Hemoglobin A1c
Measures the percentage of hemoglobin coated with glucose to assess average blood sugar over 2-3 months.
Why This Biomarker Matters
HbA1c is the most reliable indicator of long-term diabetes risk and control. Elevated levels signal need for lifestyle changes or medication to prevent complications.
Clinical Standards & Thresholds
Authoritative diagnostic cutoffs and screening guidelines for Hemoglobin A1c.
HbA1c Diagnostic Categories
NIDDK2025
HbA1c (hemoglobin A1c) is a blood test that reflects average blood sugar levels over the past 2-3 months. It is commonly used to classify whether blood sugar levels fall within the normal range, indicate prediabetes, or meet the commonly used diagnostic threshold for diabetes.
Normal
< 5.7%
Prediabetes
5.7 – 6.4%
Diabetes
≥ 6.5%
Blood sugar levels are within the commonly accepted range.
Blood sugar levels are above the commonly accepted normal range but below the diabetes diagnostic threshold. Indicates increased risk for developing type 2 diabetes.
Meets the commonly used diagnostic threshold for diabetes mellitus. Confirmation on a separate day is generally recommended.
Prediabetes Definitions
NIDDK2025
Prediabetes means blood sugar levels are higher than normal but not high enough to be classified as diabetes. It can be identified by any one of three tests: HbA1c of 5.7-6.4%, fasting plasma glucose of 100-125 mg/dL, or a 2-hour OGTT result of 140-199 mg/dL.
HbA1c in the prediabetes range. Any one prediabetes criterion is sufficient for classification.
Fasting plasma glucose in the impaired fasting glucose range. Any one prediabetes criterion is sufficient.
Oral glucose tolerance test result in the impaired glucose tolerance range. Any one prediabetes criterion is sufficient.
Overview
Hemoglobin A1c measures the percentage of hemoglobin (in red blood cells) that has glucose attached to it. Since red blood cells live about 3 months, HbA1c reflects your average blood glucose over the past 2-3 months. Unlike a single fasting glucose test, HbA1c provides a comprehensive picture of long-term glucose control. It's the gold standard for diagnosing and monitoring diabetes, and elevated levels indicate prediabetes or diabetes.
Related Health Conditions
Conditions where Hemoglobin A1c is commonly tested
Related Health Goals
Treatments & Interventions
Therapies monitored using Hemoglobin A1c
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Tolbutamide sodium
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Clinical Trials
Recent Trials
Family Investigation of Nephropathy and Diabetes (F.I.N.D.)
A Study of Cardiovascular Events iN Diabetes Plus
A Pragmatic Trial Comparing Empagliflozin and Dapagliflozin Through Cluster Randomization Embedded in the Electronic Health Record
EASi-PROTKT™ - A Study to Test Vicadrostat (BI 690517) Taken Together With Empagliflozin in People With Type 2 Diabetes, High Blood Pressure, and Cardiovascular Disease
Intervention for High-normal Blood Pressure in Adults With Type 2 Diabetes
Technical Information (LOINC Codes)
Standardized laboratory codes for this biomarker
41995-2Primary17856-64549-271875-959261-817855-862388-496595-4Available Lab Tests
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Doctors who commonly order this test