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Pulmonary vascular gas transfer pattern — SCE Respiratory MCQ

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HardRespiratory PhysiologyPulmonary vascular gas transfer patternSCE Respiratory

A patient with exertional dyspnoea has normal spirometry and HRCT. Uncorrected TLCO is 54% predicted, KCO 59% predicted and haemoglobin 82 g/L because of iron deficiency. What is the most defensible next interpretation step?

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Correct answer: B — Correct or report TLCO for the measured haemoglobin before assigning a gas-transfer lesion

Explanation lettering: D = shown as A · A = shown as C · C = shown as D

B is correct. Carbon-monoxide transfer depends on haemoglobin available to bind test gas, so substantial anaemia lowers measured TLCO and KCO even without intrinsic parenchymal or vascular disease. The current haemoglobin should be incorporated into the correction or clearly reported before a low value is attributed to pulmonary pathology. Low KCO is not specific for emphysema, TLCO does not diagnose restriction without lung volumes, and alveolar volume cannot remove the effect of severe anaemia.

Reference: https://pmc.ncbi.nlm.nih.gov/articles/PMC7337892/