How to Identify Respiratory & Metabolic Alkalosis

Alkalosis is a condition in which the arterial blood plasma is unusually alkaline. This typically means that the blood has an insufficient concentration of hydrogen ions. Alkalosis due to hyperventilation (increased respiration) is known as respiratory alkalosis. Alkalosis that results from a disorder of the metabolism is called metabolic alkalosis. You will need the results of several different blood tests in order to diagnose respiratory and metabolic alkalosis.

Submit a blood sample. A health care practitioner will take a blood sample from an artery. Arterial blood is needed because the blood must be fully oxygenated in order to for the partial carbon dioxide (pCO2) level to be meaningful. The blood sample will then be divided so that the laboratory can perform specific tests on separate portions of the blood sample.

Interpret the results of the pH test. The pH level is a simple measure of the acidity or alkalinity of the blood, but does not provide any information as to the cause of an abnormal reading. Blood normally has a pH between 7.35 and 7.45. A level below 7.35 indicates acidosis and a level above 7.45 indicates alkalosis.

Evaluate the pCO2. This is measure of the gas pressure in the blood that’s due to carbon dioxide and is typically measured in millimeters of mercury (mmHg). A normal value is between 35 and 45 mmHG. A pCO2 level below 35 mmHG may indicate respiratory alkalosis when accompanied by a pH greater than 7.45 and a normal HC03 level.

Assess the bicarbonate (HCO3) level. The concentration of HC03 is typically measured in millimoles (mM) with the normal range being between 22 and 26 mM. An HCO3 level above 26 mM may indicate metabolic alkalosis when accompanied by a pH greater than 7.45 and a normal pCO2 level.

Identify additional types of metabolic and respiratory alkalosis. A pCO2 level less than 35 mmHg and an HCO3 greater than 26 mM is known as combined alkalosis. A pCO2 level less than 35 mmHg and an HCO3 below 22 mM is known as partially compensated respiratory alkalosis. A pCO2 level greater than 45 mmHg and an HCO3 above 26 mM is known as partially compensated metabolic alkalosis.