Sounds rayciss, REEEEEEEEEE!
ยตg/mL = micrograms per milliliter
ng/mL = nanograms per milliliter
These are very, very tiny amounts.
1 microgram = 0.001 milligram = one millionth of a gram
1 nanogram = 0.000001 milligram = 1 x 10 to the -9 power