Anaemia, ethnicity and cancer incidence: a retrospective cohort study in primary care.

Background Haemoglobin, Mean Corpuscular Volume (MCV), and rates of Iron Deficiency Anaemia (IDA) are used in primary care to investigate possible cancer symptoms, especially for gastro-intestinal cancers. Underlying ethnic differences in typical test results could lead to inequalities in the diagnosis of cancer in primary care. Aim To investigate the distribution of low haemoglobin, low MCV and IDA, and the rate of cancer diagnosis in patients with abnormal results, by ethnic group. Design and Setting Retrospective cohort study using routine data collected in primary care in England. Included patients had blood tests between 2010 and 2017 and were at least 40 years old with no prior cancer diagnosis. Method Multi-level logistic regression was used to investigate the relationship between blood test results and cancer risk for patients in different ethnic groups. Results Low haemoglobin, low MCV, and IDA were effective in identifying patients with increased cancer risk, particularly for gastro-intestinal cancers. MCV was found to be a stronger cancer indicator for White patients (diagnostic OR 3.84) than for Asian (OR 1.86) or Black patients (OR 1.75). Conclusion There are some small differences in cancer risk for patients with abnormal test results, when considering patient ethnic group, especially for MCV. This is likely to be a consequence of the underlying difference in typical MCV values for patients from different ethnic groups. Further investigation is required to understand the aetiology of these differences in order to disentangle any effects on outcomes for patients with cancer.