Background: The count of argyrophilic nucleolar organizing regions (AgNOR) has been considered a useful variable that reflects cellular proliferation in canine lymph nodes, but it has not been compared with other markers of proliferation.
Hypothesis: Ki67 and AgNORs are equally useful as markers of tissue proliferation in fine needle aspirates of canine lymph nodes.
Animals: A total of 101 dogs.
Material and methods: Prospective, observational study of a convenience sample of dogs. Two smears were prepared for a May-Gruenwald-Giemsa stain and a Ki67/AgNOR double stain. In addition, CD3/CD79a immunostaining was performed when cytologic examination revealed a lymphoma. The dogs were grouped as normal (n = 26), reactive hyperplasia (n = 25), lymphadenitis (n = 31), and lymphoma (n = 19), based on the physical examination and the cytologic findings. The AgNOR count/cell, AgNOR area/cell and the percentage of cells staining positive for Ki67 were evaluated in 100-167 cells (median, 113 cells) by using automatic image analysis.
Results: Mean (SD) AgNOR counts/cell were 1.36 +/- 0.19 in normal dogs, 1.55 +/- 0.26 in lymphadenitis, 1.65 +/- 0.32 in reactive hyperplasia, and 3.67 +/- 1.08 in lymphoma. The percentage of Ki67 positive cells was 2.67 +/- 0.99% in normal lymph nodes, 5.04 +/- 3.34% in lymphadenitis, 5.36 +/- 2.14% in reactive hyperplasia, and 30.2 +/- 10.8% in lymphoma. All variables were significantly higher in dogs with lymphoma compared with the other groups (P < .0001). The sensitivity and the specificity of the AgNOR count for diagnosing lymphoma were 95 and 96% at a cutoff value of >2.04 AgNORs/cell. The cutoff value for the Ki67 positive cells was >10.40% (sensitivity, 95%; specificity, 98%).
Conclusion and clinical importance: The results indicated that both AgNOR and Ki67 counts were good diagnostic tools for assessment of proliferation in aspirates of canine lymph nodes.