Author’s reply: Comment on: Isolated thrombocytopenia in childhood: what if it is not immune thrombocytopenia?

Dear Sir,

In the original study on isolated thrombocytopenia in childhood,(1) pseudothrombocytopenia was not included. Two cases of pseudothrombocytopenia were detailed in a prior publication.(2) That said, Sriwijitalai and Wiwanitkit’s comments(3) are important, as they are about pre-analytical, technical issues rather than genuine pathology. Although the mechanism is not fully understood, the occurrence of pseudothrombocytopenia is most likely a multifactorial phenomenon in which pre-existing autoantibodies are allowed to agglutinate platelets in vitro during sample storage, in a time-, temperature-, anticoagulant- and disease-dependent process.(4) However, the condition can be readily identified by examination of the blood film (Fig. 1a). Switching to an alternative anticoagulant for sample collection, as suggested by Sriwijitalai and Wiwanitkit,(3) is one way of resolving the spurious results. However, in our experience, beating the time factor with a new sample and running the test immediately is equally efficacious. This simple method has recently been proposed as the first manoeuvre when dealing with pseudothrombocytopenia.(4)

We recently encountered a four-month-old boy whose automated full blood count showed isolated thrombocytopenia of 17 × 10⁹/L with no clinical signs of bleeding. Examination of the blood film revealed a striking absence of normal platelets on the whole film, while the remaining platelets appeared degranulated and scattered in small clumps (Fig. 1b). A suspicion was raised that the blood sample had been manipulated. The phlebotomist later admitted that a blood clot had been manually removed from the ethylenediaminetetraacetic acid container before the sample was dispatched to the laboratory.

Fig. 1

Photomicrographs of peripheral blood films show (a) typical platelet clumping (black arrow) in a case of pseudothrombocytopenia, probably due to exposure to ethylenediaminetetraacetic acid anticoagulant during storage; and (b) degranulated platelets (white arrows) with some appearing as small clumps (circled) in a four-month-old child (Wright’s, × 100).

Keeping up laboratory quality can be challenging, but the importance of a carefully examined peripheral blood film cannot be overemphasised, whether the thrombocytopenia is spurious or genuine.

Yours sincerely,