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Total carbon dioxide measured by the Vitros enzymatic method
A Frezzotti1, A M Margarucci Gambini, G Coppa
1Laboratorio di Analisi Chimico Cliniche e Microbiologiche, Azienda Ospedaliera Umberto I-Torrette, Ancona, Italy.
Clinical Chemistry and Laboratory Medicine
|May 22, 1998
Summary
The Vitros enzymatic method accurately measures serum total carbon dioxide (tCO2) in venous blood. However, it should not replace calculated arterial bicarbonate due to significant discrepancies, preventing misinterpretation and treatment errors.
Area of Science:
- Clinical Chemistry
- Biochemistry
Background:
- Accurate determination of total carbon dioxide (tCO2) is crucial for acid-base balance assessment.
- Enzymatic dry chemistry methods offer potential advantages in tCO2 measurement.
Purpose of the Study:
- To evaluate the performance of an enzymatic dry chemistry method for serum tCO2 determination using the Vitros 500 analyser.
- To assess the method's accuracy, linearity, interference, and agreement with calculated bicarbonate values.
Main Methods:
- Performance evaluation of the Vitros 500 analyser for serum tCO2 using an enzymatic dry chemistry method.
- Assessed imprecision, linearity, and interference from hemoglobin and bilirubin.
- Compared venous serum tCO2 results with calculated arterial bicarbonate (HCO3-) values.
Main Results:
- The Vitros tCO2 method demonstrated acceptable imprecision and linearity (r=0.99) within the 5.5-39.2 mmol/l range.
- Hemoglobin did not interfere, but bilirubin above 30 µmol/l caused significant dose-dependent underestimation.
- A poor agreement (r=0.58) was observed between Vitros venous tCO2 and calculated arterial bicarbonate, with a mean difference of 5.48 mmol/l.
Conclusions:
- The Vitros enzymatic method reliably measures serum tCO2 in venous samples.
- This method is not interchangeable with calculated arterial bicarbonate, to prevent clinical confusion and therapeutic errors.