So, I've measured pA at 100 V and less. Do you consider that high or low? How about pA at 10 kV. A bit wierd, I know. The Zero Voltage Ammeter was a ground potential. How about 1.5 A at 15 kV?
Knowing how to use the instrumentation is important. Some instruments can be floated from ground a certain amount without problems.
I agree with everyone else. The voltage limit on semiconductor devices is more critical than current. What if we throw a "spark gap" or gas discharge tube or a neon lamp in the mix?