PATIENT-LED REMOTE INTRACAPILLARY PHARMACOKINETIC SAMPLING (FINGERPRICKS): VALIDATION AND ACCEPTABILITY FOR HOME THERAPEUTIC DRUG MONITORING IN PATIENTS WITH IBD IN THE COVID-19 PANDEMIC

ABSTRACT

Background During the first wave of the coronavirus (COVID-19) pandemic, restrictive public health measures including prolonged shielding, were recommended by the United Kingdom government for many patients with immune-mediated inflammatory disorders treated with immunosuppressive and biologic drugs. Low-volume intracapillary blood sampling can be undertaken by patients at home and returned by post and may ensure access to therapeutic drug monitoring (TDM) for all patients irrespective of shielding status. Methods We undertook a cross-sectional blood sampling methods comparison study to assess the clinical validity and acceptability to patients of low volume intracapillary testing for serum TDM enzyme-linked immunosorbent assays (ELISA) compared to conventional venepuncture. Sample types were compared using linear regression and fit-for-purpose equivalence was defined using total allowable error (TEa) rates derived using interassay coefficient of variations from routine clinical practice. Acceptability was assessed using a purpose-designed questionnaire. Results The median (IQR) volume of serum obtained using intracapillary sampling was 195μL (130 - 210). We showed drug level equivalence (slope [95% CI] TEa vs observed mean % difference) between intracapillary sampling and conventional venepuncture for adalimumab (1.02 [0.90 - 1.14] 11.7% vs 2.1%) (Figure 1), infliximab (1.08 [0.98 - 1.18] 18.3% vs 1.2%), vedolizumab (0.91 [0.85 - 0.96] 17.6% vs 4.1%), and ustekinumab (0.92 [0.90 - 0.94] 19.4% vs 3.3%). Anti-drug antibody equivalence was observed for antiadalimumab (0.96 [0.95 - 0.98] 24.5% vs 2.1%) and anti-infliximab (0.89 [0.81 - 0.97] 17.3% vs 1.3%) antibody levels. Most patients reported that intracapillary testing was easy, convenient, and that they preferred it to conventional venepuncture (Figure 2). Conclusions Low-volume intracapillary blood sampling was equivalent to conventional venepuncture for the measurement of biologic drug and anti-drug antibodies. Patients preferred intra-capillary testing to conventional venepuncture. Irrespective of future COVID-19 surges, patient-led intracapillary blood sampling is likely to become a key adjunct to telemedicine in patients with immune-mediated inflammatory diseases.(Figure Presented) Adalimumab drug Linear regression and Bland Altman plot Left Linear regression analysis of venous vs capillary adalimumab drug level results (mg/L), Slope 1.02 [0.90 - 1.14]. Right Bland Altman plot of mean of venous and capillary adalimumab drug measurement against percentage difference between TEa vs observed mean % difference.(Figure Presented) Figure 2 Questionnaire acceptability response data Patient acceptability questionnaire response results by 5-point Likert scale. (A) Itemised proportional responses, grouped by domain. (B) Cumulative agreement per respondent;+1/+2 points for agree/strongly agree, 0 for neither agree nor disagree, -1/-2 for disagree/strongly disagree. Lowest decile reflecting participants with lowest acceptability scores indicated.