A reliable method with good cell preservation for the demonstration of peroxidase activity in human platelets and megakaryocytes.

We have tried to improve existing methods for demonstration of platelet peroxidase (PPO) in human platelets and megakaryocytes by introducing a fixation of 0.1% glutaraldehyde prior to incubation in the DAB medium. This prefixation with low concentration of glutaraldehyde preserves excellent morphological detail and does not inhibit PPO activity. All 23 platelet-rich plasma samples show PPO reaction product in the dense tubular system after incubation in DAB medium with 0.003% H2O2. When 0.01% H2O2 is used in excessive DAB medium, PPO activity can also be demonstrated in platelets and megakaryocytes of bone-marrow cell suspensions. This method can be used for the identification of megakaryoblasts in acute non-lymphocytic leukemia, myelodysplastic syndromes and in blastic crisis of chronic myeloid leukemia. PPO cytochemistry can be combined with postfixation in a OsO4-ruthenium red mixture. This method reveals alpha-granules, dense bodies, microtubuli, glycogen, mitochondria, dense tubular system and invaginated membrane system in the same platelet and is useful for investigation of platelet ultrastructure.