Analytical errors in nucleated red blood cell enumeration

• Published in: Veterinary clinical pathology 2023-12, Vol.52 (4), p.554-568
• Main Authors: Brown, Juliet E., Oscos‐Snowball, Astrid, Courtman, Natalie F.
• Format: Article
• Language: English
• Subjects: Animals; Automation; Blood; Cat Diseases; Cats; Dog Diseases; Dogs; error; Erythroblasts; Humans; Leukocytes; metarubricytosis; normoblastosis; Reproducibility of Results; Retrospective Studies; rubricytosis; Sysmex; WNR
• ISSN: 0275-6382; 1939-165X
• DOI: 10.1111/vcp.13224

Background Enumeration of nucleated red blood cells (NRBCs) in peripheral blood of dogs and cats is performed by manual counting during blood film evaluation. Automated methods have increased precision and accuracy; however, most analyzers cannot distinguish leukocytes and NRBCs. The Sysmex XN‐V Series may distinguish NRBCs and leukocytes; however, analytical errors occur. Objectives We aimed to investigate cases with discrepant automated and manual NRBC counts, and to evaluate reasons for analytical errors. Methods Data from samples with increased NRBCs were collected retrospectively and compared with manual counts performed on blood films using Spearman's correlation, Passing‐Bablok agreement analysis, and Bland–Altman comparisons. Precision of the automated method and interobserver agreement of manual counts were evaluated. Cases with discrepant results were investigated. Results Agreement between the methods was good at ≤1NRBC ×109/L in dogs and cats, and inadequate at ≥1NRBC ×109/L. The automated method demonstrated a negative proportional difference to the manual method. Precision was good for the automated method (overall CV 7.1%) and interobserver agreement for the manual method was poor overall (mean CV 27.3%, range 0%‐106.1%). Inaccuracies in NRBC enumeration by the automated method occurred with high hematocrits, the mergence of the cell fragments and leukocyte clouds, and the presence of earlier erythroid precursors. Conclusions NRBC enumeration by the WNR channel on the Sysmex XN‐1000 V is precise and has good agreement with manual counts in canine and feline blood samples at ≤1NRBC ×109/L. Manual film review is indicated for samples with ≥1NRBC ×109/L, earlier erythroid precursors, samples from greyhounds and dehydrated patients, and if gating errors are noted.