The Effects of Size of Sampling Area and Dilution on Leucocyte Counts in a Hemocytometer

With nearly 5000 areas examined, the comparison of a Poisson distribution to the distribution of leucocytes in a hemocytometer chamber at both 1:100 and 1:25 dilutions indicated a poor fit (P= <0.0001), a non-random distribution. In a series of leucocyte determinations from a young, male university student comparing 28 counts from 18 mm (both chambers) with 28 from 9 mm, and 28 from 4 mm (the usual standard), the mean from the 18 mm counts was not significantly different from that of the 9 mm counts. However, both the means of the 18 mm counts and the 9 mm counts were significantly different from that of the 4 mm counts (P = 0.02 and 0.035 respectively). Forty-two counts at 1:100 dilution had a mean not significantly different from that of 42 counts at 1:20 dilution (P = 0.06). It appears that the counts from the 18 mm area at 1:100 dilution are the most reliable and are therefore recommended for critical research determinations. Fourteen such counts had the most restricted range and the lowest standard deviation of any of the six combinations.