Automated Red and White Blood Cell Counting in Capillary Microsamples by Sysmex-XN Predilution Mode

Neonatal patients present a challenge to the clinical laboratory because of their low blood volume. The Sysmex XN-series features a predilution (PD) mode allowing hematologic measurements with only 20-50 μL of blood. We verified the PD mode for analysis of selected hematologic parameters in 50 μL microsamples.

Microsamples were prepared from adult EDTA blood. White blood cell count (leukocytes, neutrophils, and lymphocytes) and red blood cell parameters (erythrocytes, hemoglobin, hematocrit, mean cell volume, and reticulocytes) were evaluated. The imprecision of the PD mode was evaluated over 3 days, and the accuracy was assessed by method comparison with the standard whole blood mode. The effect of capillary sampling, microsample stability during storage, and pneumatic tube transportation was evaluated. Finally, the bias was reproduced in a small sample of pediatric patients.

For white blood cells, the bias was ≤ 5.4% (95% CI: 4.5-6.2) and imprecision was below 3.5% (except at the lowest levels). Capillary sampling had little effect on PD analytical performance (bias ≤ 0.7% and imprecision ≤ 4.7%) and white blood cell counts were stable for 7 h at room temperature and after pneumatic tube transportation. The red blood cell parameters generally exceeded the allowable bias and imprecision. The bias of the pediatric samples remained within the 95% PI for the method comparison studies.

The PD mode has acceptable analytical performance and preanalytical stability for white blood cell counts but not for red blood cell parameters. It may offer a low-volume alternative for hematologic monitoring.