The relationship between chronic lymphocytic leukaemia and prolymphocytic leukaemia. III. Evaluation of cell size by morphology and volume measurements.

The peripheral blood WBC size distribution was assessed by morphological and volume measurements in 73 patients with B-cell chronic lymphocytic leukaemia (CLL) and prolymphocytic leukaemia (PLL). Patients with typical CLL, with less than or equal to 10% prolymphocytes, had a homogeneous major population of small cells which could be recognized both by morphology and volume (median volume 211.5 +/- 32.5 fl). In PLL, the volume of the main cell component was significantly larger than in CLL: in two-thirds of cases the major cell population was distributed in a first lognormal fitted curve of the volume histogram, with median volume 281.8 +/- 38.0 fl; in the remaining cases the main cell component showed a larger median volume (353.5 +/- 71.9 fl) contained within the second lognormal curve which was preceded by a minor peak. CLL patients with 11-55% prolymphocytes (CLL/PL) had characteristic cell volume histograms in which two lognormal curves could always be fitted: in 80% of cases the main cell component was located in a first curve with median volume of 257.9 +/- 28.6 fl; in the remaining cases the major population was represented by cells with median volume of 349.0 +/- 83.9 fl distributed in a second peak. Although in both CLL and CLL/PL the majority of cells was defined morphologically as small, the median volume of these lymphocytes was significantly larger in CLL/PL. The degree of concordance in the assessment of cell size between morphology and volume measurements was high in CLL, whereas in CLL/PL and PLL morphology underestimated the cell size of the major population, compared with its actual volume, in over 50% of cases. We conclude that the identification of prolymphocytes as larger cells in blood films may be hampered by distortions and artefacts of spreading. Volume measurements may provide a more objective indicator of the cell populations in this group of disorders.