RBC vs blood cell

RBC and blood cell both are nouns.

Word	Noun	Adjective	Verb	Adverb
RBC	Yes	No	No	No
blood cell	Yes	No	No	No

As nouns, blood cell is a hypernym of RBC; that is, blood cell is a word with a broader meaning than RBC:

RBC: a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus
blood cell: either of two types of cells (erythrocytes and leukocytes) and sometimes including platelets

Other hypernyms of RBC include blood corpuscle, corpuscle.

RBC (noun)	blood cell (noun)
a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus	either of two types of cells (erythrocytes and leukocytes) and sometimes including platelets