[Thrombocytopenia in horses].

OBJECTIVE: The retrospective study aimed to evaluate the prevalence of true thrombocytopenia and ethylenediaminetetraacetic acid (EDTA)-induced pseudothrombocytopenia in horses and ponies and to assess the diagnostic and prognostic utility of true thrombocytopenia.

MATERIAL AND METHODS: In 3592 patients (2008-2015) hematological data (ADVIA® 2120, Siemens) were reviewed. Inclusion criteria were platelet counts < 90 x 109/l (EDTA-blood) and/or < 84 x 109/l (citrate blood). Thrombocytopenia was classified as true, EDTA-induced, and questionable. Patients with true thrombocytopenia were assigned to nine groups according to their history and four groups depending on the main diagnosis (inflammatory disorders, neoplasia, non-inflammatory intestinal disease, others). The frequencies of diagnoses were compared to the overall clinic population.

RESULTS: Thrombocytopenia was diagnosed in 123/3592 patients (3.4 %) and classified as true in 60/123 (49 %), EDTA-induced in 6/123 (5 %), and questionable in 57/123 (46 %) of cases. In true thrombocytopenia, the most common reasons for referral were lethargy (23/60, 38 %), fever (19/60, 32 %), and colic (17/60, 28 %). In these patients inflammation, neoplasia, non-inflammatory intestinal disease, and others were diagnosed in 25/60 (42 %), 11/60 (18 %), 10/60 (17 %), and 14/60 (23 %) of cases, respectively. Compared with the overall clinic population, there was an increased frequency of neoplasia (18 % versus 1 %). The mortality rate was significantly higher at 38 % in comparison with the overall population. Remarkably high mortality rates of 32 % and 82 % were observed in patients with inflammatory and neoplastic diseases, respectively.

CONCLUSION AND CLINICAL RELEVANCE: True thrombocytopenia is relatively rare in horses with internal medical conditions and should be verified by measurement in samples with citrate as anticoagulant. Thrombocytopenia is rarely the primary reason for referral and is a negative prognostic factor in neoplastic and inflammatory diseases.