Microcytosis as a risk marker of cancer in primary care: a cohort study using electronic patient records

Abstract

Background: Microcytosis, smaller than normal red blood cells, has previously been identified as a possible early risk marker for some cancers. The role of microcytosis across all cancers has not been fully investigated. Aim: To examine cancer incidence in a cohort of patients with microcytosis, with or without accompanying anaemia Design and setting: Cohort study of patients aged ≥40 years using UK primary care electronic patient records. Methods: The 1-year cancer incidence was compared between cohorts of patients with a mean red cell volume of < 85fL (low) or 85fL-101fL (normal). Further analyses examined gender, age-group and cancer site, and haemoglobin values. Results: 497 out of 12,289 patients with microcytosis had a new cancer diagnosis within 1 year (4.0%, 95% confidence interval 3.7 to 4.4), compared to 1,465 of 73,150 without microcytosis (2.0%, CI 1.9 to 2.1). In males, 298 out of 4,800 with microcytosis developed cancer (6.2%, CI 5.5 to 6.9), compared to 940 out of 34,653 without (2.7%, CI 2.5 to 2.9). In females with microcytosis, 199 out of 7,489 developed cancer (2.7%, CI 2.3 to 3.1), compared to 525 out of 38,497 without (1.4%, CI 1.3 to 1.5). In patients with microcytosis but normal haemoglobin, 86 out of 2,637 males (3.3%, CI 2.6 to 4.0) and 101 out of 5,055 females (2.0%, CI 1.6 to 2.4) were diagnosed with cancer. Conclusions: Microcytosis is a predictor of underlying cancer even if haemoglobin is normal. Although a benign explanation is more likely, clinicians in primary care should consider simple testing for cancer in unexplained microcytosis, particularly in males.