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Diagnostic Value of LN FNA

Clinician's Brief (Capsule)

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Lymph node (LN) cytology is an accessible, inexpensive test with good sensitivity and specificity, albeit with intrinsic limitations. This retrospective study aimed to describe common indications for LN fine needle aspirates (FNA) and reported cytological diagnoses as well as frequency and explanations for nondiagnostic samples from dogs and cats. FNA sample records were evaluated for sampling, sample quality, diagnosis achieved, and reason for nondiagnostic samples. It was hypothesized that samples with clinical history provided and greater number of slides submitted would increase likelihood of diagnosis.

In the 1473 records reviewed, the most common reasons for aspirate submission were investigation of lymphadenopathy or tumor staging. In dogs, 72.8% of samples were diagnostic; in cats, 85.9%. In dogs, the most common diagnosis was lymphoma, followed by reactive hyperplasia. In cats, most common was reactive hyperplasia, followed by lymphoma; however, only 50% of these lymphoma cases were confidently diagnosed, compared with 73% in dogs. The most common causes of nondiagnostic samples were absence of nucleated cells, cell disruption, and low cell yield. Submission of clinical history did not correlate with likelihood of reaching diagnosis. In dogs, submission of a higher number of slides was correlated with a higher likelihood of a diagnostic sample and cytological diagnosis. Educating practitioners on improved sample collection, smearing technique, and in-house sample examination before submission may increase diagnostic value of LN FNA.

Global Commentary

This study, which involved submission of nonstained samples with the standard staining in the laboratory, clearly demonstrates that LN cytology is highly diagnostic. Nondiagnostic samples were the result of either sampling or smear-preparation technique. In most clinical settings, slightly more nondiagnostic samples may be expected because of poor staining. There is no reason, however, to consider that the LN cytology is of low diagnostic yield. If the result is nondiagnostic because of the sample preparation, a clinician can repeat the procedure for better sampling. If it is nondiagnostic because of the nature of the lesion, the clinician can turn to surgical resection and histopathology. This is a low-risk, high-return procedure.—Takuo Ishida, DVM, PhD, DJCVP (Japan)

This capsule is part of the WSAVA Global Edition of Clinician's Brief.

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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