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Too many times in the hustle and bustle of today's clinical laboratories, we do not always think of relatively rare phenomena such as ethylenediaminetetraacetic (EDTA)-induced pseudothrombocytopenia. Upon encountering such a case recently, I began heavily researching the subject.
The case I encountered produced severe pseudothrombocytopenia. The patient was admitted to the emergency department and it was discovered that she had a subdural hematoma and was scheduled for immediate surgery.
Working Under Pressure
The pressure was on to get the results of her CBC STAT. The analyzer we were using did not flag platelet clumps, but due to the low platelet count, a slide was made to review the platelet morphology.
In the midst of the staining process, I answered the calls of frantic surgery staff members who were anxiously awaiting the results. Upon review of the slide, no platelet clumps were observed and very few platelets were seen on the smear.
The estimate appeared to agree with a 19,000/microliter platelet count. By the time the critical result was called, the patient was already in surgery. A repeat CBC was ordered later that night on another shift, yielding results of 17,000/microliter for the platelet count.
An order to transfuse a platelet pheresis unit was received in the blood bank and the unit was subsequently transfused.
The day-shift hematology technologist was familiar with the patient's history of EDTA platelet sensitivity and launched an investigation into the case of supposed thrombocytopenia the following day.
Upon meticulous review of the slides accompanying the two CBC samples, platelet clumps were observed; however, they only appeared at the very edges of the peripheral blood smears.
The technologist ordered a sodium citrate tube to be drawn and the platelet count was found to be within normal limits. The patient's name was added to the abnormal patient card file that I recently created for the hematology department.
When patients have a history of EDTA platelet sensitivity, it should be documented in their medical record, ranking in equal importance as drug allergies. In this patient's case, the unnecessary administration of blood products occurred and could have been avoided.
It is a common procedure to vortex samples exhibiting mild EDTA platelet sensitivity to disperse the clumps. It was in our procedure to vortex the samples for 1-2 minutes, immediately repeat the CBC and make a slide of the post-vortexed sample. In this patient's case, vortexing was not sufficient to disperse the clumps.
Dependent Antibodies
The exact mechanism is not entirely understood, but it is believed that platelet autoantibodies bind to the glycoprotein IIb epytope.1
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