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In Singapore and countries with similar demographics, hereditary thrombophilia screening should be confined to testing for protein C, protein S and antithrombin III.

An 80-year-old woman presented at the Emergency Department with a complaint of persistent cough of 1 week's duration. Her full blood count (FBC) at consultation showed a white cell count (WBC) of 27AE1 · 10 9 /l, a haemoglobin concentration of 136 g/l and a platelet count of 280 · 10 9 /l. A blood film was made due to morphology flags for monocytosis and lymphocytosis. Upon review of the blood film, it was noted that there were numerous nucleated red blood cells (RBCs) and neutrophilia with a mild left shift (left). Closer scrutiny revealed that these 'nucleated RBCs' were atypical in shape with cytoplasm similar in colour to normal RBCs. The nuclei of these atypical cells showed heterochromatin but were of a different colour compared to human nucleated RBCs. The morphology of these 'nucleated RBCs' resembled that of avian RBCs. Avian red cells are nucleated and are described as ellipsoid with eosinophilic cytoplasm; the nucleus varies from round to slight ellipsoid with irregularly clumped chromatin. Therefore, we conjectured that the patient's specimen was contaminated by 'carryover' from a control sample.Our investigations showed that the patient's blood specimen was the first specimen analysed after a routine internal quality control check for reticulocytes, which was performed in a capped automated mode. We used the Coulter Retic-C TM Cell Control on a Coulter LH 750 Hematology Analyzer.The control is a mixture of human and avian RBCs. A check of the most recent preventive maintenance report showed an acceptable carryover rate of 1AE6% (acceptable limit 2%). A repeat of the carryover test performed immediately after this incident once again showed an acceptable carryover rate of <2%. A smear of the Level III (high level) Coulter Retic-C TM Cell Control (right) showed an abundance of cells with a similar morphology. Thus, even though the carryover test is acceptable, it did not eliminate the possibility of contamination of patient's specimen by control material. Further investigations revealed that, for that particular run of the Retic-C TM Cell Control, the manufacturer's recommended order of running the controls from Level III to I (highest to lowest reticulocyte percentage) was not followed. The recommended running of a prime blood sample prior to the analysis of patient samples was also not adhered to. These further steps would have further reduced the carryover possibility. Following this incident, the need to follow correct laboratory procedures to avoid unacceptable errors due to carryover from control samples was emphasized, as was the need for additional cleaning cycles to the sampling tip after analysis of samples with a high white cell count.

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