ORIGINAL ARTICLE: Lack of association between elevated mean red cell volume and haematological toxicity in patients receiving long‐term methotrexate for rheumatoid arthritis

Aims: It has been suggested that elevated mean red cell volume (MCV) may be a predictor of haematological toxicity in rheumatoid arthritis (RA) patients receiving methotrexate (MTX). We wished to identify whether there was an association between MCV, red cell folate and haematological toxicity in patients on MTX monotherapy for the long‐term management of RA. Methods: Evidence of haematological toxicity was sought by note review of patients recruited in a cross‐sectional study of MTX monotherapy in RA. Retrospective data included MCVs from before MTX initiation and after 3 and 6 months of treatment. Data were collected prospectively every 6 months for up to 2 years after enrolment. Any record of cytopenia or the development of haematological malignancy was recorded from commencement of MTX until the present day. Red cell folate concentrations were tested on enrolment to the study. Results: A total of 165 patients was included, 74.5% female, median disease duration 7 years (range 3 months–57 years). The median duration of MTX treatment was 74.9 months (range 10–241 months) giving 1030.2 patient‐years of MTX exposure. Twenty‐four patients (14.5%) had a MCV > 98 fL on study entry. Evidence of haematological abnormality was found in six patients (3.6%); chronic lymphocytic leukaemia (1), persistent lymphocytosis (1), persistent monocytosis (1) and neutropenia (3). There was no association between red cell folate or MCV and haematological toxicity. Conclusion: Neutropenia and pancytopenia are rare side‐effects of MTX therapy in this cohort. Elevated MCV or low mean red cell folate does not appear to be associated with haematological malignancy or toxicity in this cohort of patients on long‐term MTX therapy.