IN-VITRO CULTURE-GROWTH OF ERYTHROID PROGENITORS AND SERUM ERYTHROPOIETIN ASSAY IN THE DIFFERENTIAL-DIAGNOSIS OF POLYCYTHEMIA

Background We assessed the in vitro culture growth of erythroid progen itors [burst forming unit-erythroid (BFU-E)] and serum erythropoietin (EPO) levels in different groups of polycythaemia to determine the dis criminative power in the differential diagnosis of polycythaemia. Meth ods We used the methylcellulose culture technique to study the growth of endogenous erythroid colonies (EECs) and EPO-dependent BFU-E from b one marrow (BM) and/or peripheral blood (PB) cells from 40 patients wi th polycythaemia vera (PV), 13 with secondary polycythaemia (SP), 19 w ith pure erythrocytosis (PE), five with PE and PV evolution later (PE- PV), and 12 with relative polycythaemia (RP). The serum EPO levels wer e measured by radioimmunoassay before treatment in 47 PV patients, 23 SP patients, 19 PE patients, five PE-PV patients and 16 RP patients, a s well as after treatment in 38 PV patients, five PE-PV patients and 1 2 PE patients. Results The results of the erythroid progenitor culture assay showed that the numbers of EPO-dependent BFU-E in BM did not di ffer significantly among groups. The PB BFU-E were significantly highe r in PV than in SP or PE, and no statistical differences were found am ong patients with SP, PE and RP. There was a correlation between BM BF U-E and PB BFU-E in the individual PV and PE patients. EECs were prese nt in all EM and PB cultures of untreated and phlebotomy-treated PV an d PE-PV patients, but were absent in 6 of 17 PV patients who had recei ved cytotoxic therapy. EECs were not found in SP, PE and RP. PB could substitute for BM in the EEC or the BFU-E assay. Both pretreatment and posttreatment serum EPO levels of PV and PE-PV were similar, which we re significantly lower than SP, PE or RP. The serum EPO levels in trea ted PV or PE-PV patients who had normal haematocrit values were not si gnificantly different from those in untreated patients. In contrast, t he phlebotomy-treated PE patients had significantly higher serum EPO v alues than untreated PE patients. In the differentiation between PV an d PE, the sensitivity, specificity, positive predictive value and nega tive predictive value of post-treatment serum EPO levels at a cut-off level of less than or equal to 9 U L-1 were 74%, 92%, 97% and 52% resp ectively. The discriminative power of post-phlebotomy serum EPO levels was even higher with a positive predictive value of 80% and negative predictive value of 92% for the prediction of PV evolution in patients with pure erythrocytosis of unknown origin. Conclusion The present st udy showed that apart from EEC assay, the post-phlebotomy serum EPO le vel was a sensitive and specific parameter in the differential diagnos is of polycythaemia, in particular for the identification of PV among patients with unclassifiable polycythaemia.