Page 177 - Basic Monitoring in Canine and Feline Emergency Patients

bromide as an anti-epileptic, the extra sodium can increase potassium levels. In general, the potas-
elevate the measured sodium levels. Potassium sium content of red blood cells in most veterinary
VetBooks.ir bromide (a cation with a single positive charge species is low enough to not cause clinically sig-
nificant changes in potassium levels, but wide-
similar to sodium) may also be interpreted by the
machine as sodium and falsely elevate blood
from dog breeds such as the Akita which contain
sodium levels. If a blood sample is drawn from a spread hemolysis or hemolysis of red blood cells
sampling IV line that has not had an appropriate higher than normal amounts of potassium might
waste sample drawn first, there may be significant cause clinically significant alterations in potas-
hemodilution of the sample with excessive lactated sium levels.
Ringer’s solution or 0.9% saline or there can be Platelets and white blood cells can also leak potas-
in vitro dilution of a blood sample with isotonic sium into plasma with prolonged storage; this is
crystalloid fluids. In both situations, the sodium in generally not an issue unless there are excessively
the isotonic crystalloid solutions can falsely large numbers of cells as in thrombocytosis (typi-
increase sodium levels. cally >500,000 cells/hpf) and leukocytosis (>70,000
In contrast, any molecule that increases serum cells/hpf). In addition, potassium release from both
osmolality (β-hydroxybutyrate, glucose, mannitol, white blood cells and platelets during activation and
lactate) can decrease sodium concentrations by coagulation in prolonged storage conditions can
drawing more water into the plasma compartment lead to hyperkalemia in states of leukocytosis and
where the sample is measured, even though the total thrombocytosis. Normally platelet activation leads
body content of sodium may be normal. See Further to increases in serum potassium that are generally
Reading section readings for more information 0.3–0.5 mmol/L greater than plasma, but these dif-
about mathematical correction factors for sodium ferences can be significantly increased with pro-
in states of hyperosmolality. found thrombocytosis. Conversely, leukocytes can
also absorb potassium, which may falsely lower
levels if the patient has a profound leukocytosis or
Potassium
leukemia.
When using flame photometric methods to meas-
ure potassium, both lipemia and hyperproteine-
mia can potentially increase the non-aqueous Calcium
proportion of the blood, leading to a false
decrease in the serum potassium concentrations Total calcium
similar to that seen with sodium (see above for Total calcium is measured via colorimetric meth-
mechanism). ods where a dye (orthocresolphthalein complex-
Potassium levels have also been shown to falsely one or Arsenazo III) complexes with calcium and
decrease with ion-specific electrodes when triglycer- causes a color change. Therefore, anything that
ide levels are higher than 650 mg/dL due to dilution falsely alters the degree of color change by binding
of the sample with the potassium-free triglyceride to the dye can falsely elevate total calcium levels.
component. Ion-selective electrode measurement of This would include lipemia and hemolysis.
potassium can also be decreased when there is con- However, hyperbilirubinemia will falsely decrease
tamination of the sample with fluids that contain calcium levels by binding to the calcium and not
little to no potassium (0.9% sodium chloride, allowing calcium to complex with the dye. Use of
lactated Ringer’s solution) or when osmotically anticoagulants such as EDTA, citrate, or oxalate can
active particles such as mannitol draw water into bind calcium, lowering the total calcium measure-
the intravascular compartment. ments. Thrombocytosis can also falsely increase
Potassium can be falsely elevated when using total calcium levels in serum due to release of cal-
ISE or flame photometric testing. Anything that cium during clotting.
leads to cellular rupture and release of potassium In addition, since total calcium levels include
into the sample can falsely elevate the potassium. the calcium that is protein bound, changes in pro-
This would include hemolysis due to placing sam- tein concentration (primarily albumin) will alter
ples on ice for prolonged periods and significant measured total calcium levels. Therefore, hypoal-
delays in testing after sample collection. Similarly, buminemia will cause a decreased total calcium
hemolysis induced by blood collection could level. Similarly, if levels of albumin are elevated,

Electrolyte Monitoring 169