Well...(legal rant between stars, if you're not 
interested skip...)

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losing a kidney to obsession (I am assuming the 
donor is the one losing the kidney since if an 
obsessed person stole someone else's kidney it 
would be battery) would infer a specific intent 
to divest oneself of the organ on the part of 
the obsessed.  In Moore v. Regents of the 
University of California 499 U.S. 936 (1991) 
cert. denied, the Supreme Court of California 
ruled that you are not allowed to sell your body 
parts (in this case your cells) OR realize any 
profits from someone modifying them for their 
own nefarious purposes (GREATLY paraphrased). It 
is also illegal (statutorily) to sell body parts 
for the purpose of transplantation or therapy 
(they don't say anything about selling them to 
put in jars on desks or the like).  
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You are, however, allowed to GIVE away your 
organs and if someone, say, wanted to GIVE you 
that cel from episode 23 of Trigun in a 
COMPLETELY unrelated burst of 
generosity...well...*I* wouldn't argue with 
that... o_~

That's probably WAY more than anyone wanted to 
know about the property rights a person has 
concerning their own bodies but I always think 
it's funny when the government tells us what we 
can and cannot do with our own bodies :P