**5.5 A pericardial fluid analysis**

Pericardial effusion cytology is believed by many to be of limited value, yet few studies have evaluated its diagnostic utility. Cytologic analysis of pericardial effusion provides an accurate and definitive diagnosis when infectious agents or lymphoma are the causative aetiologies. Conversely, neoplastic diagnoses other than lymphoma (hemangiosarcoma, chemodectoma, mesothelioma) are rarely diagnosed based on cytology alone, and additional diagnostic tests performed on fluid or blood samples have a poor ability to distinguish these from non-neoplastic aetiologies (**Table 1**).

The effusion typically has a haemorrhagic appearance (port wine in colour) despite the underlying cause. Fluid analysis may be diagnostic in cases of infection or lymphosarcoma; therefore, although cytologic evaluation has a low diagnostic yield, it is still recommended [11].
