Normal bicarbonate levels

The Importance of Normal Bicarbonate Levels in Blood

A lot of physiological processes take place in the body to maintain a normal pH. Bicarbonate (a form of carbon dioxide) is a by product of the body’s metabolism. Blood carries bicarbonates to the lungs. This gets exhaled as carbon dioxide. Bicarbonates also get reabsorbed by the kidneys. The kidneys along with other organs of the body provide compensation for disturbances in pH of blood.

When acid accumulates in the body due to chronic respiratory illnesses or metabolic causes, the kidneys enhance urinary excretion of acid by increasing the plasma bicarbonate levels.

The primary of blood and buffers (buffer is a mixture of molecules which release or bind H+ in order to maintain a normal pH.) is to cause reaction of hydrogen (H+) ions with bicarbonate to form carbonic acid. This carbonic acid later dissociates to form CO2 and water.

Patients having disturbances in acid base balance present with effects of tissue malfunction due to abnormal pH or with a change in respiration pattern as a response to metabolic changes in the body.

A detailed history of the patient generally indicates an underlying cause such as uncontrolled diabetes mellitus or a chronic lung disease. Often, there are no symptoms and acid-base imbalance is only found on blood gas analysis. ‘Base Excess’ or ‘Base Deficit’ can also be calculated from the difference between patient’s bicarbonate levels and the normal levels.

Normal bicarbonate levels in blood: 23 – 30 mmol/L
Bicarbonate levels less than 23 or more than 30 are considered to be abnormal.
Normal pH level of blood: 7.35 – 7.45
Normal CO2 levels: 35 – 45 mm of Hg

How is it Measured?

A test for bicarbonate levels in the blood is also called as Carbon Dioxide Test (〖CO〗_2 test). An arterial or venous blood gas analysis is the commonly used technique for measuring bicarbonate levels in the blood.

What is the Importance of Bicarbonates?

  1. Bicarbonates are essentially alkaline in nature and are important in maintaining acid-base balance in the body.
  2. Maintenance of normal pH of blood.
  3. Maintains normal pH of the small intestine.
  4. Neutralizes the food that enters duodenum from the stomach.
  5. It has a preventive role against dental caries.
  6. Bicarbonates regulate the acid content of food such as proteins.
  7. A study conducting using mineral water containing sodium bicarbonate confirmed the absence of effect on blood pressure in hypertensive individuals.
  8. It helps to buffer lactic acid produced from exercise or in athletes.

Analysis of Bicarbonate Levels:

Imbalance pH HCO3 PCO2
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis

Abnormalities in Bicarbonate Levels:

Acidosis occurs when the lungs and kidneys are unable to maintain a normal blood pH. Excess acid accumulates resulting in a fall in plasma bicarbonate. Acidosis may be metabolic or respiratory, depending upon the cause.

    • Metabolic Acidosis occurs when the kidneys are unable to excrete excess acid. Some conditions that can cause metabolic acidosis are
      1. Uncontrolled Diabetes Mellitus – Lack of insulin and ketones can cause the pH to become acidic.
      2. Diarrhea and Vomiting result in excess loss of sodium bicarbonates.
      3. Renal Tubular Acidosis (RTA) – This condition should be suspected when there is no underlying gastrointestinal disturbance. Some causes of RTA are Wilson’s disease, myeloma, hyperparathyroidism, heavy metal toxicity, SLE, renal transplant rejection and certain drugs.
      4. Lactic Acidosis – Certain activities of the body cause break down of proteins releasing lactic acid. Conditions may be seizures, cardiac failure, liver failure and prolonged exercise or prolonged lack of exercise.
      5. Poisoning due to methanol, aspirin and ethylene glycol.


      1. Correction of the underlying cause of metabolic acidosis.
      2. Since metabolic acidosis is associated with dehydration and sodium depletion, suitable intravenous fluid replacement is done.
      3. Sodium bicarbonate and potassium bicarbonate are often used to correct Renal Tubular Acidosis (RTA).
    • Respiratory acidosis occurs when there is an excess of CO2 in blood. Respiratory acidosis can occur due to the following reasons
      • Excess alcohol consumption
      • Drug abuse
      • Obesity
      • History of accident or injury to the chest.
      • Chronic lung affections such as asthma and COPD.
      • Deformed shape of the chest.

      Management includes correction of causative factors. In severe cases, external ventilatory support (non-invasive ventilation) may be required.

Alkalosis occurs when there is an excess of bicarbonates in the blood or when an excess of acid gets excreted from the body. There is an increase in bicarbonate levels in the blood. Types of alkalosis are

    • Metabolic Alkalosis occurs due to the following causes:
      1. Hypovolemia – as from vomiting and diarrhea. This also occurs from diuretic drugs
      2. Excess of Corticosteroids – Cushing’s syndrome and hyperaldosteronism
      3. Overuse of antacids and laxatives
      4. Diuretic therapy


        1. For treatment of metabolic alkalosis due to hypovolemia, intravenous fluids are used to correct the acid basence
        2. Potassium to correct hypokalemia
        3. Treatment should focus on the underlying endocrine cause in normal volume metabolic acidosis
        4. Withdrawal or monitored doses of laxatives and antacids
    • Respiratory Alkalosis occurs when there is a prolonged duration of hyperventilation resulting in fall in blood CO2 and increase in pH.
      • Anxiety and hyperventilation result in respiratory alkalosis for a short duration.
      • It can be prolonged in case of pregnancy, chronic liver diseases, and pulmonary embolism or from certain drugs.
      • High altitudes.
      • High grade fever
      • Chronic or Acute lung diseases.

Management includes correction of the underlying cause, control of anxiety and in severe cases, non-invasive ventilation. Breathing into a paper bag helps in increasing CO2 levels.

Mixed Acid Base Disorders:

In some patients, there is a possibility of independent acid base imbalance to occur. In such situations, a normal blood pH with PCO2 and bicarbonate suggests a mixed acid-base disorder. This is not an uncommon occurrence.
Frequently, symptoms of the patient, medical history, physical examination and assessment of biochemical status indicate the underlying cause. Blood gas analysis is essential to understand the primary acid base imbalance.

What to Do If Cross the Normal Bicarbonate Level?

Bicarbonates are usually measured through blood gas examination. If any imbalance is noticed, it is important to correct them immediately as quite often. Those imbalances indicate a serious health condition.

      • Adequate hydration and a healthy diet help in maintaining normal bicarbonate levels in the blood.
      • Fruits rich in potassium help in preventing electrolyte imbalance.
      • Electrolyte replacement drinks should be used during and after exercise.
      • Breathing exercises and physical exercises help in maintaining a healthy condition.
      • Regular medications may be required in individuals with pre-existing diseases.
      • In diabetic individuals, control of blood sugar levels with the help of appropriate diet, exercise and medications.
Medically Reviewed By
Dr. Kaushal M. Bhavsar (MBBS, MD)Assistant Professor in Pulmonary Medicine, GMERS Medical College, Ahmedabad