Optimising Blood Test Monitoring Frequency for Inflammatory Bowel Disease Patients: Balancing Adherence, Comfort and Risk.

Abstract

Background: Inflammatory bowel disease (IBD) therapies can cause myelosuppression and hepatitis. The European Crohn's and Colitis Organisation (ECCO) recommends 3-monthly blood test monitoring; however, these recommendations are largely based on expert consensus, and real-world evidence informing optimal long-term monitoring intervals remains limited.

Aim: To determine the incidence of medication-related hepatitis and myelosuppression in a population-based IBD cohort and estimate the laboratory monitoring burden required to detect clinically significant adverse events.

Methods: A retrospective cohort study was performed using the Manawatū IBD incidence cohort. Patients diagnosed with IBD between 1 January 2011 and 31 December 2015 were followed longitudinally until 31 December 2022. Medication exposure, laboratory results, and clinical outcomes were recorded. Hepatitis was defined as alanine aminotransferase (ALT) > 2 × the upper limit of normal, while myelosuppression was defined as a neutrophil count < 1.0 × 10⁹/L. Patients were followed from diagnosis until the first outcome event or last recorded follow-up. Medication exposure was analysed as a time-varying variable using cox proportional hazards regression, and the duration of laboratory monitoring required to detect one adverse event was calculated.

Results: Among 204 incident cases, 12 were excluded due to prediagnosis hepatitis or myelosuppression, leaving 192 patients for analysis. Twenty-four hepatitis events and two myelosuppression events were observed during 1739 patient-years of follow-up. 6-mercaptopurine (hazard ratio [HR] 39.2, p < 0.001), azathioprine (HR 6.26, p = 0.002), methotrexate (HR 9.94, p = 0.004) and lower mean corpuscular volume (HR 0.89, p = 0.001) were independently associated with hepatitis. Following the initial 6 months of therapy, one hepatitis event was detected for every 33 patient-years of stable thiopurine exposure monitored with routine quarterly blood testing.

Conclusion: Clinically significant hepatitis and myelosuppression were uncommon in this population-based IBD cohort, particularly after the initial 6 months of therapy. These findings suggest that reduced laboratory monitoring frequency in carefully selected patients with established treatment stability warrants evaluation.