P761: MONOCYTOSIS IN PRIMARY CARE AND HEMATOLOGICAL MALIGNANCIES

Abstract

Background: Monocytosis (blood monocyte count > 0.8 x109/L) is relatively often observed in routine blood work from primary care, however, the significance is not always apparent as monocytosis may be present in a spectrum of diseases spanning from mild infections to chronic myelomonocytic leukemia. Aims: We aimed to examine the predictive value of monocytosis in primary care by relating monocyte count to subsequent 3-year incidence of hematological malignancy. Methods: We included 663.184 adult patients from primary care in the greater Copenhagen Area who had a complete blood cell count (CBC) performed at any time between 2000-2016. For patients with multiple samples registered, a random sample was selected and samples predating the index CBC by 3 months were assessed to account for sustained monocytosis. Using the extensive Danish health data registers, we collected data on incident hematological malignancy for 3 years following the CBC. We modelled the association between monocyte count and hematological malignancies as well as all-cause mortality using multiple logistic regression analysis. Results: Monocytosis was observed in 4,6 % of CBCs. We saw an increased risk of myeloid malignancies with the most noticeable being an odds ratio (OR) for CMML > 100 with monocytosis > 1.0 x 109/L. Sustained monocytosis increased this risk to OR >140. The incidence was, however, still low with only 0.1% of patients with monocytosis developing CMML within 3 years. Risk of lymphoproliferative and M-component related diseases were also increased, however, other relevant cell line were affected as well in these cases. Summary/Conclusion: Monocytosis is a common finding in primary care, but even with monocytosis > 1 x 109/L hematological malignancies are rare. Optimized referral to secondary care remains a challenge and if the clinical presentation leaves doubt of the diagnosis, repeated measurements help demask if malignancy is the cause of the monocytosis.