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TLCO Reduced Emphysema — FRCA Primary MCQ

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HardPhysiology - RespiratoryTLCO Reduced EmphysemaFRCA Primary

Which change most reliably lowers the carbon-monoxide transfer factor (TLCO) by reducing alveolar-capillary surface area?

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Correct answer: B — Emphysema destroying alveolar walls and pulmonary capillary bed

The best answer is “Emphysema destroying alveolar walls and pulmonary capillary bed”. Emphysema lowers TLCO because destruction of alveolar septa reduces both available diffusion surface and pulmonary capillary bed. Polycythaemia, exercise, pulmonary haemorrhage and increased pulmonary blood volume tend to increase measured carbon-monoxide uptake. Anaemia, fibrosis and pulmonary vascular obstruction are other important causes of a reduced result.

Reference: Royal College of Anaesthetists, Primary FRCA Syllabus 2021: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf