide.

What Is an Oral Glucose Tolerance Test?

An oral glucose tolerance test (OGTT) evaluates how your body responds to a specific amount of glucose.

After fasting, your blood glucose is measured. You then drink a standardized glucose solution, and another blood sample is generally collected two hours later.

For a standard 2-hour 75-gram OGTT in nonpregnant adults:

• Normal: below 140 mg/dL

• Prediabetes: 140–199 mg/dL

• Diabetes: 200 mg/dL or higher

The OGTT can identify impaired glucose tolerance that may not always be apparent from fasting glucose alone. However, it takes longer and is less convenient than A1C or fasting glucose, so it is not necessarily required for every patient.

Can Laboratory Testing Find Prediabetes Before You Have Symptoms?

Yes.

One of the most important reasons to screen for diabetes risk is that prediabetes and early type 2 diabetes may exist without obvious symptoms.

Someone may feel healthy while laboratory testing shows that blood sugar regulation has begun to change. Detecting these abnormalities earlier creates an opportunity to address modifiable risk factors before diabetes progresses or complications develop.

This is one reason laboratory testing can be valuable as part of a broader preventive-health strategy.

Learn more about proactive screening in our Preventive Care & Health Optimization Resource Center.

Who Should Consider Diabetes Screening?

Screening recommendations depend on age and individual risk factors.

The American Diabetes Association's 2026 Standards of Care recommend that screening begin at age 35 for adults who do not already qualify for earlier testing based on risk. Risk-based testing may be appropriate sooner for people with overweight or obesity and additional diabetes risk factors.

The U.S. Preventive Services Task Force recommends screening asymptomatic adults ages 35 to 70 who have overweight or obesity for prediabetes and type 2 diabetes.

Factors that may influence the decision to test earlier or more frequently can include:

• Family history of type 2 diabetes

• Overweight or obesity

• History of gestational diabetes

• Polycystic ovary syndrome

• High blood pressure

• Abnormal cholesterol or triglyceride levels

• Cardiovascular disease

• Physical inactivity

• Previous borderline glucose or A1C results

• Certain medications that can raise blood glucose

• Other metabolic risk factors

Your physician can determine which recommendations are most applicable to your individual situation.

Does One Abnormal Blood Sugar Test Mean You Have Diabetes?

Not necessarily.

When someone does not have clear symptoms of diabetes or unequivocal hyperglycemia, an abnormal diagnostic result is generally confirmed with another measurement before a diagnosis is established.

The repeat measurement may involve the same test or a different accepted diabetes test.

For example, an elevated A1C might be repeated or compared with fasting glucose.

This is important because laboratory results should not be interpreted in isolation.

If you receive an unexpected result, reviewing it with your physician is usually more useful than trying to interpret a single number by itself.

You can also read How Often Should You Have Routine Blood Tests? for more information about ongoing laboratory monitoring.

Can A1C Ever Be Misleading?

Yes.

Although A1C is extremely useful, certain conditions can affect its accuracy.

Examples can include:

• Some forms of anemia

• Recent significant blood loss

• Blood transfusions

• Certain hemoglobin variants

• Altered red blood cell lifespan

• Kidney disease

• Some circumstances involving pregnancy

If A1C does not seem consistent with fasting glucose, symptoms, or other clinical findings, your physician may rely more heavily on another glucose-based test or perform additional evaluation.

This is another reason laboratory interpretation requires clinical context rather than simply comparing a number with the reference range.

What About Fasting Insulin?

Fasting insulin is sometimes discussed when evaluating insulin resistance and metabolic health.

However, fasting insulin is not one of the standard diagnostic tests used to diagnose prediabetes or type 2 diabetes.

The established tests for screening and diagnosis remain A1C, fasting plasma glucose, and the oral glucose tolerance test.

In selected situations, a physician may consider insulin measurements or other metabolic markers as supplemental information. Their usefulness depends on the clinical question being asked, and they should not replace established diagnostic testing.

Can Other Laboratory Results Provide Clues About Metabolic Risk?

Yes, although they do not diagnose diabetes by themselves.

A physician evaluating metabolic health may also review laboratory findings such as:

• Triglycerides

• HDL cholesterol

• LDL cholesterol

• Liver enzymes

• Kidney function

• Other cardiovascular risk markers when appropriate

Blood pressure, body composition, waist circumference, family history, nutrition, physical activity, sleep, medications, and previous laboratory trends may also contribute to the overall assessment.

Diabetes risk is therefore best evaluated as part of a broader health assessment rather than from a single laboratory number.

How Often Should Diabetes Testing Be Repeated?

The appropriate interval depends on your results and risk factors.

Current ADA guidance generally recommends repeating screening at least every three years when initial testing is normal, although more frequent testing may be appropriate based on a person's risk profile. People with prediabetes are typically monitored more frequently.

Someone whose A1C has gradually increased over several years may also warrant closer monitoring even if the latest result has not crossed into the diabetes range.

Looking at laboratory trends over time is often more informative than evaluating each result independently.

Can Diabetes Risk Be Reduced If Testing Shows Prediabetes?

Often, yes.

Prediabetes represents an opportunity to identify increased risk before type 2 diabetes is established.

Depending on the individual, a prevention strategy may involve:

• Improving nutrition

• Increasing physical activity

• Losing excess weight when appropriate

• Improving sleep

• Addressing blood pressure and cholesterol

• Stopping tobacco use

• Reviewing medications that may affect blood sugar

• Periodically monitoring A1C or glucose

• Using medication in selected higher-risk individuals

Lifestyle interventions have been shown to reduce progression from prediabetes to type 2 diabetes, which is why identifying prediabetes can be clinically meaningful rather than simply labeling an abnormal laboratory result.

The Bottom Line

Laboratory testing can help evaluate diabetes risk by identifying abnormal blood glucose regulation before symptoms necessarily develop.

A1C, fasting plasma glucose, and oral glucose tolerance testing are established methods for detecting prediabetes and diabetes.

The most useful interpretation considers more than whether a laboratory result is technically normal or abnormal. Your age, previous results, family history, weight, medications, lifestyle, cardiovascular risk factors, and overall medical history can all influence what a result means for you.

If your testing shows an elevated A1C or glucose level, that does not necessarily mean diabetes has already developed. It may instead identify an opportunity for additional evaluation, closer monitoring, and preventive intervention.

For more physician-written information about blood testing, visit the Routine Laboratory Testing Resource Center.

Medical Accuracy & Editorial Standards

This article is intended for general patient education and does not replace individualized medical evaluation, diagnosis, or treatment.

The diagnostic thresholds and screening information discussed in this article are informed by established medical guidance and patient-education resources, including:

• American Diabetes Association – Standards of Care in Diabetes

• American Diabetes Association – Diabetes Diagnosis and Testing

• National Institute of Diabetes and Digestive and Kidney Diseases – Diabetes Tests & Diagnosis

• Centers for Disease Control and Prevention – Diabetes Testing

• U.S. Preventive Services Task Force – Prediabetes and Type 2 Diabetes Screening

Laboratory values should be interpreted within the context of the individual patient. Testing recommendations may differ during pregnancy, in children and adolescents, and in people with conditions that affect the accuracy of specific laboratory measurements.

Author: YiQiu Hu, NMD
Medical Review: YiQiu Hu, NMD
Last Reviewed: August 2026
Clinical Focus: Preventive healthcare, laboratory evaluation, metabolic health, health optimization, and individualized medical care

About the Author

YiQiu Hu, NMD

Dr. YiQiu Hu is an Arizona-licensed naturopathic physician, founder of Ask Dr. Hu, and medical director. His clinical work focuses on concierge medicine, preventive healthcare, health optimization, laboratory evaluation, chronic disease management, medical weight management, hormone care, and individualized treatment planning.

His approach emphasizes thoughtful medical evaluation, appropriate laboratory testing, clear interpretation of results, preventive healthcare, and practical treatment strategies tailored to the individual patient.

Dr. Hu earned his Doctor of Naturopathic Medicine degree from Sonoran University of Health Sciences and a Bachelor of Science in Biomedical Sciences from Northern Arizona University.

Learn more about Dr. YiQiu Hu and the physicians at Ask Dr. Hu.