What does this LOINC code represent?

This LOINC code identifies a lab observation, measurement, question, or clinical concept in a standardized format.

Is this enough to understand my test result?

No. The code identifies the test or observation, but the interpretation depends on the actual result, reference range, and clinical context.

LOINCActiveObservation

LOINC Code 18511-6: P wave onset [Time] Reference beat

Name: LOINC Code 18511-6: P wave onset [Time] Reference beat
Creator: HealthAssure Clinical Team
Published: 2026-05-21T11:17:27.589Z

18511-6 is a LOINC code used to identify P wave onset [Time] Reference beat 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 P wave onset. It is commonly used with the system or sample type Reference beat.

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 P wave onset. It is commonly used with the system or sample type Reference beat.

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

P wave onset [Time] Reference beat
P wave onset
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; P prime; Point in time; QNT; Quan; Quant; Quantitative; Random; RefB

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

P wave onset [Time] Reference beatP wave Onset Time RefBP wave onsetEKG.MEASTimePtReference beat

Frequently asked questions

Code details

Code18511-6

SystemLOINC

Display nameP wave onset [Time] Reference beat

DescriptionP wave onset

Short nameP wave Onset Time RefB

ComponentP wave onset

PropertyTime

TimingPt

System (specimen)Reference beat

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

P wave onsetTimePtReference beatQnEKGTime (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.