Prescribed DLCO: what does this lung transfer test measure?

New breathlessness without respiratory distress needs medical assessment the same day. In France, call 15 or 112 immediately if it prevents you from finishing sentences or comes with bluish lips or changes in alertness. A planned DLCO measurement must not delay this assessment.

DLCO means the diffusing capacity of the lung for carbon monoxide. It examines gas transfer across the membrane separating the lung's air sacs from their small blood vessels. It complements the volumes and airflow measured by spirometry, which describe the air moved during breathing.

The test uses a diagnostic gas mixture containing a very low concentration of carbon monoxide and a tracer gas. In the method described by HAS, you breathe out, inhale the mixture, briefly hold your breath and then exhale into the device in a controlled way. Trained staff guide these manoeuvres; ask them to explain the instructions before starting.

The device analyses inhaled and exhaled gases to estimate lung transfer. The result is compared with reference values. This differs from arterial blood gas analysis, which measures gases in a blood sample. Ask which parts of your assessment examine airflow, gas transfer or oxygenation of the blood.

DLCO is interpreted alongside symptoms and other findings, including imaging. For idiopathic pulmonary fibrosis, the French national care protocol describes a reduced DLCO that may be the only functional abnormality and notes that normal lung function tests remain possible. A single value is therefore insufficient to identify or exclude a disease yourself.

For a test already prescribed, clarify which additional information is being sought after your previous examinations and which instructions apply to the appointment. Ask how the manoeuvres' quality will be checked and who will relate the result to the rest of your assessment. The report supports that discussion; the name DLCO alone does not identify the doctor's diagnosis.