Basics | transfer factor


Besides ventilation, the diffusion of respiratory gases represents an important element in the assessment of pulmonary function. This is made possible in everyday clinical practice through the measurement of uptake of carbon monoxide (CO) into the blood. This is referred to as transfer factor.

The ventilation-dependent determination of the alveolar volume (VA) by using helium can be defined in relation to TLCO and is then referred to as transfer coefficient or Krogh index (TLCO/VA). In combination with the TLCO, it allows the differentiation between genuine diffusion and distribution disturbances: with diffusion disturbances, the TLCO is reduced to the same extent as Krogh index, as can be recognized by the deviation in percentage from the normal value (Drop in TLCO = drop in TLCO/VA). With distribution disturbances, the TLCO drops much more steeply than the Krogh index (Drop in TLCO >> drop in TLCO/VA).

The following factors contribute to a decrease in TLCO:

  • reduced alveolar volume
  • reduced pulmonary blood flow
  • COPD/emphysema, cardiac insufficiency, pulmonary edema, anemia, pulmonary embolism, pulmonary hypertension, illnesses affecting lung tissue and airway geometry, pneumonia, muscle illnesses, lung resection, sarcoidosis
  • smoking (HbCO)

The following factors contribute to an increase in TLCO….

  • increased pulmonary blood flow
  • hemoptysis (reason: hemoglobin, which may be found in the bronchial lumen in the form of bleeding/hemorrhage, also binds to CO and thus affects TLCO)
  • asthma bronchiale, polyglobulia, illnesses associated with left-right shunt

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Diagnostics and follow-up of pulmonary diseases, evaluation of preoperative risk as well as toxicity of cytostatic agents. There are no relevant contraindications for the determination of transfer factor.

Normal findings and normal values

The following division is frequently employed in clinical practice for the assessment of a reduction of transfer factor:

transfer factor classification

Original findings

diffusion disorder

67-year-old female patient with extremely severe obstruction as shown by body plethysmography (FEV1=25% of the target value) with no broncholytic success and severe, non-reversible emphysema.

Findings severe diffusion disturbance with transfer factor reduced to 33.4% of the target value (DLCO SB). At the same time, a decrease in the transfer coefficient (DLCO/VA) is observed.

distribution disorder

72-year-old male patient with moderate restriction (VC 55.2% of the target value, TLC 74.5%)

Findings transfer factor reduced to 66.2% of the target value with normal value transfer coefficient of 103.3%, as would be expected for a severe distribution disorder.