Yes, REAGIN is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, A 1, G 2, I 1, N 1.

Is it a valid word?

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

an immunoglobulin E that is formed as an antibody against allergens (such as pollen); attaches to cell membranes causing the release of histamine and other substances responsible for the local inflammation characteristic of an allergy