HVA assay : interference from dietary flavonols

Background: Urinary homovanillic acid (HVA) measurement is used routinely as a marker of first test for the screening of catecholamine-secreting tumours and dopamine metabolism, but generates a large number of false-positive results. With no guidelines for dietary restrictions prior to the test, we hypothesize that consumption of flavonol-rich foods (such as onions, tomatoes, tea) prior to urinary catecholamine screening could be responsible for false-positive urinary HVA in healthy subjects. Methods: A randomized, crossover dietary intervention was carried out in healthy subjects (n=17). Volunteers followed either a low or high-flavonol diet, for a duration of three days, prior to providing a 24hour urine sample for HVA measurement using a routine, validated liquid chromatography method as well as a gas chromatography-mass spectrometry method. Results: Dietary flavonol intake significantly increased urinary HVA excretion (p<0.001), with 3 out of 17 volunteers (20%) exceeding the 40 μmoles/24 h upper limit of normal for HVA excretion (false-positive result). Conclusion: Dietary flavonols commonly found in foodstuff such as tomatoes, onions, and tea, interfered with the routine urinary HVA screening test and should be avoided in the three-day run-up to the test.