[Possible errors in leukocyte count caused by carryover in the Coulter counter S]

In 163 samples of venous blood with significant leukocytosis (20 000 to 172000 cells pro mm-3) a carryover of 400 to 22000 leukocytes up to the third count of the following specimens (200 to 9300 cells/mm-3) could be observed. Even after 41 specimens of normal leukocyte range and low leukocytosis (6700 to 17700 cells/mm-3) in cases of extreme leukopenias (less than 2000 cells/mm-3) the correct result was exceeded by 500 to 1000 cells. In four additional machines of other laboratories a carryover of different extent could be reproduced. In comparison to samples of venous blood only a very small carryover into subsequent samples of isotonic solution was found. The considerable spreading of the coefficient of variation between 1.7 and 16.2% (arithmetic mean 7.1%) prohibited a mathematical correction of error. Erroneously too high numbers of leukocytes could be absolutely avoided by at least two repeated counts.