Platelet satellitism and platelet clumping can cause pseudo-thrombocytopenia. Platelet satellitism is a rare occurrence that is the result of an IgG plasma antibody coating platelets in the presence of EDTA, the anticoagulant that is used for the collection of hematology blood specimens. The IgG antibody is directed against the glycoprotein IIb/IIIa complex on the platelet membrane. 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 will be observed attached to white blood cells. 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 the sample is collected.
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. The platelet count will typically be flagged by an automated hematology analyzer for platelet 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 that contains liquid sodium citrate will need to be corrected for the dilutional effect of the citrate; this can be accomplished by multiplying the platelet count that is obtained from the automated analyzer by 1.1.
