Troublesome blood clots for some of them, Bolivians (6)
I believe the answer is:
emboli
'troublesome blood clots' is the definition.
'emboli' can be an answer for 'clots' (embolus is a kind of clot). I'm not certain of the 'troublesome blood' bit.
'some of them bolivians' is the wordplay.
'some of' indicates a hidden word.
'EMBOLI' can be found hidden inside 'them bolivians'.
'for' is the link.
Can you help me to learn more?
(Another definition for emboli that I've seen is " Blood clots or air bubbles which cause arterial blockages".)