The relationship between the transfer factor obtained at rest, and arterial oxygen tension during exercise, in...

Forty-one consecutive patients with the symptom 'exertional dyspnoea' were referred to the Department of Clinical Physiology for evaluation. Pulmonary fibrosis and chronic obstructive pulmonary disease were the most common diagnoses but other diagnoses were also represented. Some patients had no clinical diagnosis or radiological signs. All patients underwent exercise testing with sampling of arterial blood for blood gas analysis and pulmonary function testing including measurement of the transfer factor (carbon monoxide diffusing capacity) at rest. Independent of spirometric findings and diagnosis a significant correlation (r = 0.80, P < 0.001) was shown to exist between the transfer factor measured at rest and the arterial oxygen tension at maximal exercise level. We recommend measurement of the transfer factor as a screening test for exertional hypoxaemia and suggest that exercise blood gas analysis only seems necessary in patients with a transfer factor between 55% and 80% of the predicted value.