Concerning the PVSG cohort of PV patients 25% showed a slight and 11% a moderate to marked increase in reticulin.68, 79 An increase in reticulin in PV has been associated with worse clinical outcome associated with a more rapid progression to post-PV myelofibrosis.78 For this reason, a BM biopsy may even be recommended in cases presenting with sustained absolute erythrocytosis (Hb levels>18.5 g/dl in men—Hct 55.5% or >16.5% g/dl in women—Hct 49.5%) together with all the other criteria (Table 1). Here, GSTM1 is linked to acquired polycythemia vera.