Point-of-care method for total white cell count: an evaluation of the HemoCue WBC device

Abstract

Point-of-care testing (POCT) is becoming an important adjunct to haematology laboratory practice. An important component of the blood count is the total white cell count (WBC). Previously, this required laborious microscopic cell counting, but it can now be performed by means of automation; however, in many under-resourced countries, costly automated counters are only available in very few central hospitals. Moreover, neither method is practical in most POCT situations. The HemoCue WBC has been developed as a simplified alternative method, consisting of a reagent pre-loaded disposable cuvette together with basic image analysis technology. This report describes an assessment of its utility. The WBC of 500 routine blood samples from the hospital were tested in parallel by the HemoCue WBC and by a reference analyser to assess accuracy and utility of the former. The tests included precision, linearity, type of blood sample and anticoagulant and potential interfering substances in blood specimens. In the tests for accuracy, 192 of the 200 showed percentage difference from the NEQAS reference of <10% whilst the remaining eight samples differed by <12%, thus meeting the requirements of Clinical laboratory improvement amendments (CLIA)-88 regulations. Of the samples tested with potential interfering substances only those with >2% normoblasts or reticulocytosis showed significant differences from the reference measurements. The HemoCue WBC is reliable for WBC counts within the analytical range of 0.4-30.0 x 10(9)/l, except in samples where there are significant numbers of normoblasts or reticulocytes. It is simple to use and provides a valuable advance in the facilities available for POCT in haematology.

Figure 2

Microscopic appearance of a cuvette filled with a blood sample. (×40) Photographed on a conventional light microscope (Nikon E400; Nikon Electronic Company, Osaka, Japan).

Figure 1

Photograph of the portable HemoCue WBC Point-of-care analyser (plastic cuvette containing a drop of blood is shown placed on the circular base holder).

Figure 3

Correlation between the reference analyser and the HemoCue WBC. Y = 0.989X−0.082 (Y = reference analyser and X = HemoCue WBC). The correlation coefficient (r) between 0.4 × 10⁹/l and 30 × 10⁹/l = 0.997. These findings indicate good comparability within the manufacturer’s suggested analytic range with no detectable bias.

Figure 4

Comparison of HemoCue WBC measurements on capillary and venous blood samples: