Sensitivity and specificity of manual and automated measurements of reticulocyte parameters for classification of anemia in dogs: 174 cases (1993–2013)

OBJECTIVE To assess sensitivity and specificity of manual and automated measurements of reticulocyte percentage, number, and production index for classification of anemia in dogs. DESIGN Retrospective case series SAMPLE 174 blood smears from client-owned dogs with anemia collected between 1993 and 2013 for which reticulocyte parameters were determined manually (nonregenerative anemia, 22; preregenerative anemia, 23; regenerative anemia, 28) or with an automated laser-based counter (nonregenerative anemia, 66; preregenerative anemia, 17; regenerative anemia, 18). PROCEDURES Diagnostic performance was evaluated with receiver operating characteristic (ROC) curves by considering preregenerative anemia as nonregenerative or regenerative. Sensitivity, specificity, and positive likelihood ratio were calculated by use of cutoffs determined from ROC curves or published reference limits. RESULTS Considering preregenerative anemia as non regenerative, areas under the curve (AUCs) for reticulocyte percentage, number, and production index were 97%, 93%, and 91% for manual counting and 93%, 90%, and 93% for automated counting. Sensitivity, specificity, and positive likelihood ratio were 82% to 86%, 82% to 87%, and 4.6 to 6.4, respectively. Considering preregenerative anemia as regenerative, AUCs were 77%, 82%, and 80% for manual counting and 81%, 82%, and 92% for automated counting. Sensitivity, specificity, and positive likelihood ratio were 72% to 74%, 76 to 87%, and 2.7 to 6.2, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Whereas all reticulocyte parameters identified regeneration in anemic dogs, the performance of specific parameters was dependent on the method used. Findings suggested that lower cutoffs than published reference limits are preferred for reticulocyte number and production index and higher cutoffs are preferred for reticulocyte percentage. Reticulocyte production index may be useful when the pretest probability of regeneration is moderate.