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Corrected QT Interval (Heart Electrophysiology)

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

["The corrected QT interval helps identify heart rhythm disorders that may require medical attention."]

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

Key facts at a glance

LOINC
8636-3
Short code
Q-T interval corrected
Synonyms
Q-T interval corrected
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 the QT Interval?

The QT interval represents the time it takes for an electrical signal to travel through your heart’s ventricles. A longer QT interval may increase the risk of dangerous heart rhythms, such as torsades de pointes, which can be life-threatening.

Why Is It Corrected?

The QT interval can be affected by factors like heart rate. The correction (QTc) adjusts for heart rate to provide a more accurate comparison across different individuals and conditions.

When Might This Test Be Ordered?

Your doctor may order a corrected QT interval test if you have symptoms like fainting, irregular heartbeat, or if you have a history of heart rhythm problems. It’s also used in screening for genetic conditions or before certain medications are prescribed.

What Does a Result Mean?

Results are not provided in absolute numeric ranges, but a prolonged QTc (above expected thresholds) may signal a need for further evaluation by a healthcare provider.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

QTc

Frequently asked questions

Why do I need this test if I don’t have symptoms?
This test may be part of routine screening, especially if you’re taking medications that affect heart rhythm, have a family history of heart issues, or are at higher risk for certain heart conditions.
What does a prolonged QTc mean?
A prolonged QTc may indicate an increased risk of abnormal heart rhythms. Your doctor will interpret results in the context of your overall health and may recommend further testing or monitoring.
Can diet or exercise affect my QTc?
While diet and exercise generally support heart health, they do not directly alter the QTc measurement. However, maintaining overall cardiovascular health can help reduce risks associated with abnormal heart rhythms.
  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