Thrombocytopenia is a well-documented adverse reaction of sunitinib. Thrombocytopenia was observed in a patient with metastatic renal clear-cell carcinoma undergoing sunitinib treatment. Platelet count in an ethylenediaminetetraacetic acid (EDTA) sample was 19 × 109/l. To exclude pseudothrombocytopenia (PTCP), a platelet count in citrate-anticoagulated blood was performed, showing a platelet count of 6 × 109/l. Due to the apparent thrombocytopenia, the patient received platelet concentrates. Subsequent analyses revealed PTCP whereby platelet clumping was most abundant in citrate-followed by EDTA- and heparin-anticoagulated blood samples. This effect was partially reversed after placing blood samples at 37°C. The IgM antiplatelet autoantibodies responsible for in vitro agglutination are temperature and multianticoagulant dependent and did not react to amikacin pre-supplementation. Remarkably, the antibody revealed specificity to platelet antigens other than GPIIb/IIIa, GPIb/IX, GPIa/IIa, GPIV, and GPV. After 16 days of discontinuing sunitinib, no PTCP and no platelet reactive antibodies could be detected. We report a case of PTCP with clear time-relation with sunitinib, strongly suggesting the mechanism to be sunitinib dependent. Since this finding has not been described before, non-recognition of PTCP during sunitinib treatment might lead to dose reduction or unwarranted therapy.

Platelet aggregation, Pseudothrombocytopenia, Sunitinib, Thrombocytopenia,
Platelets (London)
Department of Medical Oncology

Albersen, A, Porcelijn, L, Schilders, J, Zuetenhorst, H, Njo, T, & Hamberg, A.P. (2013). Sunitinib-associated pseudothrombocytopenia induced by IgM antibody. Platelets (London), 24(7), 566–570. doi:10.3109/09537104.2012.731545