Re: can excess potassium befound in the blood on autopsy that suggests homicide

Measurement of potassium in serum can be done by various methods, but ion- 
selective electrode (ISE)is the most common method used in the United 
States. Explanation of how these actually work would take longer than you 
want, but I have included a reference below. Suffice it to say that most 
autoanalyzers used in hospital laboratories use ISEs to measure sodium and 
potassium.

The majority of potassium in the body is within cells.  When the body dies, 
the cells leak potassium into the blood.  About 25 years ago people tried 
to use this as a measure of how long a body had been dead (the higher the 
potassium, the longer since death).  However, the measurements from blood 
are far too erratic to use as a marker for time of death.  People then 
began measuring potassium in the vitreous humor of the eye, which is much 
more stable.  This can be used, along with many other factors such as 
temperature, rigor mortis, age, and others, to ESTIMATE the post mortem 
interval.  (I use the word "estimate" because unlike on TV, you can't 
determine time of death down to the hour.  It's really more like to within 
12-24 hours)

As you know, high concentrations of potassium chloride (KCl) will stop the 
heart, and in fact are used in executions.  Although, autopsies are 
performed on executed bodies in most states for legal reasons, I was not 
able to find any data where anyone tested the blood for exactly how high 
potassium was after lethal injection.  Undoubtedly, the potassium 
concentration would be quite high. Chloride would also be very high if KCl 
was used.  

A pathologist might be suspicious if both potassium & chloride 
concentrations are quite elevated. In addition, it is my understanding that 
it takes quite a bit of very concentrated KCl to cause death. It is very 
difficult to inject someone intravenously without leaving a needle mark (at 
least for the size needle you'd need to inject an adequate volume), so that 
would cause suspicion too.  



Reference
Tietz Textbook of Clinical Chemistry Edited by Carl Burtis and Ed Ashwood. 
3rd Edition.