Use of the D‐dimer assay for diagnosing thrombosis in cases of canine cutaneous vasculitis

The objectives of this study were to measure D‐dimer concentrations and assess their value in diagnosis of thrombosis in three groups of dogs; (i) dogs with cutaneous vasculitis without histopathological evidence of thrombosis; (ii) dogs with cutaneous vasculitis with histopathological evidence of thrombosis; and (iii) pruritic dogs with erythematous skin and underlying allergic skin disease. D‐dimer test results were reported as negative at <250 ng/mL, and positive at ≥250 ng/mL. Ten dogs with a diagnosis of atopic dermatitis and/or cutaneous adverse food reaction were enrolled in the study, and the D‐dimer results were <250 ng/mL (eight dogs) and 250–500 ng/mL (two dogs). Twenty‐six dogs with a diagnosis of cutaneous vasculitis had blood samples submitted for D‐dimer analysis at the time of the initial submission of skin biopsies and results were: 15 had cutaneous vessel thrombi present with a D‐dimer of >500–1000 ng/mL (14 dogs) and >1000 ng/mL (one dog); 11 dogs had no histological evidence of thrombi with a D‐dimer of <250 ng/mL (four dogs), 250–500 ng/mL (three dogs) and >500–1000 ng/mL (four dogs). However, two of four dogs with a D‐dimer of >500–1000 ng/mL without histological evidence of thrombi developed necrotic skin lesions over the next 24–48 h. In conclusion, a D‐dimer >500 ng/mL is strong evidence to support the current presence or subsequent development of cutaneous vessel thrombosis, and a D‐dimer of <500 ng/mL correlates well with the absence of cutaneous vessel thrombi and necrotic skin lesions. No dogs with histopathological evidence of thrombi had a false‐negative D‐dimer.