Lisa,
The SSRI and SNRI might affect the 5-HIAA level causing it to increase.
For HVA, this is linked to dopamine so any medication that cause an increase in dopamine could cause the HVA to be high. If the dopamine beta-hydroxylase enzyme is functioning properly (and not being inhibited by clostridia toxins) than the VMA could be high too VMA is linked to Norepinephrine which gets produced by the conversion of Dopamine from dopamine-beta-hydroxylase.
Dr. Woeller