Vanillylmandelic Acid (VMA) and Homovanillic Acid (HVA), Pediatric, Urine
Method Description Describes how the test is performed and provides a method-specific reference
Homovanillic acid (HVA) is measured in urine by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Octadecyl (C18) solid-phase extraction is performed on a 1-mL aliquot of urine. The solid-phase extraction column is eluted with 1 mL of methanol. The eluate is evaporated at 30 degrees C to 40 degrees C under nitrogen and the residue is reconstituted in 1-mL LC-MS/MS mobile phase. LC-MS/MS is performed by injecting 10 microL of the reconstituted specimen onto an amide-C16 high-pressure liquid chromatography (HPLC) column. The mobile phase (30% acetonitrile in 0.05% aqueous acetic acid) is pumped over the HPLC analytical column at the rate of 1 mL/min, with the flow diverted to the MS/MS electrospray probe tip by 1:5. HVA elutes apart from the bulk of the specimen matrix at a retention time of approximately 1.5 minutes. HVA is quantitated by using a custom-synthesized stable isotope-labeled internal standard (C-4-hydroxy-O-HVA).(Magera MJ, Stoor A, Helgeson JK, et al: Determination of homovanillic acid in urine by stable isotope dilution and electrospray tandem mass spectrometry. Clin Chim Acta 2001;306:35-41)
Vanillylmandelic acid (VMA) is measured by solid-phase extraction (SPE) of a 1-mL aliquot of urine. A known amount of stable isotope-labeled VMA (IS) is added to each urine specimen prior to SPE. VMA and IS are eluted from the SPE column with methanol. The methanol is evaporated and the VMA and IS are redissolved in LC-MS/MS mobile phase. A portion of this prepared extract is injected onto a LC column that separates VMA and IS from the bulk of any remaining specimen matrix. The VMA and IS are measured by MS/MS using the selected reaction monitoring mode. VMA is quantified using the ratio to IS versus urine calibrators.(Magera MJ, Thompson AL, Stoor AL, et al: Determination of vanillylmandelic acid in urine by stableisotope dilution and electrospray tandem mass spectrometry.Clin Chem 2003;49:825-826)
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Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Friday; 8 a.m.