Detection of platelet-bound and serum platelet-bindable antibodies for diagnosis of idiopathic thrombocytopenic purpura in dogs

David C. Lewis From the Department of Veterinary Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6520 (Lewis, Meyers); Section of Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010 (Callan, Giger); and the Department of Medicine, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536 (Bucheler).

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Kenneth M. Meyers From the Department of Veterinary Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6520 (Lewis, Meyers); Section of Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010 (Callan, Giger); and the Department of Medicine, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536 (Bucheler).

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M. Beth Callan From the Department of Veterinary Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6520 (Lewis, Meyers); Section of Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010 (Callan, Giger); and the Department of Medicine, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536 (Bucheler).

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Jörg Bücheler From the Department of Veterinary Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6520 (Lewis, Meyers); Section of Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010 (Callan, Giger); and the Department of Medicine, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536 (Bucheler).

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Urs Giger From the Department of Veterinary Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6520 (Lewis, Meyers); Section of Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010 (Callan, Giger); and the Department of Medicine, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536 (Bucheler).

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Summary

The sensitivity and specificity of 2 antibody tests for diagnosis of idiopathic thrombocytopenic purpura (itp) in dogs were investigated prospectively. An elisa to detect antibodies bound to the surface of platelets from affected dogs (direct test) was performed in 34 dogs with a clinical diagnosis of itp and in 21 dogs with thrombocytopenia attributable to other causes. An elisa to detect platelet-bindable antibodies in serum from affected dogs (indirect test) was performed in 32 dogs with itp and in 15 dogs with other causes of thrombocytopenia. The direct test was positive in 32 of 34 dogs with itp (sensitivity, 94%) and negative in 13 of 21 dogs with other causes of thrombocytopenia (specificity, 62%). Positive direct test results were obtained in 2 dogs with systemic lupus erythematosus, and in 1 dog each with concurrent Ehrlichia canis and Babesia canis infections, dirofilariasis, myelodysplasia, disseminated intravascular coagulation (of unknown cause), and thrombocytopenia subsequent to administration of trimethoprim/sulfadiazine, as well as in 1 dog with thrombocytopenia 14 days after a whole blood transfusion. The indirect test had positive results in 11 of 32 dogs with itp (sensitivity, 34%) and negative results in 12 of 15 dogs with other causes of thrombocytopenia (specificity, 80%). Positive indirect test results were obtained in 1 dog each with systemic lupus erythematosus, concurrent E canis and B canis infections, and thrombocytopenia subsequent to administration of trimethoprim/sulfadiazine. Detection of platelet-bound antibodies was more sensitive than detection of serumplatelet bindable antibodies in confirming a diagnosis of itp in dogs. Neither test was specific for itp. Therefore, a negative test result for platelet-bound antibodies in dogs with thrombocytopenia is helpful in excluding itp as a cause of thrombocytopenia; however, a positive test result is not specific for itp, and other causes of immune-mediated thrombocytopenia must be excluded to establish a diagnosis of itp.

Summary

The sensitivity and specificity of 2 antibody tests for diagnosis of idiopathic thrombocytopenic purpura (itp) in dogs were investigated prospectively. An elisa to detect antibodies bound to the surface of platelets from affected dogs (direct test) was performed in 34 dogs with a clinical diagnosis of itp and in 21 dogs with thrombocytopenia attributable to other causes. An elisa to detect platelet-bindable antibodies in serum from affected dogs (indirect test) was performed in 32 dogs with itp and in 15 dogs with other causes of thrombocytopenia. The direct test was positive in 32 of 34 dogs with itp (sensitivity, 94%) and negative in 13 of 21 dogs with other causes of thrombocytopenia (specificity, 62%). Positive direct test results were obtained in 2 dogs with systemic lupus erythematosus, and in 1 dog each with concurrent Ehrlichia canis and Babesia canis infections, dirofilariasis, myelodysplasia, disseminated intravascular coagulation (of unknown cause), and thrombocytopenia subsequent to administration of trimethoprim/sulfadiazine, as well as in 1 dog with thrombocytopenia 14 days after a whole blood transfusion. The indirect test had positive results in 11 of 32 dogs with itp (sensitivity, 34%) and negative results in 12 of 15 dogs with other causes of thrombocytopenia (specificity, 80%). Positive indirect test results were obtained in 1 dog each with systemic lupus erythematosus, concurrent E canis and B canis infections, and thrombocytopenia subsequent to administration of trimethoprim/sulfadiazine. Detection of platelet-bound antibodies was more sensitive than detection of serumplatelet bindable antibodies in confirming a diagnosis of itp in dogs. Neither test was specific for itp. Therefore, a negative test result for platelet-bound antibodies in dogs with thrombocytopenia is helpful in excluding itp as a cause of thrombocytopenia; however, a positive test result is not specific for itp, and other causes of immune-mediated thrombocytopenia must be excluded to establish a diagnosis of itp.

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