Artifactual changes in Sprague-Dawley rat hematologic parameters after storage of samples at 3 °C and 21 °C.

Circumstances can occur that prevent timely analysis of blood samples. The purpose of this study was to characterize artifactual changes in rat hematologic parameters after storage of samples at 3 and 21 °C and to document the effects of storage on peripheral blood smear findings. EDTA-treated blood samples were collected from 12 male Sprague–Dawley rats. Samples were analyzed on an impedance hematology analyzer within 5 min after collection and then at 6, 24, 48, and 72 h after storage at 3 °C or 21 °C. Corresponding blood smears were examined microscopically. RBC count and hemoglobin concentration had not changed after 72 h at either temperature. At 3 °C, the instrument-derived hematocrit and manually measured PCV remained unchanged for 72 h. Compared with 0-h values, platelet counts and MCV at 6 h and MPV at 24 h were higher at either temperature. In general, WBC count and neutrophil and lymphocyte percentages were unchanged for at least 48 h at either temperature. Prominent blood smear findings were smudge cells, pyknotic leukocytes, echinocytes, and spheroechinocytes. Although some observed changes were within analytic variability or clinically negligible, the best practice likely is to measure hematologic parameters within 6 h after collection. In the event of delayed analysis, specimens should be stored in the refrigerator, and care must be taken not to misinterpret artifactual changes as pathologic findings.