Intended Use
For quantitative determination of Carbon Dioxide content in human plasma or serum. The plasma CO2 is decreased in metabolic acidosis and respiratory alkalosis, whereas the plasma level of CO2 is increased in metabolic alkalosis and respiratory acidosis(1-3).

Assay Principle
This enzymatic assay of CO2 is based on two coupled enzyme reactions including phosphoenol pyruvate carboxylase (PEPC) and malate dehydrogenase (MDH). PEPC catalyses the first reaction which produces oxaloacetate. In the presence of MDH, NADH is oxidized by oxaloacetate to NAD+. This results in a decrease in absorbance at 340 nm that is directly proportional to CO2 concentration in the sample.

Phophoenolpyruvate +HCO3-    ----PEPC+Mg++ -----> Oxaloacetate +H2PO4

Oxaloacetate +NADF ----MDH----> Malate +NAD+

Specimen Collection and Handling
Serum or heparinized plasma may be assayed. Ideally, venous blood should be collected and handled anaerobically. Do not use EDTA, citrate or oxalate as anticoagulant.
Plasma and serum, after prompt separation from cells or clot, should be kept tightly stoppered.
CO2 content of blood is stable for 1 hour when stored at 2 – 4 °C under anaerobic conditions.

Warnings
1. For in vitro diagnostic use.
2. Specimens and reagents containing human sourced materials should be handled as if potentially infectious, using safe laboratory procedures such as those outlined in Biosafety in Microbiological and Biomedical Laboratories (HHS Publication Number [CDC] 93-8395).
3. As with any diagnostic test procedure, results should be interpreted considering all other test results and the clinical status of the patient.
4. Avoid swallowing and contact with skin or mucous membranes.

Instructions For Reagent Handling
For BQ007EAEL
CO2 reagent is a ready-to-use single liquid reagent. Unopened reagent is stable until the expiration day. Opened bottles stored in the closed tightly stoppered or typed bottles are stable for 1 day at room temperature and 7 days at 2 – 4 °C. Do not use the reagent if the absorbance of the reagent itself is less than 1.3 at 340 nm against water.
Reagents from different lots must not be interchanged.

Normal range
Normal value of CO2 in serum or plasma is 22-29 mmol/L for adults, and 19.0-23.9 mmol/L for infants.
It is strongly recommended that each laboratory establish an expected range characteristic for the local population.

Interfering Substances
No significant interference (less than 10% deviation) was observed when tested on Cobas Mira at the indicated concentrations. Bilirubin: 40 mg/dL; Intralipid: 1000 mg/dL; hemoglobin: 600 mg/dL; ascorbic acid: 10 mg/dL.

Linearity
The assay is linear upto 40 mmol/L. If the concentration exceeds 40 mmol/L in serum or plasma, dilute serum or plasma with 0.9% NaCl before assaying. Multiply result with the dilution factor for final result.

Assay Accuracy
The assay has intra %CV of 4.3%, and inter %CV of 5.2%.

Precautions
1. The reagent contains <0.1% sodium azide, NaN3, as preservative. Sodium azide may react with lead and copper plumbing to form highly explosive metal azide. On disposal, flush with a large volume of water to prevent azide buildup.
2. Avoid contamination of the reagent with CO2. Do not blow into pipette, since breath contains a high content of CO2. Do not let bottles open unnecessary, since CO2 from air can contaminate the reagent. Keep container tightly stoppered.
3. Do not use the reagents after the expiration date labeled on the outer box.

Instrument Parameter Settings
Cobas Mira Parameters
Measurement Mode              Absorb
Reaction Mode                     R-S
Calibration Mode                 Slope Avg
Reagent Blank                      Reag/DIL
Cleaner                                No
Wavelength                          340 nm
Decimal position                   3
Sample cycle                        5
Sample volume                    2.0 uL
Sample dilution                    H2O
Dilution volume                   10.0 uL
Reagent cycle                       1
Reagent volume                 350 uL
Calibration
Sample limit                        No
Reaction direction              decrease
Conversion factor              1.0000
Offset                                0.0000
Test range Low                 0.000 mmol/L
Test range High                 9999.00 mmol/L
Number of steps                1
Calc. Step A                     End-point
Readings first                     T2
Readings last                      12
Calibration
Calibration interval             Each day
Time                                  No
Blank
Reagent range       Low     -0.1
                            High       2.7
Blank range          Low      -0.1
                            High       0.1
Standard pos                       1
Standard-1                        30.000 mmol/L
Standard-2                         No
Control
CS1 pos                            No
CS2 pos                            No

References
1. Tietz, N. W. (Ed): Fundamentals of Clinical Chemistry, W. B. Saunders Co., Philadelphia, 865 (1982)
2. Contarow and Trumper, Clinical Biochemistry, 7th ed., Al Latner, Editor, Saunders, Philadelphia, p. 399 (1975)
3. Clinical Chemistry, LA Kaplan, AJ Pesce, Editors, CV Mosby Company, St. Louis (MO), p. 1056 (1984)