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What is Bicarbonate test?

Bicarbonate, a form of carbon dioxide (CO2), is an electrolyte that helps in maintaining acid-base balance, and thereby the pH, in body. Bicarbonate test, also known as total CO2, TCO2, CO2 content, bicarb, and HCO3-, detects the total amount CO2 in blood, which is present in the form of bicarbonate. CO2 is the primary by-product of many metabolic processes. So, this test is done as a part of the basic metabolic panel, electrolyte panel or comprehensive metabolic panel to detect and monitor the imbalance in electrolyte levels or acid-base content in body, e.g., excess of acid or base (acidosis or alkalosis, respectively).

Bicarbonate test is generally recommended with other tests such as sodium, potassium and chloride tests. Blood gases test may also be ordered to identify the severity of the imbalance.

  1. Why is Bicarbonate test performed?
  2. How do you prepare for Bicarbonate test?
  3. How is Bicarbonate test performed?
  4. What do Bicarbonate test results mean?

Bicarbonate test helps in detection of an imbalance of acid and base in the body. Kidneys and lungs are primarily involved in pH regulation in the body by eliminating the excess bicarbonate. Lungs remove excess CO2 along with exhalation while kidneys help flush out excess acids in urine. Raising or lowering the respiratory rate can thus affect acid-base balance within minutes. Medical conditions effecting lung and kidney function also leads to acid-base imbalance. Some conditions, in which, bicarbonate test is advised include heart failure, blood pressure fluctuations, and liver and kidney disease.

A bicarbonate test is typically recommended in individuals experiencing the following symptoms:

This test may also be recommended at specific intervals when the individual has some disease or is taking some medication that has a tendency to affect the acid-base balance in body. Another blood test that measures carbon dioxide is blood bases.

Although bicarbonate test does not need any special preparation, a doctor may recommend stopping certain medicines before the test as these medicines may interfere with test results. Do not stop or change the course of any medication without consulting a doctor.

Eating fruits with high acid content can also affect bicarbonate test results. Inform the doctor about any medicines, vitamins, herbs and supplements that you take.

Medicines that lead to an increase in bicarbonate levels include steroids, bicarbonates, barbiturates, loop diuretics, fludrocortisone and hydrocortisone.

Medications that lower bicarbonate levels include tetracycline, methicillin, nitrofurantoin, thiazide diuretics and triamterene.

Blood is withdrawn from a vein in the arm (on the back of the hand or the inside of the elbow) by inserting a needle.

Though it is a completely safe and harmless procedure, some risks of blood collection with a needle include bleeding, bruising, infection and lightheadedness. Also, slight pain is felt at the site of needle insertion, and throbbing and mild soreness is experienced at the site after withdrawing blood.

The normal range of bicarbonate in blood is 23 to 29 millimoles per litre (mmol/L) or milliequivalents per litre (mEq/L). This range may slightly vary in different laboratories due to the type of instruments used.

Bicarbonate levels that are higher or lower than normal indicate the presence of an underlying condition that disrupts the maintenance of acid-base balance in body. Some conditions that may lead to a reduction in bicarbonate levels are:

  • Chronic diarrhoea
  • Kidney disease
  • Shock
  • Addison disease, an adrenal gland condition
  • Metabolic acidosis (decreased bicarbonate level in the blood)
  • Aspirin overdose
  • Methanol poisoning
  • Diabetic ketoacidosis (high levels of acids called ketones in the blood)
  • Ethylene glycol poisoning

Some conditions that cause a rise in bicarbonate levels are:

Regardless of what the results say, it is important to contact a  doctor for correct interpretation and diagnosis of the health condition.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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  1. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Bicarbonate
  2. Lechtzin, N. (@ 2015). Exchanging Oxygen and Carbon Dioxide. Merck Manual Consumer Edition. [internet]
  3. Robinson MT, Heffner AC. Acid-base disorders. In: Adams JG, ed. Emergency Medicine. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 160.
  4. Seifter JL. Acid-base disorders. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 118.