Plasma levels of immunoreactive erythropoietin after acute blood loss in man.

Plasma levels of immunoreactive erythropoietin (Ep) were measured after acute blood loss (50, 75, 200 and 450 ml) in man in order to determine the volume of blood loss required to trigger an Ep response as well as to define the reticulocyte response. There was a highly significant (P less than 0.01) linear increase in reticulocyte count after 200 and 450 ml of blood loss. Analysis of trends also showed a highly significant (P less than 0.01) linear response of haematocrit and Ep after a 450 ml blood loss. The reticulocyte count increases were not dependent on a prior increase in Ep level indicating that at least two mechanisms are operative in restoring the red cell mass to normal after blood loss.