The diagnostic utility of lymph node cytology samples in dogs and cats

OBJECTIVES The aim of this study was to determine common reasons for lymph node fine needle aspirates, cytological diagnoses reported and the frequency and reasons for non‐diagnostic samples from dogs and cats. METHODS Retrospective study of computerised records of fine needle aspirate samples submitted to NationWide Laboratories (UK) between April 2009 and May 2011 to identify lymph node samples. Reason for sampling, sample quality, diagnosis achieved and reason for non‐diagnostic samples were assessed. RESULTS A total of 1473 records were available for review. Of 1274 canine samples, 928 (72 · 8%) were diagnostic and 346 (27 · 2%) were non‐diagnostic. Of 199 feline samples, 171 (85 · 9%) samples were diagnostic and 28 (14 · 1%) were non‐diagnostic. The most common reasons for sample submission in both species were investigation of lymphadenopathy (alone or in combination with other clinical signs) or tumour staging. In dogs, the most common diagnosis was lymphoma (351, 27 · 5%), and in cats, reactive hyperplasia (63, 31 · 6%). Absence of cells, cell disruption and low yield were the most common causes of non‐diagnostic samples. Submission of the history did not affect the probability of reaching a cytological diagnosis. CLINICAL SIGNIFICANCE Lymph node cytology is a useful diagnostic procedure but educating veterinarians to improve sampling and smearing may increase diagnostic yield.