Bicarbonate
Bicarbonate is your blood's natural buffer — it soaks up excess acid and stops your blood from becoming too acidic or too alkaline. Your kidneys and lungs keep it within a narrow range, and the result shows whether that balance is being kept. It is almost always read as part of a group of minerals rather than on its own.
Standard CareWhat is bicarbonate?
Bicarbonate (sometimes written as HCO₃⁻ or called total CO₂) is a chemical your body produces as a natural byproduct of making energy. As the RCPA explains, "bicarbonate is formed when your body uses oxygen to make energy." Once made, it travels in your blood to your lungs, where it is breathed out as carbon dioxide. Its main job is keeping your blood's pH — how acidic or alkaline it is — within the narrow range your cells need to work properly. The RCPA puts it plainly: "bicarbonate helps keep your blood from being too acidic or too alkaline. It acts like a sponge soaking up excess acid." When bicarbonate is low, the blood becomes more acidic (a process called metabolic acidosis); when it is high, the blood becomes more alkaline (metabolic alkalosis). Your kidneys and lungs regulate bicarbonate continuously to keep that balance steady.
Why is it tested?
Bicarbonate is part of the standard electrolytes panel alongside sodium, potassium, and chloride. Your GP may order it to assess kidney function, check for acid-base disturbances, or monitor a known condition affecting the kidneys or lungs. Because the acid-base balance and electrolyte balance are closely linked — as the RCPA notes, "changes in acid and alkaline levels in your blood, known as the acid-base balance, can affect electrolyte levels particularly those of potassium and bicarbonate" — reading bicarbonate as part of the group gives a fuller picture than any single result alone.
Reference range (Australia)
The AHRIA harmonised reference interval (AACB/RCPA-endorsed) applies to adults of all sexes. The range printed on your report may vary slightly between laboratories — use that range when reading your result.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A bicarbonate below the reference range means the blood is trending more acidic — doctors call this metabolic acidosis. The RCPA notes that "the less bicarbonate you have in your blood, the more acidic your blood becomes." Causes include kidney disease (which reduces the kidneys' ability to reclaim bicarbonate), uncontrolled diabetes, severe diarrhoea, and some medicines. Your GP will consider your other results — particularly creatinine and potassium — alongside the bicarbonate to understand what is driving the change.
A bicarbonate within the reference range, alongside normal sodium, potassium, and chloride, suggests your acid-base balance is well regulated. Staying well hydrated and keeping your GP informed of any new conditions or medicines helps maintain this balance over time.
A bicarbonate above the reference range means the blood is trending more alkaline than usual — doctors call this metabolic alkalosis. Common causes include significant fluid and salt loss from prolonged vomiting, the effect of some diuretics (fluid tablets), or conditions affecting the kidneys' ability to excrete bicarbonate. As the RCPA explains, "the more bicarbonate you have in your blood, the more alkaline your blood becomes." Your GP will look at your other electrolytes and the context of your symptoms to work out why.
What can affect your result
Your kidneys and lungs work together to maintain bicarbonate balance. The kidneys either reclaim bicarbonate from the urine or excrete it, depending on how acidic the blood is. The lungs regulate how much carbon dioxide (which the body converts from bicarbonate) is breathed out. Things that lower bicarbonate include kidney disease, uncontrolled diabetes, persistent diarrhoea (which causes direct bicarbonate loss from the gut), and some medicines. Things that raise it include prolonged vomiting (which removes acid from the stomach, leaving relatively more bicarbonate in the blood), some diuretics, and certain kidney conditions. The acid-base balance and electrolyte balance are tightly linked: potassium in particular tends to shift in the opposite direction to pH changes, so your GP will read bicarbonate and potassium together.
When to act
A bicarbonate outside the usual range is worth discussing at your next GP appointment rather than a cause for immediate concern in most cases. Your GP will look at it alongside the rest of your electrolytes — sodium, potassium, chloride — and your kidney markers (creatinine and urea), and decide whether a repeat test or further investigation is warranted. If you have symptoms such as unusual breathlessness (sometimes the body breathes faster to compensate for a change in blood acidity), significant fatigue, or nausea alongside the abnormal result, that is worth mentioning when you see your GP. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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