Evaluation of peroxidase activity by alpha-naphthol/pyronine staining compared with benzidine staining in 101 acute leukemia cases

Quick staining technique for myeloperoxidase using potassium iodide and oxidized pyronine B

Myeloperoxidase (MPO) staining has been important for the cytomorphological diagnosis and classification of leukemia. A novel staining method for MPO and its clinical application are presented in the report. Pyronine B (PyB), serving as a chromogenic reagent, was pre-oxidized to obtain stable oxidized Pyronine B solution. The MPO working solution for oxidized pyronine B method consisted of phosphate buffer solution, potassium iodide (KI) solution, and oxidized Pyronine B solution. The positive products of the oxidized Pyronine B method of MPO staining were vibrant red particles located in cytoplasm and the nucleus was stained bluish green. Bone marrow smears from 229 patients with acute leukemia or with grossly normal bone marrow were stained by both oxidized Pyronine B method and the conventional Washburn benzidine staining and a comparison revealed no significant difference in the positive detection rate between the two techniques. The new method eliminates the influence of the varying amount of H₂O₂ on MPO staining. With this method, the reagents were more stable and the staining procedure was simple and time-saving. This MPO staining technique is a better alternative than the conventional benzidine-based methods.

Positive rate and score discrepancies of myeloperoxidase staining at different temperatures

Myeloperoxidase (MPO) is a strong marker of acute myeloid leukemia. The aim of this study was to compare MPO staining at different temperatures. Four bone marrow aspirate smears of each case were incubated with MPO staining solution at 4°C, 20°C, 37°C and 50°C, respectively. 30 patients with score <150 at 50°C were group A; 26 patients with score ≥150 at 50°C were group B. The results showed that at 4°C, MPO-positive blasts in two cases of group A were both 2%; at 50°C, MPO-positive blasts in the two cases were 42% and 30%, respectively. At 4°C, 20°C, 37°C and 50°C, the mean positive rates of group A were 30.6%, 42.2%, 53.7% and 56.5%, respectively (P<0.001); their mean scores were 52.2, 75.9, 99.5 and 105.3, respectively (P<0.001); the mean positive rates of group B were 84.1%, 88.7%, 92.3% and 93.7%, respectively (P<0.001); their mean scores were 199.5, 224.7, 243.5 and 244.5, respectively (P<0.001). From this study we can conclude that most MPO staining is effective over a wide temperature range with the highest positive rate at 50°C. MPO staining intensity at low temperature is much lower and may be false negative. Good MPO staining is achieved at 37°C.