Hematological Parameters in Rabbits: A Meta-Analysis of Compiled Reference Data and Confounding Factors

Background: Numerous studies have investigated reference values for hematological parameters in rabbits and their confounders. However, the results vary widely due to differences in the populations of animals studied, environmental conditions and measurement methods. Currently, a comprehensive summary of these studies is lacking, which makes it difficult to keep track of the different reference values. Objectives: This article aims to compile and summarize standardized reference values for common hematological parameters in rabbits, and to identify significant confounders. Methods: A systematic review and statistical analyses of 144 studies involving 9631 rabbits published worldwide between 1920 and 2023 was conducted. Multiple meta-analyses were performed to aggregate published reference data and identify significant confounders for each hematological parameter. Results: Pooled estimates of reference values were calculated for the following hematological parameters: red blood cell count (RBC), hematocrit (HCT), hemoglobin (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), red cell distribution width (RDW), reticulocyte count, white blood cell count (WBC), lymphocyte, eosinophil, basophil, monocyte and platelet (PLT) counts, mean platelet volume (MPV) and plateletcrit (PCT). Age, sex, pregnancy status, season, housing condition, measurement material, and the measurement method were identified as significant confounders (P < 0.05; Cohen's d > 0.5). Conclusions and clinical relevance: This review provides a statistical summary of standardized reference values, which will aid in the interpretation of blood test results in veterinary practice and research. It emphasizes the importance of considering demographic, seasonal, environmental and methodological factors when analyzing hematological data in rabbits.