Respiratory acidosis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Vamsikrishna Gunnam M.B.B.S [2]

Overview

Laboratory findings consistent with the diagnosis of respiratory acidosis include arterial blood gas (ABG), complete blood count(CBC), toxicology screen, thyroid function tests, creatine phosphokinase 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 a vital routine investigation to monitor the acid-base balance of patients with respiratory acidosis.
• Henderson-Hasselbalch equation: Used for the bicarbonate level calculation in the blood gas analysis.
• On ABG analysis pH (< 7.35)  is considered as academia.
• When increased the partial pressure of arterial carbon dioxide (PaCO₂) (>45 mm Hg) it is considered as acidemia of respiratory origin.
• Hypoxemia that causes 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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