Blood Tests For Acid-Base Disorders

Acidosis and alkalosis describe the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base). This imbalance is typically caused by some underlying condition or disease.

Normal blood pH must be maintained within a narrow range of 7.35-7.45 to ensure the proper functioning of metabolic processes and the delivery of the right amount of oxygen to tissues. Acidosis refers to an excess of acid in the blood that causes the pH to fall below 7.35, and alkalosis refers to an excess of base in the blood that causes the pH to rise above 7.45.

Acidosis occurs when blood pH falls below 7.35. It can be due to:

  • Increased acid production within the body
  • Consumption of substances that are metabolized to acids
  • Decreased acid excretion
  • Increased excretion of base

Alkalosis occurs when blood pH rises above 7.45. It can be due to:

  • Electrolyte disturbances caused by, for example, prolonged vomiting or severe dehydration
  • Administration or consumption of base
  • Hyperventilation (with increased excretion of acid in the form of CO2)

The absolute quantities of acids or bases are less important than the balance between the two and its effect on blood pH 

Any disease or condition that affects the lungs, kidneys, metabolism or breathing has the potential to cause acidosis or alkalosis. The normal balance between acid and base can be visualized in Figure 1.

The primary tests used to identify, evaluate, and monitor acid-base imbalances are:

  • Blood gases
  • Electrolytes

Blood gases 

It’s a group of tests together with an arterial blood sample (not vein). Results are like these.

Acid-Base Disorder pH HCO3 PCO2 Body Compensation
Metabolic acidosis Less than 7.35 Low Low Increased breathing rate (hyperventilation) to increase CO2 elimination
Metabolic alkalosis Greater than 7.45 High High Slowed breathing (hypoventilation) to decrease CO2 elimination
Respiratory acidosis Less than 7.35 High High Kidney increases retention of HCO3 and excretion of acid
Respiratory alkalosis Greater than 7.45 Low Low Kidney decreases retention of HCO3 and excretion of acid


It means Na+ (sodium), K+ (potassium), Cl (chloride), and bicarbonate (usually measured as total CO2 content).

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.