EDTA (ethylenediaminetetraacetic acid) is a commonly used anticoagulant for venous blood samples. Pseudothrombocytopenia may occur in some patients due to EDTA-dependent platelet agglutination and/or satellitism about neutrophils.


Findings in EDTA-dependent pseudothrombocytopenia:

(1) low platelet count result from an automated platelet counting instrument

(2) clumps of platelets seen on peripheral blood smear, or platelets surrounding neutrophils

(3) the platelet estimate on the peripheral blood smear is significantly higher than the automated counting instrument value

(4) Occasionally a clinical history indicating no significant risk for a hematologic or coagulative disorder (no clinical explanation for thrombocytopenia).



(1) The patient's blood is redrawn in another anticoagulant such as sodium citrate.

(2) The sample is run through the automated platelet counting instrument and a peripheral blood smear is made.

(3) Because sodium citrate is a liquid which dilutes the blood sample slightly, the instrument's platelet count must be corrected for the citrate volume. This is done by multiplying the instrument's reading by a correction factor (1.1).



• If no platelet clumps or satellitism are seen on the peripheral blood smear using the citrated specimen, and if the platelet estimate on the peripheral blood smear using the citrated specimen roughly agrees with the automated platelet count on the same specimen, then EDTA-dependent pseudothrombocytopenia is presumed present.

• If platelet clumps or satellites are still seen, then sometimes an accurate platelet count can be made by performing a manual platelet count in a hemocytometer, using a non-EDTA anticoagulant.

• If the platelets clumps are still seen, the possibility of in vivo platelet aggregation due to a hypercoagulable state should be considered.


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