Chronic obstructive pulmonary disease laboratory findings
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Chronic obstructive pulmonary disease Microchapters |
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Differentiating Chronic obstructive pulmonary disease from other Diseases |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Philip Marcus, M.D., M.P.H. [2]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [3]
Overview
Chronic obstructive pulmonary disease has irreversible airflow limitation specially 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 criteria for COPD, i.e. a COPD is diagnosed by spirometry if FEV1/FVC < 70% for a matched control. 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 indicate severe respiratory compromise.
Laboratory Tests
Arterial blood gas (ABG)
- 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.
Serum electrolytes
COPD patients have irreversible obstruction of airway 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.
Spirometry
COPD is particularly characterized if a ratio of forced expiratory volume over 1 second (FEV1) to forced vital capacity (FVC) being < 0.7 and the FEV1 < 70% of the predicted value when compared with a matched control. [1], [2] (see Spirometry).
The severity of COPD can be classified as follows using spirometry (see above):
| Severity | FEV1 /FVC | FEV1 % predicted |
|---|---|---|
| At risk | >0.7 | ≥80 |
| Mild COPD | ≤0.7 | ≥80 |
| Moderate COPD | ≤0.7 | 50-80 |
| Severe COPD | ≤0.7 | 30-50 |
| Very Severe COPD | ≤0.7 | <30 or 30-50 with Chronic Respiratory Failure symptoms |
Sputum culture
Though sputum culture can be done and yields organisms like Streptococcus pneumonia, and Hemophilus influenza during acute exacerbation, they are not otherwise useful in management plans.
Human B-type natriuretic peptide
- Research are ongoing on Human B-type natriuretic peptide (BNP) and pro-BNP to find if it can help to differentiate between congestive heart failure and COPD. However, no conclusive results are still drawn.