Carbon dioxide (CO2) is a gaseous waste product from metabolism. The blood carries carbon dioxide to your lungs, where it is exhaled. More than 90% of carbon dioxide in your blood exists in the form of bicarbonate (HCO3). The rest of the carbon dioxide is either dissolved carbon dioxide gas (CO2) or carbonic acid (H2CO3). Your kidneys and lungs balance the levels of carbon dioxide, bicarbonate, and carbonic acid in the blood.
This test measures the level of bicarbonate in a sample of blood from a vein. Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.
Bicarbonate is not usually tested by itself. It may be done on a blood sample taken from a vein as part of a panel of tests that looks at otherelectrolytes, such as sodium, potassium, and chloride. It can also be done as part of an arterial blood gas (ABG) test. For the arterial blood gas study, the blood sample is taken from an artery.
Regards
http://www.ncbi.nlm.nih.gov/pubmed/15065646
http://www.webmd.com/a-to-z-guides/bicarbonate
Urine bicarbonate is virtually never measured anymore as part of the work up for the RTAs. When the blood urine pCO2 difference was key to differentiating various forms of RTA, clinician on occasion would measure urine PCO2 and Urine HCO3 under mineral oil that was itself pre equilibrated with 5% CO2 to prevent loss of CO2 from the sample. The measurements had to be done ASAP (within an hour by the laboratory)
Thank you for you answers.
One more question: do you think that is possible to use standard bedisde blood gas and electrolyte analyzers for measuring urine pCO2?
For pCO2 yes
HCO3 van be estimated from the pH and pCO2. since HCO3 is no longer measured by the van slyke method, I do not know the accuracy of the HCO3 using electrolyte analyzers where the HCo3 is measured through a linked enzymatic reaction
we have measured urine pH and PCO2 using a clinical laboratory blood gas analyzer and calculated urine HCO3 from these results. The blood gas analyzer can be re-calibrated to a lower pH of the urine to give more accurate results; however there are some extremes of urine pH ie 4 or 9 not seen in blood and even with re-calibration, the blood gas analyzer results will not be close to these values giving some error. Also the warranty for the blood gas analyzer does not extend to testing urine samples with extreme pH deviation. So you might be best to use specific electrodes for pH and PCO2 that can be calibrated to the pH range of your samples rather than clinical grade blood gas analyzers.
