A prospective study of hospitalized patients with leukemoid reaction; causes, prognosis and value of manual peripheral smear review.

INTRODUCTION: Several diagnoses have been associated with leukemoid reaction (LR). In patients with LR the diagnostic and prognostic value of detailed manual blood smear counts (such as the percentage of band cells or grading of neutrophil toxic changes) has not been studied previously.

METHODS: We prospectively recorded all hospitalized adult (> 18 years old) patients with LR (≥ 30000/ul) of neutrophilic predominance, excluding patients with pre-existing leukocytosis due to hematological malignancies. We examined the diagnoses and prognosis (in-hospital mortality and post-discharge mortality up to a year after the end of the study) of these patients as well as the value of manual peripheral smear review.

RESULTS: We recorded a total of 93 patients with LR from January 2017 to December 2017. Infection was the most common diagnosis (70%), followed by malignancy (7.5%) and bleeding (6.5%). In-hospital mortality (45%) and post-discharge mortality (35% of those discharged) were very high. Among blood smear findings, only neutrophil vacuolation was significantly more common in patients with infections (34%), although it was also observed in many patients without any infection (13%). Blood smear findings were not associated with prognosis.

CONCLUSION: Detailed manual smear review is a labor-intensive procedure and it has limited diagnostic and prognostic value in unselected hospitalized patients with neutrophilic LR.