From the Guidelines
Isolated reduced diffusing capacity of the lungs for carbon monoxide (DLCO) can be caused by several conditions, including pulmonary vascular diseases, anemia, early interstitial lung diseases, emphysema, certain medications, heart failure, pulmonary hemorrhage syndromes, and recent lung surgery or radiation therapy. The most common causes of isolated reduced DLCO include:
- Pulmonary vascular diseases such as pulmonary embolism, pulmonary hypertension, and pulmonary vasculitis, which reduce the available surface area for gas exchange 1
- Anemia, which decreases the hemoglobin available to bind with carbon monoxide during the test 1
- Early interstitial lung diseases, particularly those affecting the alveolar-capillary membrane like hypersensitivity pneumonitis or early pulmonary fibrosis, which can reduce DLCO before affecting lung volumes 1
- Emphysema that predominantly affects the lower lobes, which may present with isolated DLCO reduction 1
- Certain medications like amiodarone, bleomycin, and nitrofurantoin, which can cause drug-induced lung injury that primarily affects diffusion capacity 1
- Heart failure, particularly left-sided heart failure, which can cause pulmonary congestion that impairs gas transfer 1
- Pulmonary hemorrhage syndromes and recent lung surgery or radiation therapy, which may also result in isolated DLCO reduction 1 When encountering reduced DLCO with normal lung volumes, clinicians should consider these possibilities and pursue appropriate diagnostic testing based on the patient's clinical presentation and risk factors 1. It is essential to note that a decrease in DLCO can be associated with a poor outcome, especially if it is severely reduced, defined as <45% of predicted 1. Therefore, it is crucial to investigate the underlying cause of isolated reduced DLCO and manage it accordingly to improve morbidity, mortality, and quality of life.
From the Research
Causes of Isolated Reduced DLCO
- Isolated reduced DLCO can be caused by various factors, including systemic sclerosis (SSc) without cardio-pulmonary involvement at baseline 2
- In patients with SSc, isolated reduced DLCO may be associated with the presence of anticentromere autoantibodies and may precede the development of pulmonary arterial hypertension (PAH) 2
- Exercise pulmonary hypertension can also cause isolated reduced DLCO, particularly in patients with parenchymal lung disease 3
- In some cases, isolated reduced DLCO may not be clinically significant and may not necessitate additional medical inquiry, as seen in healthy, asymptomatic, young women 4
- Determinants of impairment in lung diffusing capacity in patients with systemic sclerosis include interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH), which can affect alveolar-capillary membrane conductance (Dm) and pulmonary capillary blood volume (Vc) 5
- Low DLCO can also be observed in idiopathic pulmonary arterial hypertension (IPAH) patients, and is associated with worse functional status, exercise capacity, and higher prevalence of coronary artery disease, as well as increased risk of death 6