Blood from a "half-fish" dog: How modern analyzers deal with nucleated red blood cells

Validation of the Sysmex XN-V Automated Nucleated Red Blood Cell Enumeration for Canine and Feline EDTA-Anticoagulated Blood

The enumeration of nRBCs (nucleated red blood cells) by manual counting is time-consuming and imprecise. As the first veterinary hematology analyzer, Sysmex XN-V provides automated nRBC counts. This study aimed to evaluate the performance of Sysmex XN-V in the enumeration of nRBCs for cats and dogs by comparing automated nRBC counts to manual counts from a total of 3810 canine and 2844 feline specimens. Repeatability, reproducibility, stability, carry-over, and linearity were assessed. The repeatability and reproducibility of Sysmex XN-V were good, with mean coefficients of variation (CV) of 4.5% and 5.4%, respectively. Bland-Altman difference analysis revealed mean biases shown as nRBCs/100 WBCs of 0.01 in dogs and 0.11 in cats with low nRBCs (<5/100 WBCs), mean biases of -1.27 in dogs and -0.24 in cats with moderate nRBC counts (5-20 nRBCs/100 WBCs), and mean biases of -7.76 in dogs and -1.31 in cats with high nRBC counts (>20 nRBCs/100 WBCs). The total observable error was below 9% in both species and at all ranges. Overall concordance between methods was high (91% in canine and 93% in feline samples). The automated nRBC count by Sysmex XN-V was found to be accurate and precise and can replace manual counts for cat and dog samples. Non-statistical quality assurance by scattergram evaluation, re-gating, and confirmation by blood smear evaluation is, however, recommended, especially in cases with severe normoblastosis. This advancement will save time, reduce errors, and add prognostic value to hematological results for animal patients.

Analytical errors in nucleated red blood cell enumeration

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.