An automated method for thrombocyte counting in capillary microsamples.

Introduction: We aimed to develop an automated, low-volume method for thrombocyte counting in capillary blood using the Sysmex predilution (PD) mode.

Methods: Microsamples were prepared by resuspension of 50 μL blood in 300 μL DCL CellPack. Thrombocyte counting was done in the impedance (PLT-I) and fluorescence (PLT-F) channels. The imprecision and bias was evaluated in >394 microsamples from adult blood. Preanalytical factors (skin-piercing, storage, and transportation in our pneumatic tube system) was assessed, and studies on pediatric microsamples were made for comparison. The improvement in analytical quality and turnaround time was examined.

Results: For PLT-F, the imprecision was 1.1%-3.7%, and the bias was 10.1% (95% CI: 8.8-11.3). After skin-piercing, the bias was 8.1% (95% CI: 5.6-10.6) and the imprecision 1.9% (95% CI: 1.3-2.5). Thrombocyte counts kept stable after 4 h at room temperature (94.8% [95% CI: 93.2-96.4]) and after pneumatic tube transportation [6.7% (95% CI: 4.8-8.6)]. The bias of the PD mode for pediatric microsamples was 13.0% (95% CI: -8.4-34.4) in the PLT-F channel. The automated method had a considerably lower imprecision than the existing manual thrombocyte counting method and reduced turnaround times.

Conclusion: The automated microsample method offers a low-volume alternative for measurement of thrombocytes. The method appears useful also in pediatric samples.