[Erythrocyte volume and 2,3-DPG level. A study on a primary polycythemia model]

Recent studies from this department have suggested that the level of 2,3-DPG may be determined in part by the volume of the erythrocyte; this conclusion was reached on the basis of the finding of significantly elevated values of 2,3-DPG in heterozygous beta-thalassemia, even in the absence of anemia. In order to test the role of microcytosis in the formation of 2,3-DPG levels, a study was undertaken on a different patient material characterized by microcytosis without anemia or hypoxia, namely on cases of polycythemia vera (PV) rendered microcytic through therapeutic venesection (or blood loss) and on appropriate controls. Five cases of untreated PV (mean HB 18.36 +/- 1.53 g/dl, mean MCV 94.4 +/- 3.9 fl) had 2,3-DPG levels slightly lower than normal controls (13.67 +/- 0,75 mumoles/g Hb vs 14.18 +/- 1.41 mumoles/g Hb). Six microcytic iron deficient PV's (mean Hb 17.42 +/- 2.34 g/dl, mean MCV 74.5 +/- 6.2 fl) had very significantly increased 2,3-DPG levels (17.73 +/- 1.75 mumoles/g Hb). Similar high levels were obtained in five cases venesected in the past and maintained with cytostasis (mean Hb 15.22 +/- 0.67 g/dl, MCV 82.5 +/- 7.5 fl, 2,3-DPG 17.04 +/- 2.44 mumoles/g Hb). A strong linear negative correlation was obtained between 2,3-DPG values and the MCV (r = -0.736, P less than 0.001). It is concluded that microcytosis of other etiology and not only of beta-thalassemia may also lead, per se, to increased levels of 2,3-DPG. The different levels of 2,3-DPG in PV undergoing venesection vs untreated patients may explain some discrepant reports on the behavior of this metabolite in PV.