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LOINC Code 74300-5: Phenylalanine/Tyrosine post therapeutic diet (DBS) [Molar ratio]

74300-5 is a LOINC code used to identify Phenylalanine/Tyrosine post therapeutic diet (DBS) [Molar 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 Phenylalanine/Tyrosine^post therapeutic diet. It is commonly used with the system or sample type Bld.dot.

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 Phenylalanine/Tyrosine^post therapeutic diet. It is commonly used with the system or sample type Bld.dot.

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

Phenylalanine/Tyrosine [Molar ratio] in DBS --post therapeutic diet
Phenylalanine/Tyrosine^post therapeutic diet
This test measures the phenylalanine to tyrosine ratio in children who have been diagnosed with phenylketonuria and are on a therapeutic diet for their condition. The parent of the patient collects the dried blood spot specimen at home and sends it to the laboratory. This ratio is used together with the phenylalanine and tyrosine levels to monitor the patient's progress. Notedifferent locations use different monitoring analytes. In some states, tyrosine and phenylalanine levels are used in conjunction with the succinylacetone level instead of the phenylalanine to tyrosine ratio.
After; Blood; CHEMISTRY.CHALLENGE TESTING; DBS; Dried blood spot; Filter paper; FP; p diet; Phe; Phe+Tyr; Phenylalanine +Tyrosine; PKU; Point in time; PPA; PST; QNT; Quan; Quant; Quantitative; Random; Scrto; Substance concentration ratio; Substance ratio; Ther; Tyr; WB; Whole blood

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

Phenylalanine/Tyrosine post therapeutic diet (DBS) [Molar ratio]Phenylalanine/Tyrosine [Molar ratio] in DBS --post therapeutic dietPhe/Tyr p diet DBS-sRtoPhenylalanine/Tyrosine^post therapeutic dietCHALPhenylalanine/Tyrosine - after Therapeutic Diet, Dried blood spotSRto

Frequently asked questions

Code details

Code74300-5
SystemLOINC
Display namePhenylalanine/Tyrosine post therapeutic diet (DBS) [Molar ratio]
DescriptionPhenylalanine/Tyrosine^post therapeutic diet
Short namePhe/Tyr p diet DBS-sRto
ComponentPhenylalanine/Tyrosine^post therapeutic diet
PropertySRto
TimingPt
System (specimen)Bld.dot
ScaleQn
ClassCHAL
Example unitsratio
StatusACTIVE
Order/ObservationBoth

Flags

BillableNo
Valid clinical useNo

Source

SourceLOINC
Version2.82
Releasemain
First released2.46
Last changed2.61

Consumer names

Phenylalanine/Tyrosine - after Therapeutic Diet, Dried blood spot

Part names

Phenylalanine/Tyrosine^post therapeutic dietSRtoPtBld.dotQnSubstance RatioPoint in time (spot)DBS

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.