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Single Biomarker

Bicarbonates (CO2)

Blood Bicarbonate (CO2)

This test measures the level of bicarbonate in your blood, which helps maintain the body's acid-base balance. It is commonly part of an electrolyte or metabolic panel and requires a simple blood draw.

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  • Free home collection
  • Physician-reviewed report

24 Hours

Turnaround

Blood

Sample

About This Test

What the Bicarbonates (CO2) test tells you

Bicarbonate is the body's main chemical buffer, and this test measures how much of it your blood is carrying. It is often reported as "CO2" on a results sheet, which causes understandable confusion: the label refers to total carbon dioxide content, and almost all of that is present as bicarbonate rather than as the gas you breathe out. It is a standard component of electrolyte and metabolic panels and is measured from the same blood sample as sodium, potassium and chloride.

Your body works within a narrow band of acidity, and bicarbonate is the buffer that defends it. Acid is produced continuously by ordinary metabolism, and bicarbonate neutralises it. Two organs then keep the system balanced: the lungs adjust how much carbon dioxide is exhaled, and the kidneys adjust how much bicarbonate is retained or discarded. Because these two systems compensate for one another, the bicarbonate value is read as part of a picture rather than as a standalone figure: it tells your doctor which direction the balance has shifted and often hints at whether the cause is metabolic or respiratory.

A fall in bicarbonate generally means acid is accumulating or bicarbonate is being lost. That happens in poorly controlled diabetes producing ketones, in situations where tissues are short of oxygen and generate lactic acid, in chronic kidney disease where acid cannot be excreted properly, and in prolonged diarrhoea, which flushes bicarbonate out through the gut. A rise usually reflects the opposite: acid lost through repeated vomiting, or bicarbonate retained by the kidneys to offset carbon dioxide that chronically lung disease prevents from being cleared. Neither direction is a diagnosis by itself, but both direct your doctor's attention efficiently.

Sample type
Blood
Measured in
mmol/L
Turnaround
24 Hours
Fasting
Not required
Best for
Adults & teens
Why Get Tested?

Doctors order this test to evaluate acid-base imbalances, monitor kidney function, and assess conditions such as diabetic ketoacidosis, chronic diarrhea, or respiratory failure.

  • Check acid-base balance

    Bicarbonate is the simplest routine blood measure of whether your body's acid-base regulation has drifted in one direction or the other.

  • Support kidney assessment

    The kidneys manage bicarbonate directly, so a persistently low level is one of the recognised signs that chronic kidney disease is affecting metabolism.

  • Investigate breathing and vomiting

    Long-standing lung disease and repeated vomiting both shift bicarbonate in characteristic directions, which helps explain an unwell patient's biochemistry.

  • Monitor known conditions

    In diabetes, kidney disease or diuretic treatment, tracking bicarbonate helps your doctor see whether management is keeping the balance stable.

When This Test Is Ordered

Reasons your doctor may request the Bicarbonates (CO2) test

Your doctor may order this test for any of the reasons below. Some are routine checks, others follow specific symptoms or an earlier result.

  • Routine electrolyte testing

    • Part of a routine electrolyte or metabolic panel during a general health check.

  • Fluid loss, diabetes & breathing

    • Poorly controlled diabetes, particularly with thirst, drowsiness or rapid breathing.
    • Prolonged vomiting or diarrhoea, or another cause of significant fluid loss.
    • Chronic lung disease, or unexplained breathlessness and confusion.

  • Kidney disease & medication

    • Known or suspected kidney disease being assessed or monitored.
    • Ongoing treatment with diuretics, antacids or other medicines that affect acid-base balance.
Preparation
The short version
No prep needed.
  • Blood
  • Free home collection
  • No fasting
  • Results in 24 Hours
  1. 1
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    No fasting window: pick any slot that suits you, online or on WhatsApp.

  2. 2
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    A DHA-licensed nurse collects your sample at home or in the office: free home collection.

  3. 3
    Results in 24 Hours

    A physician-reviewed, easy-to-read report lands securely by WhatsApp and email.

Prep note
Physician reviewed

No fasting is needed unless the bicarbonate is bundled into a panel that requires it.

Drink water as you normally would, since dehydration concentrates the blood and shifts electrolyte results. Avoid clenching and unclenching your fist during the draw, and let the phlebotomist release the tourniquet promptly, as prolonged pressure alters the local chemistry in the vein.

This is one test where prompt handling in the laboratory matters, because carbon dioxide escapes from a sample that stands too long, so an appointment where the sample can be processed without delay is preferable. Tell the team about diuretics, antacids, steroids, and any recent vomiting or diarrhoea.

Understanding Your Results

The Normal band, reported in mmol/L, means your acid-base balance is where it should be. A result in the Low band usually means acid is accumulating or bicarbonate is being lost: ketones in poorly controlled diabetes, lactic acid when tissues are short of oxygen, chronic kidney disease, prolonged diarrhoea or certain medicines, or the kidneys shedding bicarbonate to compensate for rapid breathing from anxiety, pain or fever. A result in the High band usually follows the opposite: acid lost through repeated vomiting, diuretics, dehydration or heavy antacid use, or bicarbonate held back by the kidneys to offset carbon dioxide retained in chronic lung disease. A sample left open or processed slowly loses carbon dioxide and reads falsely low. The result shows the direction of a shift, not its cause, so your doctor reads it with sodium, potassium and chloride, your medicines and symptoms.

SmartReport
2130
Healthy zone26mmol/LNormal
Reference ranges · mmol/L
Low
Low: may indicate metabolic acidosis.
10–21
Normal
Healthy acid-base balance.
22–29
High
High: may indicate metabolic alkalosis. Consult your physician.
30–40

Ranges are a guide: your physician interprets your result alongside your symptoms and history.

Reading a High or Low Result

  • What a higher result can point to

    • Repeated vomiting or loss of stomach contents, which removes acid from the body.
    • Diuretic treatment, which increases the loss of acid and chloride through the kidneys.
    • Chronic lung disease with retained carbon dioxide, prompting the kidneys to hold on to bicarbonate in compensation.
    • Excess mineralocorticoid activity, as in primary aldosteronism or certain adrenal disorders.
    • Significant dehydration, which concentrates the blood.
    • Heavy or prolonged use of antacids and other alkali-containing preparations.

  • What a lower result can point to

    • Ketone production in poorly controlled diabetes.
    • Lactic acid accumulation when tissues are short of oxygen, as in severe infection or circulatory failure.
    • Chronic kidney disease, where acid can no longer be excreted efficiently.
    • Prolonged diarrhoea, which loses bicarbonate directly through the bowel.
    • Rapid breathing from anxiety, pain, fever or altitude, with the kidneys compensating by shedding bicarbonate.
    • Certain medicines, including some used for glaucoma, epilepsy and migraine.

These are possibilities, not diagnoses. A single value outside the reference range is interpreted alongside your symptoms, history and other tests: your doctor decides what it means for you.

Limitations & Safety

What this test cannot tell you

  • Carbon dioxide escapes from a sample tube that is left open or processed slowly, which lowers the reported value artificially.
  • The result shows which direction the balance has moved but not the underlying cause, so it is read with the other electrolytes and the clinical picture.
  • It cannot separate a primary metabolic problem from the body's compensation for a breathing problem; that needs an arterial blood gas.
  • A value within the usual range does not exclude a disturbance where two opposing processes are cancelling each other out.

Risks of the blood draw

  • Mild bruising or brief soreness where the needle went in.
  • Occasional lightheadedness, which settles after a few minutes of rest.
  • Bleeding or infection at the site, which is rare with sterile single-use equipment.
Key Points
  • 1Reported as CO2, this test measures bicarbonate, the body's principal acid buffer.
  • 2The lungs and the kidneys jointly control it, so it reflects both systems.
  • 3A low value usually indicates acid accumulating or bicarbonate being lost.
  • 4A high value usually follows acid loss through vomiting or kidney compensation for retained carbon dioxide.
  • 5It is interpreted alongside sodium, potassium and chloride rather than on its own.
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Frequently Asked Questions

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The test reports total carbon dioxide content in the blood, and the great majority of that is carried as bicarbonate rather than dissolved gas. In practice the two labels are used interchangeably for this measurement, which is why the result sheet can be confusing.