It will depend on your set-up / "accuracy". A few possibilities:
- some current sensors use an external resistor to set gains. You can switch in a higher value resistors to increase the gain in the low current mode.
- you can use a variable gain opamp to increase the gain in the low current mode.
- you can use a higher resolution adc.
- you can lower the AVref in the low current mode.
...
Some of the suggestions above are actually for increased "resolution", not "accuracy", which I think may be what you were asking for actually.
The best way to increase accuracy is actually to use a better adc + reference.