LOINCActiveObservation

LOINC Code 18538-9: Q-T interval Lead V1

18538-9 is a LOINC code used to identify Q-T interval Lead V1 in laboratory and clinical observation data. You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges. LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component QT interval. It is commonly used with the system or sample type Lead V1.

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component QT interval. It is commonly used with the system or sample type Lead V1.

When is it used?

  • Used in lab systems, EHRs, and clinical data exchange.
  • May identify a test, observation, survey item, or clinical document request rather than a diagnosis.
  • Status: ACTIVE
  • Order vs observation: Observation
  • Method: EKG

What it does not mean

  • The code identifies the observation or test, not the actual result.

Key facts

  • Q-T interval Lead V1
  • QT interval
  • Added to accommodate measures defined in CEN/TC251/PT007, SCP-ECG (Standard Communications Protocol for Computerized Electrocardiography)
  • Cardio; Cardiology; ECG; EKG.MEASUREMENTS; Electrocardiogram; Electrocardiograph; Heart Disease; L-V1; Point in time; QNT; Q-T interval; Quan; Quant; Quantitative; Random

Where you may see this code

You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges.

Common synonyms

Q-T interval Lead V1Q-T interval L-V1QT intervalEKG.MEASTimePtLead V1

Frequently asked questions

Code details

Code18538-9
SystemLOINC
Display nameQ-T interval Lead V1
DescriptionQT interval
Short nameQ-T interval L-V1
ComponentQT interval
PropertyTime
TimingPt
System (specimen)Lead V1
ScaleQn
MethodEKG
ClassEKG.MEAS
Example unitss
StatusACTIVE
Order/ObservationObservation

Flags

BillableNo
Valid clinical useNo

Source

SourceLOINC
Version2.82
Releasemain
First released1.0l
Last changed2.48

Part names

QT intervalTimePtLead V1QnEKGQ-T intervalTime (e.g. seconds)Point in time (spot)Electrocardiogram (EKG)

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from LOINC. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.

LOINC Code 18538-9 | HealthAssure