Abbott i-STAT 1, System Manual

Page: 552 / 658

Art: 714261-00E Rev. Date: 10-Jan-11
4
White Blood Cells
Interference from white blood cells depends upon the size of the cell. As an example, the hematocrit reading
will be increased by 1 %PCV when the white cell count is 50,000 per microliter, assuming the average white
blood cell occupies twice the volume of an average red blood cell.
Automated Hematology Methods
Osmolality:
16-27
Abnormal sample osmolality can create discrepant readings as the red cells shrink or swell to achieve
osmotic balance with the isotonic (normal osmolality) diluent. Differences up to 10 %PCV have been
reported for glucose concentrations in the range of 1000 mg/dL to 2000 mg/dL. Differences up to 5 %PCV
have been reported for samples with low or high sodium concentrations.
Cold Agglutinins:
28-32
Under the right conditions of diluent temperature, red blood cells from certain samples will clump together.
The large clumps will not be recognized as red blood cells by certain automated hematology analyzers, and
thus the overall red blood cell count and the calculated hematocrit, will be falsely low. In extreme cases, the
hematocrit can read low by up to about 8 %PCV.
Mean Cell Hemoglobin Concentration:
11-15
Red blood cells can deform under the pressure experienced when being sent through the measuring orifice.
This is particularly true for electrical impedance methods. Cells with lower hemoglobin concentrations will
deform to a greater degree. This can create errors as large as 3 %PCV.
Early authors attributed the discrepancy between automated hematology determinations and reference
microhematocrit determinations to variabilities in trapped plasma on the microhematocrit determination.
5-9,10a,10b
Recent authors have recognized the substance of the discrepancy to be an interference on the automated
method.
Co-oximetry Methods
The accuracy and precision of measured total hemoglobin from co-oximeters depends on the instrument’s
efficiency in hemolyzing the blood and the number of wavelengths used to determine hemoglobin. The
calculation of hematocrit from measured hemoglobin assumes a normal MCHC. Deviation from a normal
adult MCHC, e.g. in children, may give an inaccurate calculated hematocrit.
41
Other limitations of measuring
total hemoglobin by spectrophotometric methods include the effect of sulfhemoglobin and fetal hemoglobin
and hyperlipidemic plasma that may falsely elevate the hemoglobin.
42,43
An extremely high number of WBCs
may also elevate the hemoglobin value resulting in an inaccurately calculated hematocrit.
44