Carbon monoxide diffusing capacity in polycythaemia rubra vera.

The diffusing capacity of the lung, or transfer factor, for carbon monoxide (TLCO) was measured in 12 patients with polycythaemia rubra vera. This was significantly raised (mean 152% predicted, SEM +/- 14%) and remained so even after correction to a standard haemoglobin concentration of 14 . 6 g/dl (mean 139% predicted, SEM +/- 13%). Serial measurements of TLCO on two patients after treatment of polycythaemia rubra vera showed a greater fall in relation to haemoglobin concentration than would have been predicted on theoretical grounds if the increases in TLCO had been due entirely to the increased haemoglobin concentration. The pulmonary capillary blood volume (estimated from TLCO) also fell in these two patients after treatment. There was a strong correlation between TLCO and the technetium-99m-labelled red cell volume for the seven men (r = 0 . 92; p less than 0 . 01) and five women (r = 0 . 99; p less than 0 . 001) when studies were performed on the same day. In patients with polycythaemia rubra vera who have no evidence of coexistent pulmonary disease the pulmonary capillary bed appears to share in the expansion of the body blood volume. The single-breath TLCO test may act as a convenient and simple monitor for the response of the disease to treatment.