Psuedothrombocytopenia - A caveat

Pseudothrombocytopenia is an ex vivo thrombocytopenia, counted by an automated cell counter, but not configured by microscopic examination of a well prepared blood smear. Incidences of pseudothrombocytopenia reported in different studies range from 0.09-0.21%, which could account for 15-30% of all cases of thrombocytopenia. Failure to identify pseudothrombocytopenia has led to a lot of clinical problems like unnecessary platelet transfusion, glucocorticoid therapy and so on. Haematological cell counters count platelets as particles with volume between 2 and 20fl. Thus platelet clumps are counted as leucocytes while fragmented RBCs as platelets. This study found pseudothrombocytopenia due to causes like EDTA blood stored at less than 32oC for more than 2 hours (35%), excess EDTA in sample (10.7%), hyperlipidaemia, auto-immune disease, pregnancy, etc. No apparent cause could be found in 52% of cases. Hence it is emphasised that direct microscopic examination of a well stained blood smear from EDTA-venous blood (within 1hour) and or direct counting under Neubauer chamber with 1% ammonium oxalate (in special cases) is almost mandatory before releasing a report of platelet count. Also factors related to ratio and storage of EDTA-blood, calibration of instruments, proper selection of reagents, supervision of laboratory staff are essential to rule out any error of report including pseudothrombocytopenia.