A combination of clinical and laboratory markers can be used as a tool to differentiate between primary and secondary immune thrombocytopenia in dogs.

Objective: To evaluate the discriminatory potential of selected clinical and routine laboratory markers to differentiate primary immune thrombocytopenia (pITP) and secondary immune thrombocytopenia (sITP) in dogs.

Methods: A retrospective diagnostic accuracy study including dogs with severe immune thrombocytopenia (platelet count [PLT] < 50 X 109/L) presenting between 2014 and 2024 to a single university veterinary hospital, which were identified by laboratory database search and subsequent review of medical records.

Results: The study included 17 dogs with pITP and 36 with sITP. Dogs with pITP had significantly lower PLT (median, 8 X 109/L [IQR, 3 to 21]) and C-reactive protein (CRP; median, 20.5 mg/L [IQR, 6.4 to 76.6]) compared to dogs with sITP (PLT median, 25 X 109/L [IQR, 13 to 35] and CRP median, 72.7 mg/L [IQR, 37.3 to 137.3]) and were significantly more likely to present with bleeding diathesis. The combination of bleeding diathesis, PLT < 8.5 X 109/L, and CRP < 25 mg/L had a positive likelihood ratio of 8.8 for pITP.

Conclusions: The combination of bleeding diathesis, PLT, and CRP concentration shows potential for differentiating between dogs with pITP and sITP.

Clinical relevance: Differentiating between pITP and sITP is imperative, as treatment is widely different. The results of the current study could potentially be used to help guide clinical decision-making.