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Hemoglobin A1c Index (Blood, 24-Hour Average Glucose Equivalent)

Published: August 9, 2026Updated: August 16, 2026

This test measures the average blood sugar levels over the past 2–3 months by analyzing your red blood cells. It reflects how well your diabetes or prediabetes is controlled over time.

Quick summary

["HbA1c helps track long-term blood sugar trends and guides treatment decisions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
50983-6
Short code
Horowitz index BldC+IhG-Rto
Synonyms
Horowitz index BldC+IhG-Rto
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

How This Test Works

HbA1c measures the percentage of hemoglobin molecules that are coated with sugar (glycated hemoglobin). Over time, high blood sugar attaches to hemoglobin, forming HbA1c. This test uses a specialized immunoassay to detect and quantify this glycated fraction.

What to Expect Before the Test

No special preparation is needed. You may have a fingerstick for a small blood sample, or your blood may be drawn from a vein. If you’re taking insulin or certain diabetes medications, inform your healthcare provider before testing.

What the Results Mean

Results are typically reported as a percentage (e.g., 5.8%–6.4% for prediabetes, ≥6.5% for diabetes). While exact ranges vary by lab, higher percentages generally indicate poorer blood sugar control.

Common Causes of Abnormal Results

Elevated HbA1c may signal uncontrolled diabetes, while lower levels could reflect recent blood sugar drops or certain medical conditions (e.g., anemia). Rarely, lab errors or hemoglobin disorders (like sickle cell) can affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

HbA1c Index

Frequently asked questions

Why is this test important?
HbA1c is a key tool for diagnosing diabetes, monitoring treatment effectiveness, and preventing long-term complications (e.g., nerve damage, kidney disease). It provides a snapshot of your blood sugar management over time, unlike daily glucose checks.
Can I fast before this test?
No fasting is required, but eating or drinking anything (except water) before the test could dilute your blood sample. If you’re unsure, ask your provider.
Does this test differ from a fasting blood sugar test?
Yes. HbA1c measures long-term sugar levels, while fasting blood sugar checks recent (24-hour) glucose levels. Both are useful but serve different purposes in diabetes care.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy