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Re: [RC] [RC] Blood test levels - Eleanor Kellon



On Feb 7, 2008 7:33 PM, <heidi@xxxxxxxxxxxxxxx> wrote:
 
The labs I always used preferred to do whole blood Se, but always told us that it was more accurate, not that there was any consistent difference.
 
Selenium is highly protein bound, including to hemoglobin, so whole blood levels will always be higher. This is the full text of the Se yeast vs selenite equine study:
 
 
Note toward the bottom that the plasma Se pre exercise was in the range of 160 to 168, whole blood 201 to 205 - because of the Se sequestered in red cells. This is true across species.
 
 
Whole blood is also more accurate in terms of true selenium level. For example, with acute toxicities, most is bound to tissues proteins throughout the body, including inside the red cells, while free/ionic selenium is rapidly excreted by the kidneys. Plasma levels in that situation can be misleading low:
 
 
With borderline whole body/tissue deficiency status, the tissues including the red cells will become depleted first. In that scenario, whole blood levels will approach serum levels until frank deficiency sets in - so whole blood levels will test low while serum would test normal.
=================
Too bad about not having the bloodwork--that would have been interesting.  In most horses, it takes 60-90 mg or more per day over a prolonged period (a couple of months) to get signs of toxicity.  (That's slightly less than 10x the daily recommendation of 8-10 mg, to put it in perspective.  And of course, that was average-sized horses--you'd have to "pro-rate" that for a smaller Icelandic, I would think.)  I would wonder about breed differences--perhaps Icelandics are more efficient with their Se and less tolerant of excesses than other breeds??

I wondered about that too. Found a survey of trace elements in Icelandic forages. Coastal and mountainous areas are adequate at 0.1 to 0.2 ppm, otherwise low. Who knows? Could only find one study on Icelandics in Iceland, looking at GSH-Px activity rather than Se levels directly. Levels were all over the place, and baseline dietary intakes unknown. It starts on page 83:
 
 
Had another client with an inactive horse (recovering laminitic), forage selenium tested and virtually undetectable, full size horse this time (Arab cross), put on 3 mg/day Se yeast and serum selenium came back 190 (high for serum) a year later. This is well below anything toxic but surprising. Might have been a post feeding peak, but it's difficult to get serum Se over 160 or so with selenite.
 
Clearly we need a lot more information, but personally I'm careful with the Se yeast. With the selenite, there's a potential for inhibition of absorption (e.g. by copper, arsenic in drinking water in some areas) so when balancing rations and using selenite I always took that into consideration. With the Se yeast, there's both better absorption and no potential for inhibited absorption. Totally agree though that working horses need more than current recommended minimum intakes.
 
Eleanor

Replies
RE: [RC] Blood test levels, heidi