F. KILIC¹, N. GRETHER¹, D.A. TSAKIRIS<sup>1

1</sup>Diagnostic Hematology, University Hospital Basel, Switzerland

BACKGROUND:

In our laboratory CSF cell counts are traditionally performed by manual microscopy using the Fuchs–Rosenthal counting chamber. This procedure is time-, labour- and cost-intensive and requires experienced laboratory staff. Alternatively, there are several automated hematology analyzers to quantify the total cell count. Interestingly, in external quality control programs manual cell counts have always been less successful as the automated ones.

Is actually the manual method obsolete for CSF samples, which typically have low cell counts, often less than 50 cells/μL? The objective of this study was to evaluate the correlation and agreement of cell count and differentiation among Fuchs-Rosenthal chamber and automated method using Sysmex XN-1000 as an analyzer.

METHODS:

Sysmex XN-1000 offers automated standardized quantification of white blood cells (WBCs) in body fluids (BF), with differentiation of polymorphonuclear cells (PMNs) and mononuclear cells (MNCs). Comparison of WBC, PMN and MNC between the manual and the automated method was performed for 241 CSF samples. To study the ability to discriminate between PMNs and MNCs, 24 cytospin slides were prepared, air dried and stained using RAL Stainer MCDh reagent.

All CSF samples were measured within 2 hours after sampling. The specimens were counted manually (after staining with Samson’s reagent) in the Fuchs-Rosenthal chamber and analyzed on the Sysmex XN-1000 simultaneously.

Results:

The Passing & Bablok correlation was good between manual and automated leukocyte counts (r²=0.97). At low cell counts <20 cells/μl the correlation was weaker (r²=0.75) but the absolute Bias obtained by Blant Altman Plot had the amount of only 0.8 cells/μl. For manual WBC range of 0 to 5 cells/μL the corresponding Sysmex 0 to 95th percentile range is 0 to 6 cells/μL.

The intra-assay variation (mean CV %) for total low cell count <20 cells/μl in CSF of the Sysmex XN-1000 was 9.8%.

Overall agreement between the XN-1000 and cytospin slides was observed concerning differentiation in PMN and MNC.

Conclusions:

Due to high imprecision at low WBC counts (<20 cells/μl) and good agreement with the manual method, the XN-1000 is a favourable alternative to the labour-intensive, time-consuming and potentially less reliable manual counting.

Further analysis of the automated flagging algorithms for abnormal cell distributions in body fluid samples is needed and will help define criteria for microscopic review.