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.