Re: Strange Blood Chemistry

[Susan Evans Garlinghouse <suendavid@worldnet.att.net>]

> My horse keeps turning up with very elevated potassium levels (7.0-7.3)
> in his blood.  The first time I had blood taken on him was after a
> strenuous session of hill exercise and the vet suggested that I
> might have muscle damage and tying up, although no other values
> and nothing physical about the horse indicated this.  He recommended
> taking a "resting" blood test to act as a control.  We did that last
> week after the horse had been essentially at rest for two weeks with
> no exercise but turnout.  The *same* elevated potassium level showed up.
> This has my vet stumped.



Ummmm.....maybe one of the DVMs on the list can comment, but my
understanding has always been to ignore the potassium readings of a
blood sample---this is because the potassium content inside of a blood
cell will continue to leach outside of the cell after the blood has been
drawn, therefore the potassium levels that are measured in the blood
sample do not accurately reflect the potassium levels in the serum while
the blood was in the horse.

And if anyone wants to know why this is so, here's the physiology behind
it---cells maintain what's called an electrical membrane potential by
keeping sodium and potassium compartmentalized away from each other. 
Potassium carries a charge and the concentration of potassium is
considerably higher inside a cell than outside of the cell.  There are
specialized channels in the membranes of the cell that pump ions back
and forth between the interior of the cell and the fluid outside the
cell in order to maintain this electrical gradient.  Okay, I know
everyone's eyes are starting to cross, so here's the part you need to
know---potassium passively leaches from the inside to the outside of the
cell, but requires an energy-driven pump to move potassium back INSIDE
the cell where it belongs.  Once blood has been drawn from the body, the
energy is used up, so the little pumps stop. Potassium is still leaching
from the cell into the extracellular fluid, but it's not being pumped
back in...therefore, the measured potassium levels you observe in your
blood sample are going to be considerably higher than the potassium
levels that are ACTUALLY present inside the horse.  Inside the horse,
most of the potassium is compartmentalized away, inside the cell, and
the actual potassium in the fluid outside is considerably lower.


So, unless I am badly misunderstanding something from your post, you can
totally ignore the potassium readings, because they don't mean a thing.

Hope this helps.

Susan Garlinghouse