Can i measure 450nA with a 6000 count DMM or am i better off just doing a voltage measurement across a resistor and employing ohms law?

I have tried to use a DMM but can't get it to respond.

 

that is 0.5uA so not really... proper thing would be to build suitable amplifier. but... you can try using volts range. most DMMs have input impedance of 10MOhm on most ranges. so 0.45uA*10MOhm = 4.5V. so switch DMM to 20V range (0.45uA will display as 4.5V).
if 4.5Vdrop is too much, place 1.1MOhm resistance (1Meg + 100k in series) in parallel with DMM. that will result in voltmeter input resistance drop from 10 to 1 MOhm so voltage would be 10x lower. for 0.45uA you would be seeing 0.45V


something like

 

Yeah i found doing it the conventional way with a DMM i ran out of decimal places.

 

Be aware though, that many autoranging DMMs change their input impedance between 10 and 11 Megohm, as they step through their different ranges. Check the meter’s user manual for range/impedance info and lock it into a manual range.

But if 10% error is close enough for your requirements, then you don’t need to bother.