Effect of time and storage on toxic or pseudo-toxic change in canine neutrophils

Background The presence of toxic change in neutrophils is frequently used as a biomarker of inflammation in dogs. Objective We aimed to evaluate the effect of time and storage on toxic change in canine neutrophils. Methods One hundred and fifty microliters of EDTA blood were obtained from eight dogs with no toxic neutrophil changes observed on fresh blood smears (T0). Blood was stored at room temperature (RT), in a box with an icepack (ICE), and at 4 degrees C. For each storage condition, smears were prepared 2 (T2), 4 (T4), 8 (T8), and 24 (T24) hours post blood draw. Smears were randomized, and each smear was evaluated for the presence of toxic neutrophil change. Results A statistically significant effect of time and storage on the presence of toxic neutrophil change was observed. Compared with T0, the number of neutrophils containing Dohle bodies was significantly higher at T8 and T24 for the RT (P < 0.0001) and ICE (P < 0.0001) samples and at T24 for 4 degrees C samples (P < 0.0001). Additionally, smears were falsely classified as having 1+ toxic change in 0/8 (T2), 1/8 (T4), 3/8 (T8), and 8/8 (T24) for RT samples; 0/8 (T2 and T4), 2/8 (T8), and 5/7 (T24) smears for ICE samples; and 0/8 (T2, T4, and T8) and 2/8 (T24) for 4 degrees C samples. Conclusions Smears can be falsely classified as having neutrophils with toxic change as early as 4 hours post blood draw in samples stored at RT, 8 hours when stored with icepacks, and 24 hours when stored at 4 degrees C. Canine blood smears should be prepared and evaluated for toxic neutrophil change as early as possible.