Line crossed by granny? It's in the blood (6)
I believe the answer is:
plasma
'it's in the blood' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for plasma that I've seen before include "Blood component and type of television" , "Yellow liquid in blood" , "hot stuff" , "Component of TV screen" , "Colourless fluid in blood; green variety of quartz" .)