An abnormal level of one blood gas alone is often not enough to make a diagnosis. In combination, these levels can indicate the conditions below (for definitions of these measurements see About arterial blood gas (ABG) tests).

• Impaired respiratory function. Low PaO2, O2CT and SaO2 levels, combined with high PaCO2, are an indication of impaired respiratory function, which may be caused by the following:
  
  
• • Weakness or paralysis of the diaphragm (the muscle that inflates and deflates the lungs)
    
    
  • Airway obstruction
    
    
  • Brain injury
    
    
  • Brain tumor
    
    
  • Drug abuse
    
    
  • Asthma or emphysema
    
    
  • Near drowning
    
    
• Insufficient oxygen intake. Low PaO2, O2CT and SaO2 levels combined with normal PaCO2, are an indication of impaired oxygen intake, which may be caused by:
  
  
• • A shunt that allows blood to bypass the lungs
    
    
  • Collapsed lung
    
    
• Insufficient blood oxygen levels. Low O2CT levels combined with normal PaO2, SaO2 and PaCO2 are an indication of insufficient blood oxygen levels, which may be caused by:
  
  
• • Severe anemia (deficiency of red blood cells)
    
    
  • Decreased blood volume
    
    
  • Decreased ability of red blood cells to carry oxygen
    
    
• Respiratory acidosis. A low pH combined with high HCO3 and PaCO2 is an indicator of respiratory acidosis. Symptoms include slow and shallow breathing (hypoventilation), headache, rapid heartbeat (tachycardia), confusion, restlessness and apprehension. This may be caused by:
  
  
• • Lung disease, such as pneumonia or chronic obstructive pulmonary disease (COPD)
    
    
  • Suffocation or an obstructed airway
    
    
  • Drug abuse
    
    
  • Injury, surgery or other trauma
    
    
  • Heart disease, lung disease or neuromuscular disease
    
    
• Respiratory alkalosis. A high pH combined with low HCO3 and PaCO2 is an indicator of respiratory alkalosis. Symptoms include rapid and deep breathing (hyperventilation), prickling or tingling of the skin, lightheadedness, twitching, anxiety and fear. This may be caused by:
  
  
• • Lung disease, such as asthma or pneumonia
    
    
  • A bacterial infection
    
    
  • Drug or alcohol abuse
    
    
  • Injury or trauma
    
    
  • Pain
    
    
  • Fever
    
    
  • Liver failure
    
    
  • Severe anxiety
    
    
  • Improper settings on a ventilator
    
    
• Metabolic acidosis. A low pH combined with low HCO3 and PaCO2 is an indicator of metabolic acidosis. Symptoms include rapid and deep breathing (hyperventilation), headache, sweet-smelling breath, unusual tiredness or weakness, drowsiness, prolonged unconsciousness (coma), nausea or vomiting. This may be caused by:
  
  
• • Kidney disease
    
    
  • Liver disease
    
    
  • Diabetes mellitus
    
    
  • Shock
    
    
  • Drug intoxication
    
    
  • Poisoning or overdose from aspirin, antifreeze or wood alcohol
    
    
• Metabolic alkalosis. A high pH combined with high HCO3 and PaCO2 is an indicator of metabolic alkalosis. Symptoms include slow and shallow breathing (hypoventilation), restlessness, twitching, extremely tense muscles, confusion, irritability, seizures, lack of emotion (apathy), muscle spasms and prolonged unconsciousness (coma). This may be caused by:
  
  
• • Primary aldosteronism (or Conn’s disease). An endocrine disorder in which overproduction of the hormone aldosterone causes the kidneys to absorb too much sodium and water and eliminate too much potassium.
    
    
  • Cushing syndrome. An endocrine disorder in which the adrenal glands produce an excess of cortisone-like hormones.
    
    
  • Steroid overdose.
    
    
  • Loss of potassium.
    
    
  • Improper diet resulting in too much alkali ingestion.
    
    
  • Prolonged vomiting.

ABG results can be used to diagnose a variety of other conditions as well, which is why these tests are so widely used in emergency departments of hospitals.