Ulcerative colitis is a form of chronic inflammatory bowel disease which affects the mucous membrane of the gastrointestinal tract. The diagnosis of the disease is based on a multitude of tests and analyses of different parameters, including C-reactive protein in the blood and calprotectin in the faeces, which are markers of inflammation in the body. For the treatment of the disease, biological drugs, like ustekinumab, are being used more often. Ustekinumab is a human monoclonal antibody that binds to the subunit p40 of the interleukins 12 and 23 and blocks them binding to their receptors. Consequently, it also blocks the activation of cell signalization and the proinflammatory immune response. Hanžel and coworkers (2020) have discovered that concentrations of ustekinumab in a certain week of treatment can have a prognostic value for how the patient will respond to treatment.
The purpose of our assignment was to measure ustekinumab with two different ELISA analytical kits in 165 samples of serum of 12 patients with ulcerative colitis and determine their agreement and determine a connection between the concentrations of the drug and inflammation parameters (C-reactive protein, faecal calprotectin) with disease activity. We tested the agreement between kits statistically – Shapiro-Wilk test for the verification of normality of the data, Spearman test for assessment of correlation, we checked the linear regression with the Passing-Bablok regression and then performed the Bland-Altman test. We also calculated the intra- and inter-assay precision for the performed analyses and accuracy for one analysis. In certain patients samples we also checked for the presence of free and total anti-ustekinumab antibodies, which could interfere with treatment.
The statistical tests showed good agreement between the kits. We determined there was no connection between C-reactive protein and the drug concentrations in most patients. A better connection was seen between concentrations of faecal calprotectin and ustekinumab. We also compared ustekinumab concentrations with achieving biochemical remission (<100 mg/kg faecal calprotectin) in the 16th and 24th week of treatment – we could assume with both methods that patients, who have a ustekinumab concentration >40 μg/mL in the second week of treatment, have a bigger probability of achieving biochemical remission in the 16th week of treatment. Out of a total of 17 samples from 6 patients, only 6 were positive for the presence of free and 3 were positive for the presence of total anti-ustekinumab antibodies.
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