What does a low bicarbonate (CO2) level mean?

A low bicarbonate indicates metabolic acidosis — a build-up of acid in the body. Common causes include reduced kidney function (the kidneys normally remove acid), severe diarrhoea, and uncontrolled diabetes. Because the kidneys are central to acid-base balance, a low bicarbonate is often interpreted alongside your kidney function (eGFR and creatinine) and other electrolytes. Treatment depends on the cause and may include correcting the underlying problem or, in kidney disease, bicarbonate supplements.

What is bicarbonate on a blood test?

Bicarbonate, sometimes labelled CO2 or total CO2, measures the main buffer that keeps your blood's acid-base balance (pH) stable. It is controlled by the kidneys and lungs and is reported as part of the electrolyte or metabolic panel. Abnormal levels signal that the body has too much acid (low bicarbonate) or too little (high bicarbonate), which points your doctor toward causes such as kidney, lung, or digestive problems.

How is bicarbonate related to kidney disease?

The kidneys keep blood pH stable by removing acid and regenerating bicarbonate. When kidney function declines, acid accumulates and bicarbonate levels fall, causing metabolic acidosis — a common feature of chronic kidney disease. Low bicarbonate in CKD can contribute to bone and muscle problems and faster kidney decline, so doctors monitor it and may treat it with sodium bicarbonate to help protect the kidneys.

Do I need to fast for a bicarbonate test?

Bicarbonate is measured as part of an electrolyte or metabolic panel, which may require fasting only if other tests like glucose are included. Bicarbonate itself does not require fasting. One practical point: blood samples exposed to air can lose CO2 and give a slightly low reading, so labs process them promptly. Follow your lab's instructions and mention any vomiting, diarrhoea, or medications that could affect the result.

Understanding Your Bicarbonate (CO2) Blood Test Results

Quick answer: Bicarbonate (sometimes shown as CO2 or “total CO2” on a panel) reflects your body’s acid-base balance — how well acids and bases are kept in equilibrium. The kidneys and lungs control it. A low bicarbonate can mean metabolic acidosis (too much acid), which is common in reduced kidney function; a high level can mean the opposite. It is read with your other electrolytes and kidney function.

Bicarbonate is the quiet member of the electrolyte panel, but it tells your doctor something important: whether your body’s acid-base balance is steady. Because the kidneys are central to that balance, an abnormal bicarbonate often ties back to kidney function.

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Bicarbonate Reference Range

Result	Interpretation
~22–29 mmol/L	Normal range (varies by lab)
Low	Metabolic acidosis — too much acid (common in reduced kidney function, diarrhoea, uncontrolled diabetes)
High	Metabolic alkalosis — too little acid (vomiting, some diuretics)

The Kidney Connection

Healthy kidneys remove acid and regenerate bicarbonate to keep the blood’s pH stable. As kidney function declines (a falling eGFR), acid can build up and bicarbonate falls — a state called metabolic acidosis that is common in chronic kidney disease. Treating low bicarbonate (sometimes with sodium bicarbonate) can help protect the kidneys and bones, which is why it is monitored in CKD.

Helpful for this appointment

home blood pressure monitor — blood pressure control is central to protecting kidney function
appointment notebook — to track your kidney and electrolyte results over time

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Questions to Ask Your Doctor

Is my bicarbonate low or high, and what does that suggest?
Is it related to my kidney function?
Do I need treatment to correct it?
How does it fit with my other electrolytes?
How often should it be checked?

Regional Notes

Singapore: Part of the standard electrolyte/renal panel at all labs.

Australia: Included in urea-and-electrolytes (U&E) testing.

United States: Reported as CO2 within the basic/comprehensive metabolic panel.

KEY SOURCES

RELATED GUIDES

📊 See the full chart: compare this with typical adult ranges for common tests in our Blood Test Normal Ranges reference chart.

Medical Disclaimer: This guide is for informational and preparation purposes only. It does not constitute medical advice, diagnosis, or treatment. Always consult a qualified medical professional for guidance specific to your situation.