blood relative vs blood relation

blood relative and blood relation both are nouns.

Word	Noun	Adjective	Verb	Adverb
blood relative	Yes	No	No	No
blood relation	Yes	No	No	No

As nouns, blood relative and blood relation are synonyms defined as:

blood relative and blood relation: one related by blood or origin; especially on sharing an ancestor with another

Other synonyms of blood relative include cognate, sib.

blood relative (noun)	blood relation (noun)
one related by blood or origin; especially on sharing an ancestor with another	one related by blood or origin; especially on sharing an ancestor with another