xvi
Limitations of the Procedure
A number of substances have been reported to cause physiological changes in blood, serum, and
plasma analyte concentrations. A comprehensive discussion concerning these and other interfering
substances, their blood, serum or plasma concentrations and their possible physiological involvement
is beyond the scope of this method sheet. No significant effect on serum and urine has been demon-
strated from bromide, ammonium and iodide.
As with any clinical reaction, users must be alert to the possible effect on results due to unknown
interference from medications or endogenous substances. All patient results must be evaluated by
the laboratory and the physician in light of the total clinical status of the patient.
Opening and closing the fist with a tourniquet in place results in an increase in potassium levels by as
much as 10 to 20%. It is recommended that the blood sample be obtained without a tourniquet, or
that the tourniquet be released after the needle has entered the vein and 2 minutes elapsed before the
sample is drawn.
Since the concentration of potassium inside erythrocytes is much greater than that in extracellular
fluid, hemolysis should be avoided, and the serum should be separated from the cells as soon as
possible after collection.
The lithium electrode response is dependent on the actual sodium concentration of the sample. The
AVL 9180 Analyzer reports lithium in the range of 105 - 180 mmol/L Na
+
.
Interferences
Salicylate, in extremely high levels, is known to interfere with the chloride electrode and results in a
positive bias of the chloride result. At therapeutic levels of salicylate concentration, the influence on
chloride is clinically insignificant.
The lithium electrode shows a slight sensitivity to the ionized calcium present in the sample and
results in a negative bias of the lithium result. At normal physiological ionized calcium concentra-
tions, the influence of ionized calcium is clinically insignificant.
5
Kost GJ.Arch.Path.Lab.Med., Vol.117, Sep.1993, p.890-95
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