EmpeiriaCarbon dioxide, total
Also known as
bicarbonate, HCO3, CO2
CHO₃⁻ inorganic ion
What this substance is
- formula
- CHO₃⁻
- mass
- 61.016 g/mol
- monoisotopic
- 60.99312
- charge
- -1
- InChIKey
- BVKZGUZCCUSVTD-UHFFFAOYSA-M
- ChEBI
- CHEBI:17544
Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.
3D model · Carbon dioxide, total
Generated by RDKit from ChEBI's verified structure, and accepted only because its own 3D geometry reproduces ChEBI's InChIKey. A flexible molecule takes many shapes; this is one low-energy one. Drag to rotate, scroll to zoom.
Reference ranges
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This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.
How it is measured
In practice
A health worker takes a small blood sample from a vein in your arm with a needle. It usually takes less than five minutes. Some medicines can raise or lower the result, so tell your provider what you take. This test is often part of a larger blood panel.
Often run within a BMP or CMP. Anaerobically collected venous blood is preferred; serum or lithium heparin plasma is acceptable. Handling matters: bicarbonate in uncapped tubes falls by about 4 mmol/L within an hour, and refrigerated shipping in serum separator tubes can lower results. Some prescription and over-the-counter medicines alter the value.
Before the test
- Tell your provider about everything you take, but do not stop any medicine unless your provider tells you to.
- Fast (no food or drink) for several hours only if your provider has ordered other tests that need it.
Where: laboratory
Sources: Carbon Dioxide (CO2) in Blood, MedlinePlus (U.S. National Library of Medicine); NHANES 2017-2018 Laboratory Procedure Manual, Bicarbonate (CDC National Center for Health Statistics) cited · not yet checked by a person
In the lab
PEP carboxylase / malate dehydrogenase (enzymatic)
Most carbon dioxide in blood is carried as bicarbonate. The machine uses helper proteins that need bicarbonate to work, and as they work a coloured chemical fades. The faster it fades, the more bicarbonate there is.
Phosphoenolpyruvate carboxylase uses bicarbonate to convert phosphoenolpyruvate to oxaloacetate, which malate dehydrogenase reduces to malate while oxidising an NADH analogue; the rate of absorbance fall at 415 nm is proportional to bicarbonate.
- Read by: Rate of NADH-analogue absorbance decrease at 415 nm
What can throw it off
- High ambient CO2 in the laboratory (falsely high)
- IgM gammopathy (rare)
Sources: Koerbin G et al. Bias Assessment of General Chemistry Analytes using Commutable Samples. Clin Biochem Rev 2014;35:203-211 (PMC4310060); NHANES 2017-2018 Laboratory Procedure Manual, Bicarbonate, CDC/NCHS cited · not yet checked by a person
What it reports on
-
nephron tubule
regulated by
The kidneys help keep blood bicarbonate, which is most of total CO2, at a normal level.
-
lung
regulated by
The lungs breathe out carbon dioxide, so lung function also affects blood CO2 levels.
Associated symptoms
Conditions this marker features in
-
either
Low blood potassium
· supportive
Bicarbonate is part of the first-line work-up. Some causes come with a high level (metabolic alkalosis), others with a low one (metabolic acidosis).