Bicarbonate Test

The bicarbonate test measures the amount of bicarbonate in a sample of blood. The test is also known as the HCO3 – test.

Bicarbonate is a base (a type of chemical) that helps the body maintain a normal balance between acids and bases. This balance prevents too much acid from accumulating in the body. Excess acid in the body fluids can lead to respiratory or metabolic acidosis (an excess build-up of acid in the body), which can be dangerous if left untreated. Usually, the kidneys and lungs help in eliminating acid from the body and maintaining the balance of bicarbonate in the blood. Therefore, this test helps doctors diagnose conditions that affect the body’s acid-base balance and decide on the most appropriate treatment.

The test is advised if you are experiencing the following symptoms of respiratory and metabolic acidosis:

• Fatigue
• Sleepiness
• Lethargy
• Rapid and deep breathing
• Confusion

The test is also highly recommended for the following categories of people:

• Individuals with chronic kidney disease (CKD): In these individuals, the kidneys cannot effectively remove acid from the body, which can lead to metabolic acidosis.
• Individuals with chronic lung disease: Individuals with lung disorders cannot remove enough carbon dioxide from their bodies by breathing.
• Pregnant women: During pregnancy, women experience respiratory alkalosis (low levels of carbon dioxide in the blood) and metabolic acidosis (excess acid in the body). These changes become more noticeable during labour and delivery.

The bicarbonate test alone cannot diagnose a condition, but it can be used with other tests to help diagnose and monitor conditions such as:

• Respiratory acidosis: This occurs when the body has too much carbon dioxide because it cannot remove enough of it by breathing.
• Metabolic acidosis: This condition occurs when the body produces too much acid. The kidneys cannot remove enough acid from the body.
• Diabetic acidosis: In this condition, substances known as ketone bodies accumulate in the body, typically in people with type 1 diabetes.
• Hyperchloraemic acidosis: This condition occurs when the body loses too much sodium bicarbonate, which can happen during diarrhoea.
• Lactic acidosis: This condition is characterised by the build-up of lactic acid in the body.
• Distal renal tubular acidosis: In this condition, the kidneys cannot remove enough acid into the urine, leading to acid build-up in the blood.
• Proximal renal tubular acidosis: In this condition, the kidneys cannot properly reabsorb bicarbonate, leading to an acid-base imbalance.
• Metabolic alkalosis: In this condition, there is an excess amount of bicarbonate in the blood. It usually occurs because of kidney diseases.
• Respiratory alkalosis: This occurs when too much carbon dioxide is breathed out, causing its level in the blood to drop. It can occur due to fever, low oxygen levels, or hyperventilation (fast breathing).

What to Expect Before the Bicarbonate Test

• No fasting is required for a standalone Bicarbonate test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise Bicarbonate levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

• A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Bicarbonate Test

• A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

In the bicarbonate test, the primary parameter being measured is:

• The level of bicarbonate in a sample of blood.

The HCO3 – normal range is indicated in the table below:

The table below provides a general interpretation of the bicarbonate test results based on whether the levels are low or high.

Like any other medical test, this test also has certain risks and limitations.

Risks:

• The bicarbonate test is generally safe and involves minimal risk. You may experience slight pain when the needle is inserted or mild bruising afterwards, which usually resolves spontaneously.

Limitations:

• Certain medicines can affect the test results. Please consult your doctor before you give the blood sample.
• The bicarbonate test alone cannot diagnose a medical condition. Other tests are required to confirm the underlying cause of the symptoms.

Depending on your symptoms and results, your doctor may recommend certain additional tests to better understand your condition. These may include:

• Basic metabolic panel
• Urine pH test
• Urine ketones test
• Blood ketones test
• Lactic acid blood test
• Chest X-ray
• CT abdomen
• Urinalysis