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.

LOINCActiveBoth

LOINC Code 78354-8: Arterial-alveolar oxygen Partial pressure ratio

Name: LOINC Code 78354-8: Arterial-alveolar oxygen Partial pressure ratio
Creator: HealthAssure Clinical Team
Published: 2026-05-21T08:59:58.756Z

78354-8 is a LOINC code used to identify Arterial-alveolar oxygen Partial pressure ratio 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 Oxygen.arterial/Oxygen.alveolar. It is commonly used with the system or sample type BldA+Resp.alv.

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 Oxygen.arterial/Oxygen.alveolar. It is commonly used with the system or sample type BldA+Resp.alv.

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: Both
Method: Calculated

What it does not mean

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

Key facts

Arterial-alveolar oxygen Partial pressure ratio

Oxygen.arterial/Oxygen.alveolar

The arterial/alveolar oxygen tension ratio, also known as a/APO2, is a measure of gas-exchange. While it was originally believed to be less affected by the fraction of inspired oxygen (FiO2) compared to other measures such as the alveolar-arterial oxygen tension difference (PAO2-PaO2), the a/APO2 has been found to be somewhat dependent on FiO2, especially with higher degrees of pulmonary shunting. [PMID3742320]

ABG; ALV; ART; Art bld; Art blood; Arterial; Arterial blood; Blood arterial; Calc; Calculation; Lung; O2; O2 A; Point in time; PULMONARY; Pulmonology; QNT; Quan; Quant; Quantitative; Random; Respiratory; tO2

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

Arterial-alveolar oxygen Partial pressure ratioa/A PO2 RtoOxygen.arterial/Oxygen.alveolarPULMPPresRtoPtBldA+Resp.alv

Frequently asked questions

Code details

Code78354-8

SystemLOINC

Display nameArterial-alveolar oxygen Partial pressure ratio

DescriptionOxygen.arterial/Oxygen.alveolar

Short namea/A PO2 Rto

ComponentOxygen.arterial/Oxygen.alveolar

PropertyPPresRto

TimingPt

System (specimen)BldA+Resp.alv

ScaleQn

MethodCalculated

ClassPULM

Example unitsratio

StatusACTIVE

Order/ObservationBoth

Flags

BillableNo

Valid clinical useNo

Source

SourceLOINC

Version2.82

Releasemain

First released2.54

Last changed2.73

Part names

Oxygen.arterial/Oxygen.alveolarPPresRtoPtBldA+Resp.alvQnCalculatedPartial pressure ratioPoint in time (spot)Blood arterial + Respiratory system alveolus

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.