Last reviewed 01/2018

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