From: Rabbi Moshe Sofer
To: Rabbi Yehoshua
A woman experienced hargashah and checked with her chemise, finding a clean discharge and blood drops smaller than a gris. The Chasam Sofer rules leniently, reasoning that the sub-gris blood drops can be attributed to lice on the garment while the clean discharge accounts for the substance that exited during the hargashah, though one who is stringent will receive blessing.
Source: Shu"t Chasam Sofer YD §180