Very darkly discolored finger nail from puncture wound between nail & cuticle. Will I lose nail? How to protect finger tip til nail regrows?

Nail bruising. After trauma to nail, it one can get a pooling of blood under the nail (subungual hematoma) which gives the nail a purple/maroon discoloration. If injury is recent and there is pain, please see dermatologist right away. It may be necessary to drain the blood from under nail. Whether nail will be lost depends on how much trauma and how much blood presses on junction between nail plate and bed.