transfer factor
Transfer factor is simply another name for DLCO, more common in British and European usage. The two terms describe exactly the same measurement: how efficiently a test gas crosses from the air spaces into the blood with each breath.
Some clinicians prefer transfer factor because it sidesteps the slightly misleading word capacity — the test does not measure a maximum reservoir but rather a rate of transfer per unit of driving pressure. When you see TLCO on a European report, read it as the identical concept to DLCO.
The two limbs of transfer are sometimes separated into the membrane component (how easily gas crosses the wall) and the blood component (how much haemoglobin is available to soak it up). Splitting them can pinpoint whether a low value comes from a thickened membrane or from reduced capillary blood volume.
A European report lists TLCO at 5.2 mmol/min/kPa, 58 percent of predicted — the same finding a North American report would label as a reduced DLCO.
Transfer factor and DLCO are two names for one measurement.
TLCO is the same as DLCO; KCO (the transfer coefficient) is TLCO divided by the alveolar volume, helping distinguish small lungs from intrinsically poor transfer.