By The Pawline veterinary teamVeterinary-reviewed by Alastair Greenway, BVM&S MRCVS · 25 July 2026
Bicarbonate is the body's main buffer against acid, so total CO₂ on a chemistry panel is essentially a measure of acid-base balance. A low value usually means metabolic acidosis — acid accumulating or bicarbonate being lost — which is common in kidney disease, diabetes and severe diarrhoea.
The body works within a very narrow pH range, and bicarbonate is its principal buffer — the chemical sponge that mops up acid. On most chemistry panels this is reported as total CO₂ (TCO2), which is very nearly all bicarbonate. So although it looks like a gas measurement, TCO2 is best read as "how much buffer is left", and therefore as a window onto acid-base balance without needing a formal blood-gas analysis.
Bicarbonate is the body's main buffer against acid, so total CO₂ is essentially a measure of how much buffering capacity remains.
Reading a low result
A low bicarbonate/TCO2 indicates metabolic acidosis — the buffer is being consumed or lost faster than it is replaced. The common causes group neatly:
Acid accumulating: chronic kidney disease (failing to excrete acid — a very common cause), diabetic ketoacidosis (ketones are acids), lactic acidosis from poor tissue perfusion or shock, and certain toxins (notably antifreeze poisoning).
Bicarbonate being lost: severe diarrhoea, which sheds bicarbonate-rich intestinal fluid, and some kidney tubular disorders.
Metabolic acidosis matters clinically — it affects heart function, breathing (the body compensates by breathing faster to blow off CO₂), and how a patient feels. Marked acidosis is corrected as part of treating the underlying cause, and it is one of the disturbances that makes a sick patient sicker.
Reading a high result
A high bicarbonate indicates metabolic alkalosis — most classically from persistent vomiting of stomach contents, which loses acid (and chloride) from the body. This is why bicarbonate is read alongside chloride: the pattern of a low chloride with a high bicarbonate is a recognisable signature of gastric vomiting. Some diuretics can produce it too.
In chronic disease
Bicarbonate is followed in chronic kidney disease, where a progressive metabolic acidosis develops as the kidneys lose the ability to excrete acid, and where correcting it can improve how a patient feels and may help slow progression. It is also monitored during treatment of diabetic ketoacidosis, where a rising bicarbonate is a key sign the crisis is resolving. In both, the trend is an objective marker of whether treatment is working.
Cat vs dog
Bicarbonate is interpreted identically in both species, with similar reference intervals. Chronic kidney disease is a leading cause of low bicarbonate in each — with particular frequency in older cats given how common feline CKD is — while vomiting-driven alkalosis occurs in both.
About the reference range and sample handling
This page shows no range strip. Pawline draws a band only where it holds a verified reference interval, and TCO2 intervals are method-specific. Handling matters: because CO₂ escapes from a sample exposed to air, a tube left open or under-filled reads falsely low. A blood gas analysis gives the fuller acid-base picture (including pH and respiratory contribution) where that detail is needed. Read your result against the range on your own report.
For orientation only, one published example: Cornell University's veterinary laboratory reports total CO₂ of roughly 14–24 mEq/L (≈14–24 mmol/L) in dogs and 14–20 mEq/L in cats. That is one laboratory's figure on one analyser — your own report's range is what counts.
What to do next
A low bicarbonate is a prompt to identify the acidosis's cause with your vet — kidney function, glucose and ketones, and perfusion being the first considerations — rather than a finding to treat in isolation. A high bicarbonate, especially with a low chloride, points towards loss of stomach acid from vomiting. In both directions, it is the underlying condition that is treated, with the bicarbonate followed to confirm recovery.
This page is educational and is not a diagnosis. Lab results are interpreted in the full clinical context by your veterinary surgeon; a single value rarely tells the whole story.
