blood and bone marrow in polycythaemia . Erythroid colony growth from peripheral

Erythroid colony growth in the presence and absence of erythropoietin was compared in 23 patients with primary proliferative polycythaemia (PPP), nine with idiopathic erythrocytosis, 10 with secondary polycythaemia, 15 with pseudopolycythaemia and in 76 normal subjects. Erythroid colonies growing without erythropoietin stimulation (endogenous erythroid colonies) from peripheral blood (BFU-E) were found in 20 of 22 patients with PPP and in two of seven with idiopathic erythrocytosis. None was found in secondary polycythaemia, pseudopolycythaemia, or in normal subjects. Small numbers of endogenous colony forming units-erythroid (CFU-E) (though not BFU-E) were cultured from the bone marrow of three of 24 normal subjects, suggesting that peripheral blood cultures provide a more specific indicator of clonal erythropoiesis. Peripheral blood endogenous erythroid colony growth is an effective and convenient means of distinguishing patients with clonal erythrocytosis and may be of particular value when iron deficiency obscures the diagnosis of PPP on conventional criteria. Department of Haematology,. University Hospital of Wales, Heath Park, Cardiff CF4 4XW G S Masters P Baines A Jacobs Correspondence to: Miss G S Masters Accepted for publication 6 July 1990 True erythrocytosis may be the result of increased concentrations of erythropoietin, caused-for example, by hypoxia or a renal carcinoma (secondary polycythaemia)-or it may be due to the clonal expansion of an abnormal haemopoietic stem cell which can also result in an increase in the numbers of leucocytes and platelets (primary proliferative polycythaemia) (PPP). Patients who do not meet the standard criteria for PPP' and who do not have a demonstrable cause for their erythrocytosis are grouped together as having idiopathic erythrocytosis. This is a heterogeneous group, some of whom may be in the early stages of PPP, and who go on to develop all the features of this disease. In 1974 Prchal et al reported that cultured marrow erythroid progenitors from patients with PPP formed colonies in vitro without the addition of erythropoietin-endogenous erythroid colonies (EEC).2 EEC were shown to be produced by the abnormal clone3 and have been found in other myeloproliferative disorders.45 As well as being used to distinguish PPP from secondary polycythaemia, particularly in cases where the standard criteria are not satisfied,6 EEC have recently been used to identify a subgroup of patients with idiopathic erythrocytosis who have clonal disease and who may therefore be at greater risk of developing ppp.7 8 We compared peripheral blood with bone marrow cultures to detect EEC growth, because peripheral blood is more easily obtained. These studies were carried out in patients with true erythrocytosis (PPP, idiopathic erythrocytosis, secondary polycythaemia), those whose increased haematocrit was due to reduced plasma volume (pseudopolycythaemia),9 and in normal subjects to identify the different patterns of growth in clonal and non-clonal erythropoiesis. We also report the finding of EEC in four patients with iron deficiency who did not meet the criteria for PPP. Methods The clinical details of the patients and normal subjects included in this study are summarised in table 1. Most patients were studied at presentation and none had received any treatment other than venesection before testing. PRIMARY PROLIFERATIVE POLYCYTHAEMIA The criteria for this diagnosis were based on those suggested by the Polycythaemia Study Table 1 Summary of clinical details ofpatients and normal controls