ATS GUIDELINES Bundle

Routine Lung Function Tests

American Thoracic Society Quick-Reference GUIDELINES Apps

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11 Diffusing capacity of the lungs for CO (D L CO) • Increased blood flow   ▶ e.g., left-to-right shunt, asthma, obesity • Alveolar hemorrhage • Erythrocytosis • Pulmonary vascular abnormality   ▶ e.g., pulmonary hypertension, pulmonary embolism, vasculitis • Emphysema with preserved lung volume • Anemia >ULN (95th percentile) Abnormally high Normal First determine if the D L CO is low or high based on the lower and upper bounds defined by the 5th and 95th percentiles of the reference values. A high D L CO is almost always due to increased pulmonary blood volume, as in a le to right shunt, increased hemoglobin, as in erythrocytosis, or free hemoglobin in any component of the airway, as in alveolar hemorrhage. To further understand the cause of a low D L CO, next examine its components, V A and K CO . If V A is normal then this is consistent with pulmonary vascular abnormalities, emphysema with preserved lung volume, or anemia. If V A is low and K CO is low or normal, then there is typically loss of alveolar capillary structure, such as in ILD, or emphysema with loss of lung volume. If V A is low and K CO is high, then there is a low lung volume state, either due to localized loss of lung volume, such as from lung resection, which may raise K CO somewhat, or incomplete lung expansion, such as failure to fully inspire, which can increase K CO substantially.

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