Strange Blood Chemistry

["Linda B. Merims" <lbm@ici.net>]

The importance of bloodwork was one of the topics emphasized at
last week's AERC convention, particularly in the talk given by
research veterinarian Jeannie Waldron.  However, Waldron concentrated
only on the two enzymes that seem to be markers for tying up (SGOT and
CPK) and on Chloride levels for electrolytes.  I've got a strange,
unrelated, blood anomaly that I'd like to get some discussion on.

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.   

This is an 18 year old Morgan gelding.  To all appearances he is
healthy, happy, and vigorous.  He is fed approximately 15 pounds
of Canadian mixed timothy hay per day, plus two 14 oz coffee cans
of Purina Equine Senior.  The only supplement is 1,000 IUs per day of
Vitamin E which comes in the form of Horse Health Products'
Vita E Powder, which is mixed in to "Grain Products, Calcium
Carbonate, Vitamin E Supplement, Propionic and Acetic Acids
(Preservatives)."  He has a free choice mineral salt block in his
stall that he consumes only slowly, and has not received any electrolyte
supplementation during the period of these tests.

Here is the complete "resting" blood report:

Glucose..............100
Urea Nitrogen.........11
Creatinine...........1.7
Total Protein........6.9
Albumin..............3.6
Bilirubin Total......2.6
Alkaline Phosphatase.106
ALT(SGPT)..............4  (said to be slightly low, vet says insignificant)
AST(SGOT)............185
Cholesterol...........92
Calcium.............12.3
Phosphorous..........2.2
Sodium...............134
Potassium............7.3  (out of a normal range of 2.4 to 4.7)
Chloride.............100
A/G..................1/1
Bun/Creatinine.........6
Globulin.............3.3
Carbon Dioxide........28
Lipase................21
Amylase...............10  (low, normal 25-600, vet says not significant)
Triglycerides.........28
CPK..................128
GGTP..................17
Magnesium............1.7
Anion Gap.............13
Osmolality, calculateed..272 (low, vet says OK, related to high K?)

Hemoglobin..........17.0
Hematocrit..........46.5
WBC..................7.8
RBC.................8.52
MCV...................55
MCH.................20.0  (slightly high, vet says not significant)
MCHC................36.6

Differential Absolute Percentage
Polys          5148      66%

Bands.......0......0%
Lymphs....2496....32%
Monos......156.....2%
EOS..........0.....0%
BASOS........0.....0%
Platelet Est    adequate
Anisocytosis    slight


My vet's response to this was:

"Mechanisms for Hyperkanemia:
 1.  Acidosis.  Not likely.  If acidotic would be after work or very sick
     metabolically.
 2.  Dehydration.  No evidence of this.
 3.  Tissue Damage.  Not likely.  No wounds.  No evidence of tying up.
 4.  Insulin Deficiency.  Not likely.  Glucose is normal.

 No evidence of hemolysis that the lab noted.  Can't explain why based on
 good condition of animal and relatively normal bloodwork otherwise."

I'm not going to lose sleep over this since my horse seems healthy
and happy, but it is a mystery that I would like to shed some light on.
Anybody ever see this before and know what it might mean?

Linda B. Merims
lbm@ici.net
Massachusetts, USA