LOINCActiveBoth

LOINC Code 81622-3: Hydroxyapatite (24H U) [Energy diff]

81622-3 is a LOINC code used to identify Hydroxyapatite (24H U) [Energy diff] 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 Hydroxyapatite. It is commonly used with the system or sample type Urine.

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 Hydroxyapatite. It is commonly used with the system or sample type Urine.

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

Hydroxyapatite [Energy Difference] in 24 hour Urine
Hydroxyapatite
Supersaturation of urine correlates with stone type. Measurement of supersaturated urine can be used for the diagnosis and management of patients with renal lithiasis, in patients who have a radiopaque stone, or when stone analysis is not possible. The supersaturation can be used to predict the likely composition. Urine supersaturation changes can also be used to monitor the effectiveness of therapy by confirming that the crystallization potential is been decreased. The differential Gibbs free energy is a measure of the thermodynamic pressure for crystals to form. For this term, a software program, EQUIL [PMID3840540] was used to calculate the urinary supersaturation for the common kidney stone components expressed as the Gibbs free energy of transfer from a supersaturated to a saturated solution. The delta G (DG) will equal zero for solutions at saturation, will be greater than zero for super-saturated solutions, and less than zero for under-saturated solutions. Positive values above the reference mean are associated with increased risk for that type of crystal formation.
1 day; 24 hours; 24HR; Chemistry; Hydroxyapatite deposition disease; Hydroxylapatite crystal; Milwaukee shoulder syndrome; QNT; Quan; Quant; Quantitative; Supersaturation; UA; UR; Urn

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

Hydroxyapatite (24H U) [Energy diff]Hydroxyapatite [Energy Difference] in 24 hour UrineHydroxyapatite 24h EngDiff UrHydroxyapatiteCHEMHydroxyapatite, UrineEngDiff

Frequently asked questions

Code details

Code81622-3
SystemLOINC
Display nameHydroxyapatite (24H U) [Energy diff]
DescriptionHydroxyapatite
Short nameHydroxyapatite 24h EngDiff Ur
ComponentHydroxyapatite
PropertyEngDiff
Timing24H
System (specimen)Urine
ScaleQn
ClassCHEM
Example unitskJ/mol
StatusACTIVE
Order/ObservationBoth

Flags

BillableNo
Valid clinical useNo

Source

SourceLOINC
Version2.82
Releasemain
First released2.56
Last changed2.56

Consumer names

Hydroxyapatite, Urine

Part names

HydroxyapatiteEngDiff24HUrineQnEnergy Difference24 hours

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.

LOINC Code 81622-3 | HealthAssure