Diagnostic accuracy of using erythrocyte indices and polychromasia to identify regenerative anemia in dogs.

OBJECTIVE

To determine diagnostic accuracy of using erythrocyte indices and polychromasia to identify regenerative anemia in dogs.

DESIGN

Retrospective and prospective cross-sectional study.

ANIMALS

4,521 anemic dogs.

PROCEDURES

CBC results obtained between July 2002 and July 2008 by use of an automated laser-based flow cytometric hematology analyzer from dogs with Hct values ≤ 35% were retrieved. Sensitivity, specificity, accuracy, and predictive values of using erythrocyte indices and polychromasia to identify regeneration were determined, with a reticulocyte count > 65,000 reticulocytes/μL considered the gold standard. Similarly, 134 blood samples from anemic dogs were analyzed prospectively with an in-house electrical impedance analyzer.

RESULTS

Of 4,387 dogs with samples analyzed retrospectively, 1,426 (32.5%) had regenerative anemia. Of these, 168 (11.8%) had macrocytic hypochromic anemia. High mean cell volume and low mean cell hemoglobin concentration had low sensitivity (11%), high specificity (98%), and moderate accuracy (70%) when used to identify regenerative anemia. Use of polychromasia alone had an accuracy of 77%, and use of polychromasia combined with a high RBC distribution width (RDW) had an accuracy of 79%. Results obtained with the in-house analyzer were similar.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that most regenerative anemias in dogs were not macrocytic hypochromic. Polychromasia, with or without high RDW, was a more accurate indicator than other erythrocyte indices of regenerative anemia. To avoid a false diagnosis of nonregenerative anemia, a blood smear should be evaluated in anemic dogs when a reticulocyte count is not available.