LAUSR

BACKGROUND A novel method using a moving threshold (r-PLTmt) to determine canine r-PLTs (reticulated platelets) has been introduced for ADVIA 2120 software v6.11.7. OBJECTIVES We aimed to evaluate absolute (ar-PLTmt) and percent (%r-PLTmt) prior to and after visual inspection of scattergrams (ar-PLTmtv, %rPLTmtv) compared with flow cytometry (flow) and to determine reference intervals (RIs) in 120 dogs. METHODS For method comparison, 42 blood samples of healthy and thrombocytopenic dogs were included. Calculation of Spearman's rho, Bland-Altman, and Passing-Bablok analysis was performed. Coefficients of variation (CVs) were determined for three concentration levels. RESULTS Moderate correlations between %r-PLTmt and %r-PLTmtv (rs 0.75-0.76) were seen compared with flow cytometry. The CV for medium %r-PLTs counts assessed with flow cytometry was 12.9%. Comparable CVs were obtained for ar-PLTmt (14.4%) and %r-PLTmt (15.7%), and ar-PLTmtv and %r-PLTmtv (10.9% and 12.9%, respectively). At low and high concentration levels, CVs for % and absolute r-PLTmt/rPLTmtv ranged between 23%-30% and 15%-20%. In patients with microcytic hypochromic erythrocytes, CVs for ar-PLTmt and %r-PLTmt were 36%-66%. Visual inspection of scattergrams resulted in a marked decrease in CV ranging between 15% and 20%. A proportional bias of 10.8% between %r-PLTmt and flow cytometry became lower (9.7%) after visual validation of scattergrams. Passing-Bablok analysis showed proportional and constant error. RIs for r-PLTmt and r-PLTmtv were 0.2%-3.8% and 0.6-10.2 × 109 /L and 0.3%-4.5% and 1.1-10.3 × 109 /L, respectively. Median values for %r-PLTmtv were higher in young adults (≤2 years) than in older dogs (P = 0.03). CONCLUSIONS r-PLTmt and r-PLTmtv were moderately correlated with flow cytometry. Visual inspection of scattergrams is recommended.