Blood disease (7)
I believe the answer is:
anaemia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">blood disease</span>' is the definition.<br/ ><span class="explanation-format__explanation">(anaemia is a kind of blood disease)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for anaemia that I've seen before include "Lack of red corpuscles in blood resulting in weakness" , "Result of iron deficiency" , "cause of pallor" , "Cause of weakness and lack of iron" , "Blood disorder -- ie I am Ana (anag)" .)