The utility of reticulocyte indices in distinguishing iron deficiency anemia from anemia of inflammatory disease, portosystemic shunting, and breed-associated microcytosis in dogs.

Abstract

Indices of reticulocyte cell size and hemoglobin content show promise for diagnosing iron deficiency (FeDef), but have not been evaluated in other causes of canine anemia or microcytosis. The aims of this study were to establish reference intervals (RI) for reticulocyte indices in dogs, and to compare results from dogs with FeDef anemia to dogs with 3 conditions that may mimic FeDef on hematologic and biochemical testing, including anemia of inflammatory disease (AID), portosystemic shunting (PSS), or breed-associated microcytosis (BAM). Reticulocyte indices were measured using the ADVIA 2120. Reference intervals were determined prospectively in 122 healthy dogs, and retrospectively compared between dogs with FeDef (n=11), AID (n=12), PSS (n=12), and BAM (n=7). Almost all dogs had at least one reticulocyte index outside the RI. The most discriminating reticulocyte indices were reticulocyte hemoglobin concentration (CHCMr) (FeDef≤26g/dL, AID≥26g/dL, PSS≥24.1g/dL, and BAM≥27.7g/dL), reticulocyte hemoglobin content (CHr) (FeDef≤20.1pg, AID≥21.8pg, PSS≥19.2pg, BAM≥21pg), percentage of reticulocytes with low CHCMr (%Hypo-r) (FeDef≥74.2%, AID≤80.1%, PSS≤91.5%, BAM≤61.6%,), and percentage of reticulocytes with low CHr (%LowCHr) (FeDef≥50.7%, AID≤31.3%, PSS≤63.2%, BAM≤34.1%). Reticulocyte indices can be altered in dogs with various conditions, and are not specific for FeDef. Dogs with CHCMr, CHr, %Hypo-r, and %LowCHr beyond the above cutoffs are suspicious for FeDef. Dogs with AID, PSS, or BAM with reticulocyte indices altered beyond the ranges reported for those subgroups warrant evaluation for concurrent iron deficiency.