Respiratory acidosis laboratory findings

Overview

• Laboratory findings consistent with the diagnosis of respiratory acidosis include Arterial blood gas (ABG) which are helpful in the diagnosis of respiratory acidosis.

Laboratory Tests

Arterial blood gas (ABG)

• An elevated/reduced concentration in Arterial blood gas (ABG) is diagnostic of respiratory acidosis.

• Arterial blood gas analysis is vital routine investigation to monitor the acid-base balance of patients with respiratory acidosis.
• Henderson-Hasselbalch equation: Used for the bicarbonate level caluculation in the blood gas analysis.
• On ABG analysis pH (< 7.35)  is considered as aacidemia.
• When increased partial pressure of arterial carbon dioxide (PaCO₂) (>45 mm Hg) it is considered as acidemia of respiratory origin.
• Hypoxemia  that cause respiratory acidosis is frequently associated with pulmonary diseases.
• Bicarbonate levels are one of the most common abnormal serum electrolyte finding on ABG analysis, Although this feature is nonspecific as other etiologies.

Complete blood count(CBC)

• Some patients with respiratory acidosis may have polycythemia due to Chronic hypoxemia from underlying lung disease.
• Eosinophilic myalgia: Although this condition is rare, An elevated eosinophil count on CBC may be consistent with eosinophilic myalgia.

Toxicology screen

• Screening for specific drugs should be performed that includes
  • Opiates
  • Benzodiazepines
  • Tricyclic antidepressants
  • Barbiturates

Thyroid function tests

• Some patients with respiratory acidosis may have elevated concentration of thyroid stimulating hormone (TSH) and low thyroxine (T4) , which is usually suggestive of hypothyroidism.

Creatine phosphokinase

• An elevated concentration of creatine phosphokinase (CPK) is diagnostic of infectious or autoimmune polymyositis rhabdomyolysis which is secondary to colchicine or chloroquine toxicity, or procainamidemyopathy.

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