81622-3

LOINC code 81622-3 identifies "Hydroxyapatite [Energy Difference] in 24 hour Urine". 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 [PMID: 3840540] 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.

This code measures Hydroxyapatite in Urine. It belongs to the CHEM class in the LOINC classification.

LOINC (Logical Observation Identifiers Names and Codes) is a universal standard for identifying laboratory and clinical observations. It is maintained by the Regenstrief Institute and used worldwide for health data exchange.