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Corrected QT Interval (Bazett Formula)

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

This test measures the corrected QT interval, a key part of an electrocardiogram (ECG) used to assess heart rhythm and potential risks for abnormal heartbeats.

Quick summary

["A safer way to check heart rhythm stability beyond raw ECG timing."]

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

Key facts at a glance

LOINC
76635-2
Short code
Q-T interval corrected Bazett
Synonyms
Q-T interval corrected Bazett
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
bazett-formula
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

What Is Corrected QT Interval?

The QT interval on an ECG represents the time it takes for your heart’s electrical signals to fully contract its ventricles. A prolonged QT interval can increase the risk of dangerous heart rhythms, such as Torsades de Pointes. The Bazett formula adjusts the raw QT interval for heart rate to account for variations, providing a more accurate measure of risk.

Why Is This Test Done?

Your healthcare provider may order this test if you have symptoms like fainting, seizures, or irregular heartbeats, or if you have conditions like heart disease, electrolyte imbalances, or certain medications that can affect heart rhythm.

How Is It Performed?

This test is performed during an ECG, a quick, painless procedure where electrodes are placed on your chest. The device records your heart’s electrical activity for about 10 seconds. The corrected QT interval is calculated from this recording.

What Does the Result Mean?

Results are compared to standard ranges to identify if the corrected QT interval is prolonged. While reference ranges vary by lab, a prolonged corrected QT interval may signal an increased risk for abnormal heart rhythms and requires further evaluation by a healthcare provider.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

QTc (Bazett)

Frequently asked questions

What causes prolonged corrected QT intervals?
Prolonged corrected QT intervals can be caused by medications (e.g., certain antibiotics, antidepressants, or antiarrhythmics), electrolyte imbalances (e.g., low potassium or magnesium), heart conditions, or genetic factors. Always discuss all medications and health conditions with your provider before testing.
How often should I get this test?
The frequency depends on your health status. If you have a history of heart rhythm issues or take medications that affect the QT interval, your provider may recommend regular monitoring. Follow-up may also be needed if you experience symptoms like dizziness, chest pain, or palpitations.
Can I eat or drink before this test?
No special preparation is needed for this test. You can eat, drink, and move around normally. However, if you have any concerns or conditions that affect heart rhythm, discuss them with your healthcare provider before the test.
  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