EDTA-induced platelet aggregation can be avoided by a new anticoagulant also suitable for automated complete blood count.

In vitro EDTA-induced platelet aggregation is a fairly rare event but can have serious clinical consequences producing pseudothrombocytopenia and pseudoleukocytosis. Sixteen specimens with previously recognized EDTA-induced platelet aggregation were collected in a new anticoagulant-antiaggregant mixture containing trisodium citrate 17 mmol/l, pyridoxal 5'-phosphate 11.3 mmol/l and Tris 24.76 mmol/l (CPT mixture) and analyzed at various times after venepuncture with four hematological instruments: Coulter Counter S-Plus STKR, Technicon H6000, Technicon H1 and Ortho ELT-8. In CPT-anticoagulated specimens the signals and instrumental flags of platelet clumping were absent, and the platelet number correlated very well with a microscopic count from a finger stick drawn into Unopette. The complete blood count was very similar in "normal" hematological specimens either collected in K3. EDTA or in CPT, although Technicon H1 and Ortho3 ELT-8 required a suitable calibration for MCV and hematocrit in the latter mixture. Mean platelet volume was stable for up to 24 h only in CPT-collected specimens, if it was measured on a Coulter Counter S-Plus STKR. In routine hematological practice CPT can be an alternative anticoagulant to K3. EDTA, most suitable for automated complete blood count and useful in avoiding EDTA-induced platelet clumping.