Megakaryocyte ploidy in thrombocytosis: improved microdensitometric measurements with a new image analysis system

Megakaryocyte (MK) nuclear deoxyribonucleic acid (DNA) content was measured on a new image analysis system. Feulgen-stained bone marrow aspirate smears were analysed from 9 patients with thrombocytosis. Average optical density (OD) of stained nuclei was evaluated by pixel discrimination over 128 grey levels. Projected nuclear area was delineated manually. The product of these two parameters gave an index of nuclear DNA content. Neutrophils were used as 2N reference cells. Reproducibility of OD, nuclear area and their product was excellent for individual cells (CV less than 2.0% for MKs, less than 4.0% for neutrophils). The average CV for DNA content of 18 groups of 10 neutrophils was 5.5% (range 3.0-9.7%). A significant linear regression existed between MK nuclear area and DNA content (p much less than 0.001) for 627 MKs in essential thrombocythaemia (ET) and 346 MKs in reactive thrombocytosis (RT). Compared with RT, more 8N and 64N MKs were seen in ET (p less than 0.05). 128N MKs were unique to ET. Image analysis of MK ploidy may assist the clinical discrimination between primary and secondary thrombocytosis.