Performance Characteristics
7-2
The handling of the blood outside the body provides many opportunities for error in
measurement technique.
The effect of the anti-coagulants is measured as a change in mean cell volume (MCV). Using MCV as
a correction standard eliminates the need to estimate and individually correct for the effect of the
concentration of EDTA or the sodium concentration of the anti-coagulant solution. The effect of
either on the in vitro erythrocyte can be significant.
Reference Standard for Hematocrit
When comparing CLM III data with other hematocrit determination techniques, there are several
considerations separate from MCV which are necessary to ensure that data is comparable and
consistent. For more information on Hematocrit accuracy see the Tech Notes Section on CRIT-LINE
Hematocrit Accuracy.
Reference Standard for Oxygen Saturation
The CLM is calibrated for oxygen saturation measurement using the IL-482/682 CO-
Oximeter (Instrumentation Laboratory, Inc., Lexington, MA) as the reference standard.
Using a standard other than the IL-482/682 CO-Oximeter may influence comparison
results. Abnormal patient states can also affect data. For more information on Oxygen
Saturation accuracy see the Application Guide Section on Oxygen Saturation Accuracy.
Hemoglobin Estimation
The CLM III monitor displays a hematocrit-based hemoglobin value. The monitor does NOT
actually measure hemoglobin; rather it calculates hemoglobin from the measured hematocrit value.
The following equation is used to calculate Hgb from the measured Hct value.
Hgb = HCT ÷ 2.94
General Precautions
Bubbles in a Sample: Air bubbles trapped in the CRIT-LINE Blood Chamber or in
the blood sample drawn for comparison will cause poor correlation between the CLM III
and the reference standard.
Abnormal [Na+] Levels: The CLM III was calibrated using blood samples from
patients with serum sodium levels of 137 mEq/L. Changes in [Na+] affect the micro
centrifuge-derived hematocrit values as follows: 1 unit decrease in “spun” hematocrit
per 12 mEq/L increase in [Na+]. Abnormal sodium concentration may occur due to:
Use of blood bank blood with sodium citrate (165 mEq/L)
Use of normal saline (0.9% NaCl) as diluent (154 mEq/L)
Over hydration (<137 mEq/L)
Hemolysis: Hemolysis may affect hematocrit determination, although no changes in CLM III measurements
have been noted for plasma hemoglobin levels below 5gm%.
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