Measurement of endogenous plasma thrombopoietin in patients with acquired aplastic anaemia by a sensitive enzyme‐linked immunosorbent assay

We measured the endogenous plasma concentration of thrombopoietin (TPO) in 76 patients with acquired aplastic anaemia (AA) by a sensitive sandwich enzyme-linked immunosorbent assay (ELISA). The plasma TPO concentrations were significantly higher in AA patients when compared to healthy control subjects (P < 0.0001) and there was a significant negative correlation between plasma TPO concentrations and platelet counts in 54 AA patients who had not received any platelet transfusions prior to sampling. On the other hand, there was no statistically significant correlation between the TPO concentrations and platelet counts in 22 AA patients who had previously received platelet transfusions. We studied serial changes of plasma TPO concentration in 24 patients who showed an increase in their platelet counts following bone marrow transplantation or immunosuppressive (IS) therapy. Although a decrease in plasma TPO concentration was observed, levels remained above the range of normal healthy controls even in the patients who attained normal platelet counts following therapy. A decrease in TPO concentrations was observed in only half of the responders to IS therapy. Whether exogenous TPO will result in increased platelet counts in AA patients with high TPO levels remains to be determined.