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LOINC Code 74299-9: Tyrosine/Phenylalanine post therapeutic diet (DBS) [Molar ratio]

74299-9 is a LOINC code used to identify Tyrosine/Phenylalanine 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 Tyrosine/Phenylalanine^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 Tyrosine/Phenylalanine^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

Tyrosine/Phenylalanine [Molar ratio] in DBS --post therapeutic diet
Tyrosine/Phenylalanine^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 tyrosine to phenylalanine ratio.
After; Blood; CHEMISTRY.CHALLENGE TESTING; DBS; Dried blood spot; Filter paper; FP; p diet; Phe; 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

Tyrosine/Phenylalanine post therapeutic diet (DBS) [Molar ratio]Tyrosine/Phenylalanine [Molar ratio] in DBS --post therapeutic dietTyrosine/Phe p diet DBS-sRtoTyrosine/Phenylalanine^post therapeutic dietCHALTyrosine/Phenylalanine - after Therapeutic Diet, Dried blood spotSRto

Frequently asked questions

Code details

Code74299-9
SystemLOINC
Display nameTyrosine/Phenylalanine post therapeutic diet (DBS) [Molar ratio]
DescriptionTyrosine/Phenylalanine^post therapeutic diet
Short nameTyrosine/Phe p diet DBS-sRto
ComponentTyrosine/Phenylalanine^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

Tyrosine/Phenylalanine - after Therapeutic Diet, Dried blood spot

Part names

Tyrosine/Phenylalanine^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.