Platelet satellitism and platelet clumping can cause pseudo-thrombocytopenia. Platelet satellitism is a rare occurrence resulting from an IgG plasma antibody coating platelets in the presence of EDTA. This anticoagulant is used for the collection of hematology blood specimens. The IgG antibody is directed against the platelet membrane's glycoprotein IIb/IIIa complex. As the antibody coats the platelets, the platelets rosette around segmented neutrophils, bands, and sometimes around monocytes. Antibody-coated platelets that are huddled around white cells will not be counted as platelets by automated hematology analyzers, and, therefore, the platelet count will be falsely decreased. If a peripheral blood smear is reviewed, platelets attached to white blood cells will be observed. The top image on the right illustrates platelet satellitism with platelets adhering to a neutrophil. Satelliting is optimum at room temperature (18 - 22°C) and peaks approximately 60 minutes after collecting the sample.
Platelet clumping (as shown in the bottom image on the right) can also occur in the presence of EDTA, leading to a falsely decreased platelet count. An automated hematology analyzer will typically flag the platelet count for clumps or giant platelets.
If either platelet satellitism or platelet clumps are observed on the peripheral smear, the sample could be recollected using sodium citrate as the anticoagulant. Platelets can then be counted using the automated method. The platelet count from a tube containing liquid sodium citrate will need to be corrected for the dilutional effect of the citrate; this can be accomplished by multiplying the platelet count obtained from the automated analyzer by 1.1.
