Predictive Significance of Peripheral Blood Smears in Patients with Fever of Unknown Origin: A Retrospective Study of 2871 Cases

Fever of unknown origin (FUO) is a common manifestation and diagnostic problem especially in primary care. Pointing out a diagnosis of FUO often requires numerous noninvasive and invasive procedures. Peripheral blood (PB) smear examination frequently provides many timely and valuable diagnostic clues in various disorders. Few assessments of PB smear morphologic examinations used in the diagnostic evaluation of FUO have been reported.To determine whether PB smears have important roles in exploring the causes of FUO, we collected PB smears of 2871 FUO patients from Beijing Chao-yang Hospital affiliated to Capital Medical University from September 2012 to August 2014. Combined with relevant clinical data, we analyzed the PB morphologic features in all the FUO patients.We found the presence of atypical lymphocytes (64.33%), nuclear left shift (46.33%), toxic granulation, vacuolization, and 4 cases of malaria in FUO patients, markedly more than the health control group (p < 0.05), and morphologically consistent with the diagnosis of infectious diseases. Notably, the presence of blasts or immature cells in 26 cases (9%o) and the abnormal changes of leukocytes, erythrocytes or platelets in 4 cases provided predictive information for exploring the causes of FUO, followed by bone marrow smears and other procedures to further confirm the diagnosis as hematological diseases, including acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), Evans syndrome, agranulocytosis, immune thrombocytopenic purpura (ITP).Our findings demonstrate that a timely and careful observing of PB smears is helpful for clarifying the diagnosis and contributes to appropriate treatment in patients with FUO.