Average Glucose Concentration Over Time (Glycated Hemoglobin A1c)
This test measures the average level of blood sugar (glucose) over the past 2–3 months, reflecting long-term blood sugar control.
["Helps doctors assess how well diabetes or prediabetes is managed over time."]
Key facts at a glance
- LOINC
- 104638-2
- Short code
- Gluc SD/Gluc mean RptPrd NFr In fld calc
- Synonyms
- Gluc SD/Gluc mean RptPrd NFr In fld calc
- Category
- glucose
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 5 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- calculated
- CPT
- 85610
- SNOMED
- 396252006
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why Is This Test Done?
Your doctor may order this test to monitor blood sugar levels in people with diabetes or prediabetes. It provides a clearer picture than daily blood sugar checks alone, as it accounts for fluctuations throughout the day and week.
How Is the Test Performed?
A small blood sample is taken from your arm, usually during a routine visit. The test measures the percentage of hemoglobin molecules that have been glycated (attached to glucose).
What Does the Result Mean?
Results are often reported as a percentage (e.g., 5.7%–6.4% is considered prediabetes; 6.5% or higher may indicate diabetes). A lower percentage suggests better blood sugar control, while a higher percentage may indicate poor management.
What Are Possible Causes of Abnormal Results?
Elevated HbA1c levels may be due to poorly controlled diabetes, certain medications, or conditions like kidney disease or thyroid disorders. Lower levels could indicate over-treatment or temporary factors like recent illness.
Reference range
INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A
Inform your healthcare provider if you are taking blood thinners. No special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: HbA1c is a critical marker for diabetes management because it reflects average glucose exposure over time, reducing the impact of short-term spikes or drops. Regular monitoring helps prevent long-term complications like nerve damage, kidney disease, or heart disease.
Short name
HbA1c
Frequently asked questions
How often should I get this test if I have diabetes?
What if my HbA1c is higher than expected?
Can diet or exercise affect my HbA1c results?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
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Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy