CLINICAL SIGNIFICANCE
Carbon dioxide levels are almost always measured as part of an
electrolyte panel to tell whether sodium, potassium, chloride, and
bicarbonate are in balance. They may be done as part of an annual
screen, included as part of a basic or comprehensive metabolic panel,
or done when there is a suspected imbalance. The CO2 test is also
done when evaluating acid-base balance, to screen for an imbalance,
and to monitor a known problem during treatment.
When CO2 levels are higher than normal (hypercapnia), it suggests
your body is having trouble maintaining its pH balance by releasing
excess carbon dioxide or that you have upset your electrolyte balance,
perhaps by losing or retaining fluid. Both of these imbalances may be
due to a wide range dysfunctions. CO2 rises with decreased alveolar
ventilation due to diseases of the lungs or bronchial tree, or breathing
CO2 enriched air. Depression of the overall lung capacity by certain
drugs may lead to retention of CO2. CO2 elevations may be seen with
chronic lung-related problems, such as emphysema, and metabolic
problems, such as severe diarrhea or prolonged vomiting (which can
cause metabolic alkalosis – an excessive loss of body acidity). Low
CO2 levels may be seen with respiratory alkalosis (which can be
caused by hyperventilation), metabolic acidosis, shock, starvation and
during kidney failure.
Regulation of the amount of carbon dioxide in blood is essential for
maintaining acid-base balance. CO2 is a major determinant of blood
pH because of its conversion to carbonic acid. As CO2 concentration
rises, so does hydrogen ion (H+) concentration.
STORAGE AND STABILITY(Note 3,5)
Reagents are stable until the expiration date on the label when stored
tightly closed at 2-8ºC, protected from light and contaminations
prevented during their use.
Do not use reagents over the expiration date.
Signs of reagent deterioration:
- Presence of particles and turbidity.
ADDITIONAL EQUIPMENT
- Spectrophotometer or colorimeter measuring at 415 nm.
- Thermostatic bath at 37º C (±0,1ºC).
- Matched cuvettes 1,0 cm light path.
- General laboratory equipment.(Note 1)
SAMPLES
- Serum or heparinized plasma.
QUALITY CONTROL
Control Sera are recommended to monitor the performance of assay
procedures: TBA / CO2 Control .
If control values are found outside the defined range, check the instrument,
reagent and calibration for problems.
Each laboratory should establish its own Quality Control scheme and
corrective actions if controls do not meet the acceptable tolerances.
REFERENCE VALUES4
Adults: 22-29 mmol/L
Infants 19,0-23,9 mmol/L
These values are for orientation purpose; each laboratory should establish its
own reference range.
PERFORMANCE CHARACTERISTICS
Measuring range: From detection limit of 5 mmol/L to linearity limit of 45
mmol/L. If the results obtained were greater than linearity limit, dilute the
sample 1/2 with distilled NaCl 9 g/L and multiply the result by 2.
INTERFERENCES5
The main interference in this assay is CO2 from the air or from the breath of
the analyst. Some drugs and other substances are also known to influence
blood CO2 levels. Haemoglobin up to a concentration of 1000 mg/dL does not
affect the assay. No conjugated bilirubin interference up to a concentration of
30 mg/dL. No free bilirubin interference up to a concentration of 60 mg/dL.
No lipid interference (trigs and intralipid) up to a concentration of 1200 mg/dL.
NOTES
1. In order to avoid contamination, it is recommended to use disposable
material.
2. Use clean disposable pipette tips for its dispensation.
3. Do not expose reagent to the air longer than necessary and store tightly
capped.
4. Do not pipette by mouth.
5. Do not shake reagent vigorously as this may cause excessive CO2
absorption.
6. SPINREACT has instruction sheets for several automatic.
Instructions for many of them are available on request.
