Effects of sample storage time and temperature on equine complete blood counts

Abstract

Routine veterinary care often involves complete blood counts (CBC) to monitor equine health. Blood samples are often collected in unregulated, distant environments and must be stored for later analysis. While impacts of storage methods on CBC parameters have been studied in humans, there is a lack of research in horses. This study aimed to determine how blood sample storage methods influence CBC parameters. The hypothesis of this study was that key factors in hematology sample storage, namely temperature and time elapsed from collection to analysis, affect CBC parameters. Blood samples were collected from 10 healthy Quarter Horse mares (age: 13 ± 4.5 yr) and stored in EDTA tubes at room temperature (22°C), refrigerated (4°C), above ice (8°C), or in contact with ice (2°C). The IDEXX ProcyteDx was used to obtain CBCs at 3, 6, 12, 24, 48, and 72 h after collection. Data were analyzed using the Kruskal-Wallis test with Dunn's post hoc analysis and Benjamini-Hochberg correction for multiple comparisons. Significance was set to P < 0.05. Hematocrit increased in all treatments by 2% by 48 h (P < 0.01). Mean corpuscular volume increased in all treatments by 2 to 3 fL by 48 h (P < 0.01). Red blood cell distribution width increased by 2% to 3% by 48 h in all treatments (P < 0.01) and was overall 2% lower at 22°C compared with all other storage temperatures (P < 0.01). Platelet count did not change over time at 22°C but increased by 205 to 217 K/µL by 72 h at 8°C (P < 0.01), 232 to 259 K/µL by 72 h at 4°C, and 66 to 67 K/µL by 24 h at 2°C (P < 0.01). Mean corpuscular hemoglobin concentration decreased by 1 to 3 g/dL in all storage conditions by 48 h (P < 0.01), and samples kept in 22°C decreased 2 g/dL further by 72 h compared with 48 h (P < 0.01). Both the percentage and number of monocytes decreased by 1% and 0.1 K/µL, respectively, by 72 h at 22°C (P = 0.04, P = 0.01, respectively) with no changes across time points observed at other storage temperatures. Both the percentage and number of basophils were 0.3% to 0.4% and 0.03 to 0.04 K/µL higher in samples stored at 22°C compared with all other storage temperatures (P < 0.01, P < 0.01, respectively). These findings suggest that blood samples should be processed within 24 h when stored at 8°C, 4°C, or 2°C. However, storing samples at room temperature is recommended if platelet count is of primary interest. This study provides evidence to benefit CBC analysis standards of practice and emphasizes the importance of considering storage conditions when evaluating hematological parameters both in practice and research, allowing for the potential to accurately obtain CBCs in various environments.