P543 Point-of-care testing in therapeutic drug monitoring of infliximab
Šahinović, I.(1);Orsic Fric, V.(2);Konjik, V.(3);Pavela, J.(4);Borzan, V.(5);Šerić, V.(1);
(1)University Hospital Osijek, Clinical department for laboratory diagnostics- University Hospital Osijek- Faculty of Medicine- J.J. Strossmayer University of Osijek, Osijek, Croatia;(2)University Hospital Osijek, Department of Gastroenterology- Clinic of Internal Medicine- University Hospital Osijek- Faculty of Medicine- J.J. Strossmayer University of Osijek, Osijek, Croatia;(3)University Hospital Osijek, Department of Pediatric Gastroenterology- Clinic of Pediatrics- University Hospital Osijek, Osijek, Croatia;(4)University Hospital Osijek, Clinical Department for Laboratory Diagnostics- University Hospital Osijek, Osijek, Croatia;(5)University Hospital Osijek, Department of Gastroenterology- Clinic of Internal Medicine- University Hospital Osijek, Osijek, Croatia;
Background
Within the past 20 years infliximab (IFX), a monoclonal antibody targeting tumor necrosis factor-alpha, has become an established therapy for inducing and maintaining remission in inflammatory bowel disease (IBD). IFX therapeutic drug monitoring (TDM) using the point-of-care (POC) methods showed to be able to produce results fast enough to allow IFX dose adjustments before drug infusion. This study aimed to compare IFX quantification using two POC tests, Procise IFX (Procise Dx) and Quantum Blue Infliximab assay (Bühlmann Laboratories AG).
Methods
Serum samples from 22 IBD patients (M=64%) on IFX maintenance therapy were collected immediately before drug infusion. Capillary blood was also collected from 6 IBD patients by finger prick using whole blood pipettes (Procise Dx). Crohn’s disease (CD) was diagnosed in 12 patients and ulcerative colitis (UC) in 10 patients. For method comparison, a Passing Bablok regression was used and for qualitative comparison weighted kappa statistic was obtained after stratification of results by therapeutic range (<3 mg/l, ≥3 to 7 mg/L, and ≥7 mg/L).
Results
Both methods measured lower IFX concentrations in CD patients (4,95 (0,65 – 5,80) mg/L) than in UC patients (8,50 (4,80 – 12,20) mg/L). In two patients with confirmed IFX antibodies, both methods showed immeasurably low IFX concentrations. Passing Bablok regression analysis of IFX concentration in serum sample has showed a proportional deviation between two POC methods (y=0.416 (-0.654 to 1.279) + 0.753 (0.648 to 0.923)x). A good comparison has been observed for capillary blood measured using Procise IFX test and serum samples measured using Quantum Blue Infliximab assay (y=-2.732 (-4.315 to 1,867) + 1.263 (0.278 to 1.566)x), although IFX concentration was lower in capillary blood. Classification of results according to therapeutic interval showed good agreement for serum samples and serum and whole capillary blood measurements (κ=0.79 (0.59-0.999 and κ=0.80 (0.45-1.00), respectively).
Conclusion
Because of proportional differences, two POC tests can’t be used interchangeably for longitudinal TDM of IFX in IBD patients. There is a need for caution in the interpretation of IFX in whole blood, due to its possibly lower concentration.