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 21559-0: Theophylline (Gast fld) [Mass/Vol]

Name: LOINC Code 21559-0: Theophylline (Gast fld) [Mass/Vol]
Creator: HealthAssure Clinical Team
Published: 2026-05-25T17:13:11.347Z

21559-0 is a LOINC code used to identify Theophylline (Gast fld) [Mass/Vol] 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 Theophylline. It is commonly used with the system or sample type Gast fld.

Reviewed by HealthAssure Clinical TeamUpdated 25 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 Theophylline. It is commonly used with the system or sample type Gast fld.

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

What it does not mean

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

Key facts

Theophylline [Mass/volume] in Gastric fluid
Theophylline
Aminophylline; Biophyllin; Continus; DRUG/TOXICOLOGY; Drugs; GAST; Gastric contents; Gastric fluid; Lasma; Level; Mass concentration; Nuelin; Phyllocontin; Point in time; Pro-vent; QNT; Quan; Quant; Quantitative; Random; Sabidal SR; Slo-Phyllin; Somophyllin; Somophylline; Theo; Theo-dur; Theolair; Uniphyllin

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.

Related SNOMED CT concepts

705114005SNOMED CT mapping for Theophylline (Gast fld) [Mass/Vol] (21559-0)

Related observations and tests

SNOMED_CT 705114005high

LOINC Code System

Source: LOINC-SNOMED cooperation package

Common synonyms

Theophylline (Gast fld) [Mass/Vol]Theophylline [Mass/volume] in Gastric fluidTheophylline Gast-mCncTheophyllineDRUG/TOXTheophylline, Stomach fluidMCnc

Frequently asked questions

Code details

Code21559-0

SystemLOINC

Display nameTheophylline (Gast fld) [Mass/Vol]

DescriptionTheophylline

Short nameTheophylline Gast-mCnc

ComponentTheophylline

PropertyMCnc

TimingPt

System (specimen)Gast fld

ScaleQn

ClassDRUG/TOX

Example unitsug/mL

StatusACTIVE

Order/ObservationBoth

Flags

BillableNo

Valid clinical useNo

Source

SourceLOINC

Version2.82

Releasemain

First released1.0m

Last changed2.70

Consumer names

Theophylline, Stomach fluid

Part names

TheophyllineMCncPtGast fldQnMass ConcentrationPoint in time (spot)Gastric fluid

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.