Yes, ERYTHROCYTE is a Scrabble word!

Letter values in Scrabble US: E 1, R 1, Y 4, T 1, H 4, R 1, O 1, C 3, Y 4, T 1, E 1.

Is it a valid word?

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

a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus

Also: red blood cell.

Not playable in Scrabble US: RBC.