Pseudo-reticulocytosis as a result of malaria parasites

Recently fully automated methods for enumerating reticulocytes have become available as an integral function in routine haematology analysers. In such methods, all intraerythrocytic nucleic acid is stained and can be regarded as representing reticulocytes. It has previously been shown that Howell-Jolly bodies may be counted as reticulocytes in automated flow cytometric methods. In the present paper, data from two patients are described indicating that severe malaria infection may lead to falsely increased reticulocyte counts, at least in the CELL-DYN (R) 4000 haematology analyser. In this instrument, the intraerythrocytic nuclear material of the parasites will be stained and counted as reticulocytes. This phenomenon appears to be independent of the type of Plasmodium infection. Clinical haematology laboratories should be aware of this potential source of pseudo-reticulocytosis.