Incidental Identification of Plasmodium vivax During Routine Complete Blood Count Analysis Using the UniCel DxH 800

Dear Editor, A complete blood count (CBC) is one of the most frequently requested diagnostic tests in medical laboratories. This test is indicated, among others, for febrile patients who may be infected with malaria [1]. Currently available automated hematology analyzers are not designed to detect malaria-related signals. The incorporation of a ‘malaria flag’ into modern analyzers would allow for the development of an automated and adjuvant diagnostic tool for febrile patients who may have malaria, especially for patients with low pre-test expectation of the disease in non-endemic regions. Regarding the unexpected detection of malaria during CBC analysis, we describe the case of a 21-year-old male who visited the Daejeon St. Mary’s Hospital (Daejeon, Korea) with a persistent fever lasting 10 days and a pain in the left flank for two days at the time of diagnosis. The patient provided written informed consent for clinical analyses, and the study protocol was approv ed by the Institutional Review Board of the Catholic University of Korea. Physical examination revealed tertian fever of up to 40°C with chills and rigors, a pulse rate of 90 bpm, and a blood pressure of 110/60 mmHg. The laboratory findings were as follows: white blood cell count, 4.1×10/L; hemoglobin, 125 g/L; platelet count, 53×10/L; high-sensitivity C-reactive protein, 178.2 mg/ L; AST, 67 IU/L; ALT, 49 IU/L; lactate dehydrogenase, 884 IU/L; and creatine phosphokinase, 812 IU/L. Antigen and antibody tests for hepatitis B, C, and human immunodeficiency virus were negative. No pathogenic bacteria were identified in routine bacterial culture in blood, stool, and random urine samples. Thus, the patient was presumptively diagnosed as having severe fever with thrombocytopenia syndrome (SFTS) based on the low risk of malaria in his residential area (Ganam-eup, Yeojusi, Gyeonggi-do) and his recent travel to Jeju island, which is a major endemic area of SFTS in southern Korea [2]. However, routine CBC analysis using the UniCel DxH 800 (Beckman Coulter, Inc., Miami, FL, USA) lead to an “nRBC flag” warning with abnormal levels of nucleated RBC (nRBC; 4.43% and 182×10/L) in the WBC differential. In addition, low rotated low angle light scatter (RLALS)/low axial light (AL2)/low rotated upper median angle light scatter (RUMALS) in the nRBC plot showed unusual signals with characteristic, aggregated, round to upright, spindle-shaped cells, similar to those described in a previous report [3] (Fig. 1A and 1B). The patient was initially treated by oral administration of 800 mg of hydroxychloroquine as a loading dose. This was followed by 400 mg at 6, 24, and 48 hours after the