Automated counting of white blood cells in synovial fluid.
OBJECTIVE
To evaluate the performance of automated leucocyte (white blood cell; WBC) counting by comparison with manual counting.


METHODS
The number of WBC was determined in heparinized synovial fluid samples by the use of (i) a standard urine cytometer (Kova) and a microscope (reference method) and (ii) a haematology analyser (Sysmex XE-2100; WBC/BASO and DIFF channels). Imprecision within and between days was determined by replicate analysis of a low (level A; WBC approximately 0.560 x 10(9)/l) and a high (level B; WBC approximately 1.081 x 10(9)/l) dedicated synovial fluid control (Quantimetrix).


RESULTS
The WBC count of the DIFF channel was highly correlated with the WBC count of the microscopic reference method (r = 0.99; WBC analyser = 0.870 x WBC reference method + 0.413). In contrast, no agreement existed between WBC counts generated by the WBC/BASO channel of the analyser and the reference method (r = 0.52; WBC analyser = 0.008 x WBC reference method + 0.079). Within-day imprecision (4-7%) and between-day imprecision (10%) of the haematology analyser were smaller than the within-day imprecision (12%) and the between-day imprecision (20-22%) of the manual reference method. For manual counting, inter-observer coefficients of variation were 35.9% (control level A) and 21.0% (control level B).


CONCLUSIONS
The WBC count in synovial fluid can be reliably determined using the DIFF channel of the Sysmex XE-2100. Automated counting of WBC in synovial fluid offers more precise and faster results than manual counting.
de Jonge
R
R
Department of Clinical Chemistry, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands. r.dejonge@erasmusmc.nl
Brouwer
R
R
Smit
M
M
de Frankrijker-Merkestijn
M
M
Dolhain
R J E M
RJ
Hazes
J M W
JM
van Toorenenbergen
A W
AW
Lindemans
J
J
D001168:Arthritis / Q000175:diagnosis*; D003581:Cytodiagnosis / Q000295:instrumentation / Q000379:methods; D005434:Flow Cytometry; D006801:Humans; D007958:Leukocyte Count / Q000295:instrumentation; D016014:Linear Models; D008853:Microscopy; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000379:methods; D013582:Synovial Fluid / Q000166:cytology*