A Study on the Counting and Expressing Method of Erythrocytes Observed in Sediment by Centrifuging Fresh Urine

Abstract

In the microscopic examination of blood red cells in urine sediment, there is no standardized method in terms of how many visual fields should be observed or how the results should be expressed. In order to determine such standards, samples from fifteen students were collected and red blood cells in the sediment of the urine were observed approximately 100 times through a high power microscope. When the mean number of red blood cells per visual field is three or less, the number of such cells in each visual field shows a Poisson distribution. Here, observing 20 visual fields is sufficient to count red blood cells in a routine examination, since the 95% confidence interval of the mean is narrowed when 20 visual fields are examined. In this case, only the mean number of red blood cells needs to be expressed. However, when the mean is greater than three, the number of red blood cells in each visual field shows a Pólya-Eggenberger distribution, because some visual fields may contain aggregated red blood cells, making the variance greater than the mean. In this case, 20×C visual fields should be examined (where C is the value of variance/mean), and the results should be expressed using the variance as well as the mean.