Determination of the transfer factor provides useful non- specific information regarding the gas-transfer function of the lungs.
To perform the test the patient:
- exhales completely
- then maximally inhales air with a trace quantity of carbon monoxide
- then holds their breath for ten seconds
The transfer factor is the quantity carbon monoxide transported across the alveolar-capillary membrane in each minute per unit of pressure gradient.
There are several variables which can influence the value of the transfer factor recorded, including:
- an impairment of ventilation / perfusion
- alveolar-capillary membrane thickness
- area of the alveolar capillary membrane
- blood volume in the pulmonary capillaries
- concentration of haemoglobin
- the rate of reaction of haemoglobin with CO
Last reviewed 01/2018