The NI 9203 can measure micro-amps but the accuracy of such a measurement may be undesirable. For example if measuring a 10uA signal with the 9203 you are looking at +/- 19uA of uncertainty (this does not include noise, and uses the bipolar accuracy values). Most C Series modules that are designed for current measurements 9207(+/- 11uA), 9208 (+/- 8.8uA), etc will have around the same accuracy value. Depending on the value of your current measurements and level of accuracy you are looking for this may be an acceptable degree of uncertainty. If the accuracy is not acceptable then the options available to you are either a DMM (USB-4065) or utilize an accurate shunt resistor and take a measurement with an accurate voltage input module (9205 at the .2V or 1V range). Note that with the latter solution you may have issues with picking the correct resistor value, finding one with a small tolerance to get good accuracy, and cover (my assumption) a 20mA to 1uA range. With the DMM you will have to sacrifice the speed of your measurement for accuracy.