False-Positive Nonstructural Protein 1 Antigen in a Patient with Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia: A Case Report with Literature Review.

BACKGROUND A rapid investigation of dengue viral infection is needed for physicians who manage patients with suspected dengue infection. The nonstructural protein 1 (NS1) test kit is commonly used to diagnose patients with acute febrile illness in dengue-endemic countries, although this test kit can yield false-positive results. The Dengue NS1 test kit mostly relies on cross-reaction among febrile illness patients with other viral infections rather than malignancies. CASE REPORT A 52-year-old male patient presented with 3 days of fever, intermittent gum bleeding, weight loss, and mucocutaneous bleeding. He was transferred to a second hospital with acute febrile illness. Both dengue NS1 antigen test kits were positive from the 2 hospitals where he was previously treated. Fever and cytopenia persisted, and then the dengue RT-PCR test was performed to establish the cause of illness. A peripheral blood smear was reviewed and showed blast cells. A bone marrow examination was done to test for the compatibility of lymphoblastic leukemia. The flow cytometry test showed B cells ALL with Philadelphia-positive chromosome. Finally, the result of the dengue RT-PCR test was negative. CONCLUSIONS Our patient presented with fever and viral-like illness, but he was finally diagnosed with Ph+ ALL. We demonstrated the first case of false-positive dengue NS1 antigen in a Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) patient. Moreover, we reviewed the literature to gather information on false-positive results using the dengue NS1 test kit. The dengue NS1 test kit is useful and produces reliable clinical findings, especially in patients with hematological malignancies.