Platelet Clumps in Citrate Tube

Dear Fritsma Factor,

I am a hematopathology fellow evaluating the following patient for thrombocytopenia. History and laboratory results are listed in detail below. We have encountered a situation where the patient develops platelet clumps within citrate tubes but not in EDTA. I have found only limited information regarding this phenomenon and was wondering if anyone has encountered this during their practice or has references relating to this problem. Thank you for your assistance.

The individual is an 8 year old boy with a history of intermittent thrombocytopenia initially occurring during hospitalizations at age 3–5 years for asthma exacerbation. Earlier this year he had a large bruise on his abdomen without trauma and was found to have thrombocytopenia with a platelet count of approximately 17K. A few months later he acquired a paper cut and subsequently developed prolonged bleeding from the lesion which awoke him from sleep and was running down his arm. His baseline platelet count has ranged from low normal  to mild thrombocytopenia 131–161K since 2014. He has had no major bleeding challenge. He denies epistaxis and bleeding of gums. He is scheduled for adenotonsillectomy due to obstructive sleep apnea.
During laboratory testing for PFA-100 and platelet aggregation, he was found to platelet clumping which only developed in the sodium citrate tube, but not in EDTA. This phenomenon has occurred on at least 3 visits. In EDTA the platelet count is approximately 130–140K but drops to 50–80K in citrate tubes with noted clumping. Laboratory testing for vWD is negative. Bleeding time is slightly elevated at 8.5 min. Whole blood platelet aggregation was performed with relatively normal patterns and mildly attenuated response to epinephrine compared to control.

Thank you for your time, Sincerely, Michelle Foshat, MD

Hello, Dr. Foshat, and thank you for this interesting case. Platelet satellitosis and clumping is an in vitro phenomenon most often seen in blood films made from EDTA tubes, perhaps caused by EDTA-mediated IgG autoantibodies directed against the platelet glycoprotein IIb/IIIa complex and the neutrophil Fc γ receptor. (Bobba RK, Doll DC. Platelet satellitism as a cause of spurious thrombocytopenia. Blood 2012;119:4100). I’ve seen at least one case in which satellitosis and clumping occurs both in the EDTA and the sodium citrate tube, but have not seen a case where it occurs only in the citrate tube. Since this phenomenon is only partially understood, I’d be inclined to say, “anthing can happen.” When satellitosis occurs in the EDTA tube it causes a spurious thrombocytopenia that create clinical concern if the characteristic blood film appearance goes unrecognized, however satellitosis appears to have no clear clinical associations.
In your patient’s case, it seems as though two mechanisms have been at work, both in vitro satellitosis and episodic thrombocytopenia. Presuming the platelet counts from the EDTA tubes are accurate, our clinical Fritsma Factor participants might speculate that he had experienced a self-resolving episode of acute immune thrombocytopenic purpura (AITP, Yildiz I, Ozdemir N, Celkan T, et al. Initial management of childhood acute immune thrombocytopenia: single-center experience of 32 years. Pediatr Hematol Oncol. 2015;32:406–14.) For his future management, including procedures, his clinicians will want to keep in mind the recurrence rate for childhood AITP is ~3%, and there are cases in which AITP may become chronic.