The significance of leukemia and lymphoma cells in cerebrospinal fluid contaminated by blood containing malignant cells: A probabilistic approach based on the poisson frequency distribution

The significance of malignant cells in a body fluid is often difficult to determine if that fluid is contaminated by blood containing malignant cells. This problem is most often seen in examination of CSF from patients with lymphoma or leukemia. We suggest a statistical model of this problem in which the numbers of malignant cells in the blood and the fluid specimen are related to the number of red blood cells. Using the Poisson distribution, the probability of finding the observed number of malignant cells in the fluid is calculated and used as the basis for suggesting whether these cells are likely to represent contamination effect or true involvement of the fluid by the malignancy. The limitations and applicability of this process are discussed.