Platelet satellitism and platelet clumping can cause pseudo-thrombocytopenia. Platelet satellitism was first reported in the early 1960's. It is a rare condition that occurs when an IgG antibody forms 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 blood cells (WBCs) will not be counted as platelets by automated equipment and the platelet count will be falsely decreased. If a peripheral blood smear is reviewed, platelets will be observed attached to WBCs. The image on the right illustrates platelet satellitism with platelets adhering to a neutrophil.
Platelet clumping can also occur in the presence of EDTA and the platelet count again will be falsely decreased. The count will probably be flagged by the analyzer for platelet clumps or giant platelets.
If either platelet satellitism or platelet clumping is 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.