Which laboratory test can help confirm the diagnosis of lymphoma?

Cytology is a key laboratory test used to confirm the diagnosis of lymphoma because it involves obtaining samples of tissue or fluid from affected areas, such as lymph nodes, and examining the cells under a microscope. This allows for the identification of characteristic malignant lymphoid cells that are indicative of lymphoma. A cytological examination can reveal changes associated with neoplastic lymphocytes, enabling veterinarians to make a more definitive diagnosis.

In contrast, urinalysis, hematocrit, and complete blood count may provide supportive information regarding a patient's overall health or help rule out other conditions, but they cannot specifically diagnose lymphoma. Urinalysis primarily evaluates the urinary tract, while hematocrit measures the proportion of red blood cells in the blood, and a complete blood count assesses various blood components but does not provide the cellular detail required to confirm lymphoid malignancies. Thus, cytology stands out as the most informative and definitive test for diagnosing lymphoma in small animals.