Yes, PLASMA is a Scrabble word!

Letter values in Scrabble US: P 3, L 1, A 1, S 1, M 3, A 1.

Is it a valid word?

PLASMA is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the colorless watery fluid of the blood and lymph that contains no cells, but in which the blood cells (erythrocytes, leukocytes, and thrombocytes) are suspended
a green slightly translucent variety of chalcedony used as a gemstone
(physical chemistry) a fourth state of matter distinct from solid or liquid or gas and present in stars and fusion reactors; a gas becomes a plasma when it is heated until the atoms lose all their electrons, leaving a highly electrified collection of nuclei and free electrons

Also: blood plasma.