Health check is family matter (5,5)
I believe the answer is:
blood count
'health check' is the definition.
(a blood count is a medical check)
'family matter' is the wordplay.
'family' becomes 'blood' (I've seen this in another clue).
'matter' becomes 'count' (both can mean to be of significance).
'blood'+'count'='BLOOD COUNT'
'is' acts as a link.
(Other definitions for blood count that I've seen before include "Dracula?" , "Cell number" .)