Effect of storage on microcytosis observed in dogs with portosystemic vascular anomalies

Microcytosis is a common laboratory finding in dogs with iron deficiency and congenital portosystemic vascular anomalies (PSVA), however artefactual changes due to blood storage may occur which could mask this feature. This study evaluated the effects of storage on microcytosis in dogs with congenital PSVA. Full haematological parameters were measured on the day of sampling and following 24 h storage at room temperature, in unaffected dogs (n = 13) and in dogs affected with PSVA (n = 24). Storage for 24 h resulted in significantly higher MCV values in both groups of dogs (P < 0.01). The percentage increase in MCV was greater in the control dogs (median 8.07%, range 5.64–9.31%) compared to affected dogs (median 6.05%, range 3.12–15.21%) (P < 0.02). Storage of 1 ml EDTA blood samples at ambient temperature for 24 h prior to analysis, as occurs when samples are posted to external laboratories, will have significant effects on MCV and may mask microcytosis in dogs with PSVA.