Fragility of leucocytes in chronic lymphatic leukaemia.

Sir, The occurrence of a grossly incorrect result for the 'total leucocyte count' was observed in a case of chronic lymphatic leukaemia when this figure was estimated using the Coulter counter model A with the 'saponin' method of lysing the red cells. In this particular case, the total leucocyte count was estimated in two ways: (a) by taking blood samples in duplicate for the Coulter instrument, and (b) by taking blood samples in duplicate for the visual method using accurate B.S.S. 748 white cell dilution pipettes, with 2% acetic acid as the diluent and counting the cells on a double-ruled improved Neubauer haemacytometer, amended B.S.S. 748 (1958). The four-coiner square millimetre areas on each side of the haemacytometer were counted for the visual method and six separate counts were made on each of the two Coulter samples. The Coulter counts were made 10 minutes after the addition of 0.1 ml. of a 2% solution of saponin (B. D. H. White), at an instrument threshold setting of 40. The results of the Coulter counts, after correction for the blank were: 7,568, mean for the six counts on blood sample no. 1, and 8,116, mean for the six counts on blood sample no. 2, giving a final mean for both blood samples of 7,842 leucocytes per c.mm. of whole blood. The results for the visual counts were 17,400 and 15,700 respectively, giving a final mean for both samples of 16,550 leucocytes per c.mm. of whole blood. Previous counts on this individual carried out at two-monthly intervals, using the same methods, have not shown this phenomenon, neither didany of the total leucocyte counts made at the same time on other individuals, using the same diluting and saponin solutions. The leucocytes seen on the haemacytometer counting chamber were well-defined cells and apparently not degenerate types; the stained blood film, however, did show approximately 50% of the leucocytes to be smear or basket cells, suggesting a high degree of degeneration or fragility of the leucocytes. It seems probable that the saponin solution used for lysing the red cells when making the total leucocyte counts also lysed many of the leucocytes in this particular case and it may be that as the condition advances the leucocytes become more fragile. It has also been suggested that since the lymphocytes in this condition are of the very small type, many may be missed when counting leucocytes with a threshold setting used for normal white cell counts. Although this may be an observation ofno significance, it would be interesting to leam if others have experienced similar findings. C. SANDERS Clinical Pathological Department, A.E.R.E., Harwell, Didcot, Berks. CAUTIONARY TALE