histiocytosis vs blood disease

histiocytosis and blood disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
histiocytosis	Yes	No	No	No
blood disease	Yes	No	No	No

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

histiocytosis: a blood disease characterized by an abnormal multiplication of macrophages
blood disease: a disease or disorder of the blood

Other hypernyms of histiocytosis include blood disorder.

histiocytosis (noun)	blood disease (noun)
a blood disease characterized by an abnormal multiplication of macrophages	a disease or disorder of the blood