Reduced C-reactive protein level at hospital admission in patients treated with Tocilizumab – An attention may be required

Background: C-reactive protein (CRP) is a marker of inflammation and infection. The main proinflammatory cytokine that leads to CRP gene expression is IL-6. The study aimed to compare CRP level between patients who were treated with Tocilizumab (TCZ), an il-6 receptor blocker, and other advanced anti-inflammatory treatments (AAIT), as well as with other admitted and non-admitted populations. Methods: A cross-sectional study of all patients (≥18 years) hospitalized at tertiary medical center between December 2009 and February 2020 and treated before hospitalization with (AAIT). Only the first hospitalization of each patient was included. Women admitted to obstetrics department were excluded. Demographic data, first blood tests results, and comorbidities were collected. Results: The study included 563 patients treated with AAIT (2.5% received TCZ). Patients treated with TCZ were older (median 75 vs. 50 years, p < 0.001), had higher Charlson score (median 5 vs. 1, p < 0.001) and more infectious diseases at admission (50% vs. 23.4%, p = 0.05). Patients treated with TCZ had lower CRP levels (median 0.5 vs. 25 mg/l, p < 0.001) and more common normal values (64.3% vs. 20.8%, p < 0.001) compared to patients treated with other AAIT. CRP level in patients treated TCZ (median 0.5 mg/l) was lower than that of 58,548 patients admitted to the hospital between 2010 and 2020 (median 12.55 mg/l, p < 0.001) and not statistically different from 140 non-admitted randomly selected individuals without acute disease (1.33 mg/l, p = 0.294). Conclusion: Tocilizumab is associated with lower levels of CRP in patients admitted to acute care hospital. This finding must be considered by treating physician to avoid misinterpretation of CRP results.