Chronic bronchitis laboratory findings

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

Chronic bronchitis has irreversible airflow limitation, especially during forced expiration. This is due to the destruction of lung tissue and increase in resistance to flow in the conducting airways. Thus, it doesn’t show an improvement in FEV1 post bronchodilator administration, unlike asthma. This characteristic feature is used as an diagnostic criterion for COPD, i.e. a COPD is diagnosed by spirometry if FEV1/FVC < 70% for a matched control.^[1] Arterial blood gas may show hypoxemia with or without hypercapnia depending on the disease severity. pH may be normal due to renal compensation. A pH less than 7.3 usually indicates severe respiratory compromise. A blood sample taken from an artery, i.e. Arterial Blood Gas (ABG), can be tested for blood gas levels which may show low oxygen (hypoxemia) and/or high carbon dioxide (respiratory acidosis if pH is also decreased). A blood sample taken from a vein may show a high blood count (reactive polycythemia), a reaction to long-term hypoxemia.

• Pulse oximetry is not as accurate in predicting the percentage oxygen saturation as arterial blood gas analysis, but it provides a quick estimate of patient status when combined with the clinical status.

• ABG may show changes of hypoxemia and hypercapnia depending on the severity of disease.
• Milder exacerbation may present only with hypoxemia without accompanied hypercapnia.
• Hypercapnia is usually seen when FEV1 falls below 1 L/s or 30% of the predicted value.
• A pH value below 7.3 usually indicates a severe exacerbation and respiratory compromise.

• COPD patients may have hypoxemia due to the chronic underlying disease. This chronic hypoxemia may lead to polycythemia (hematocrit > 52% in men or 47% in women is diagnostic of polycythemia).
• Correction of hypoxemia should reduce secondary polycythemia in patients who have quit smoking.

• A blood test would indicate inflammation as indicated by a raised white blood cell count and elevated C-reactive protein.
  • Neutrophils infiltrate the lung tissue, aided by damage to the airways caused by irritation.
  • Damage caused by irritation of the airways leads to inflammation, leading to neutrophil infiltration.
  • Mucosal hypersecretion is promoted by a substance released by neutrophils
  • Further obstruction to the airways is caused by more goblet cells in the small airways which is typical for chronic bronchitis.
  • Although infection is not the reason or cause of chronic bronchitis, it is seen to aid in sustaining the bronchitis.

• COPD patients have irreversible obstruction of airways that causes retention of carbon dioxide. This in turn causes them to develop chronic respiratory acidosis. To compensate for this, the body may develop metabolic alkalosis that leads to increased bicarbonate production. Bicarbonate levels act as useful indicator of disease progression.

• Research is ongoing on Human B-type natriuretic peptide (BNP) and pro-BNP to determine if it can help to differentiate between congestive heart failure and COPD.

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