An important consideration is the setting of the
threshold for a positive blood smear or bone marrow
cytology. In this study, the cut-off of 10% large lymphocytes
was chosen based on the pathologist’s confidence
in discerning the presence of neoplastic cells on
microscopic examination, given specific visual criteria.
By choosing a specific cut-off value, we are able to uniformly
asses and compare the samples. Universally
accepted criteria for the identification of neoplastic
cells based on visual assessment of blood and bone
marrow smears have yet to be established. Previous
studies on canine lymphoma either did not define cutoff
values or used values ranging from one to 20% neoplastic
cells.5,13,15,16 Not only is the identification of a
positive blood or bone marrow smear dependent on
the cut-off value for defining a positive smear, it also
relies on the skill of the individual interpreting the
smear. Our conclusions presume that an experienced
individual trained in clinical pathology will make these
assessments. In clinical practice, this would require
that blood smears be sent to a diagnostic reference
laboratory.