In this VETgirl podcast, we review the diagnostic yield of cytologic analysis of pericardial effusion in dogs. Is it worth submitting fluid analysis and cytology for your hemorrhagic sample? The most common causes of canine pericardial effusion include neoplasia and idiopathic effusions. Coagulopathies, left atrial rupture, and septic pericarditis are much less common. Among neoplastic causes, cardiac hemangiosarcoma (typically right atrial or right AV groove) occurs most frequently followed by heart base tumors (chemodectomas), mesothelioma, and lymphoma. Prognosis for neoplastic causes is highly dependent on tumor type. Cytologic analysis is considered highly useful in providing a definitive diagnosis of infectious causes and cardiac lymphoma, but is of limited value in identifying other neoplastic causes. This is in contrast to the relatively high diagnostic ability of pericardial effusion cytology to identify neoplastic etiologies in humans (likely because of the types of neoplasia seen in humans). Additional testing of blood or pericardial parameters/biomarkers (pH, lactate, glucose, bicarbonate, chloride, HCT, urea nitrogen) in dogs has proved to be of minimal additional diagnostic value. The main objective of this study were to quantify the ability of pericardial effusion cytology to provide a definitive etiology in dogs, with and without additional diagnostic data at time of presentation. In this podcast, we review the recent findings of a study by Cagle et al out of UC Davis. They retrospectively evaluated 259 dogs with cytology samples based off an electronic medical records review between 1990-2012. What they found? Depressing. Over 90% of the samples were considered nondiagnostic (in other words, hemorrhage!), while only 7.7% were found to be diagnostic. This study provides solid evidence-based parameters that can be used as guidelines for deciding whether to submit pericardial effusions for additional testing for patients, in particular when pet owners are financially constrained and further diagnostics must be prioritized (in which case the low relative overall diagnostic yield of effusion cytology may preclude necessity for its submission). VETgirl's philosophy? Echocardiography still remains the #1 diagnostic test to evaluate for causes of pericardial effusion and is the first diagnostic test recommended for such cases. What they did find in this study was that pericardial effusion RBC count and calculated HCT were significantly lower in diagnostic effusions. In particular, an effusion RBC count of 1.35 M/uL and a hematocrit value of 10% provided the ideal statistical cutoffs for nondiagnostic vs diagnostic effusions. Diagnostic utility of effusion cytology increased to 20.3% when effusion HCT was < 10%. So, what do we learn from this? Check a PCV off your pericardial effusion sample before submitting it for analysis. After all, it's cheap and easy to do, and every veterinary clinic can check a PCV (if they can't, boo!). Effusion PCV < 12-13% indicates greater potential diagnostic yield of adding cytologic analysis. Suggested reading: 1. Olcott MD, Sleeper MM. Recognizing and treating pericardial disease. Veterinary Medicine 2010. 2. Cagle LA, Epstein SE, Owens SD, et al. Diagnostic yield of cytologic analysis of pericardial effusion in dogs. J Vet Intern Med 2014;28(1):66-71. 3. Fine DM. Use of pericardial fluid pH to distinguish between idiopathic and neoplastic effusions. J. Vet. Intern. Med. 17 (4):525-529; 2003.