The MARINA study (bioMARkers of INflammation, infection, and immunity in critical cAre) is a multicenter, prospective and retrospective observational cohort study designed to evaluate the diagnostic and prognostic role of inflammatory and immune biomarkers in critically ill patients.

The study enrolls adult patients (≥18 years) admitted to intensive care or step-down units who present with signs or symptoms of active infection, including sepsis and septic shock. Three main patient populations are targeted: (1) patients with suspected or confirmed infection (community- or hospital-acquired); (2) patients undergoing high-risk major surgery (cardiac, thoracic, or abdominal) under general anesthesia; and (3) immunocompromised patients (solid organ transplant, HSCT, bone marrow transplant, CAR-T cell therapy, or other severe immunosuppression).

Serial measurements of established and emerging biomarkers - including procalcitonin, C-reactive protein, MR-proadrenomedullina, copeptin, ferritin, interleukin-6, troponin, D-dimer, lactate, lymphocyte subpopulations, and immunoglobulins - are collected at predefined time points (T1: within 24 hours; T2: within 72 hours; T7: at day 7 of ICU admission) and integrated with clinical data on a dedicated electronic platform.

The primary endpoint is 28-day mortality. Secondary endpoints include assessment of organ damage, clinical severity, response to treatment, infectious complications (including VAP and bacteremia), superinfections (bacterial, viral, fungal), ICU and hospital length of stay, and the ability of biomarkers to guide antimicrobial de-escalation. Long-term survival at 90 and 180 days is also assessed.

A minimum sample size of 200 patients (prospective phase) is planned across participating centers in Italy and Spain. The study duration is four years from ethical approval.

Inclusion Criteria:

• Age ≥ 18 years
• Written informed consent to participate in the study (or deferred consent, obtained as soon as clinically feasible, in patients unable to provide consent at the time of enrollment)
• Surgical group: patients who have undergone a high-risk elective or emergency surgical procedure under general anesthesia within the previous 24 hours (cardiac surgery, thoracic surgery, abdominal surgery)
• Infection group: suspected or confirmed infection (including sepsis and septic shock), either community- or hospital-acquired
• Immunocompromised group (subset of the infection group): patients with impaired immune status, including solid organ transplant (SOT) recipients, hematopoietic stem cell transplant (HSCT) recipients, bone marrow transplant recipients, CAR-T cell therapy recipients, or any other form of severe immunosuppression

Exclusion Criteria:

• Refusal to provide informed consent
• Age < 18 years
• Pregnancy
• Therapeutic limitations or clinical decision to withdraw or withhold life-sustaining treatment at the time of enrollment

The study enrolls adult patients (aged ≥18 years) admitted to intensive care units (ICU) or step-down units at participating centers. Three partially overlapping patient populations are included:

• Infection group: patients with suspected or confirmed infection, including sepsis and septic shock, either community- or hospital-acquired.
• Surgical group: patients who have undergone high-risk major surgery under general anesthesia (cardiac, thoracic, or abdominal surgery) within the 24 hours preceding ICU admission, either as elective or emergency procedures.
• Immunocompromised group: patients with severely impaired immune status, including recipients of solid organ transplant (SOT), hematopoietic stem cell transplant (HSCT), bone marrow transplant, or CAR-T cell therapy, as well as patients under any other form of severe immunosuppression, presenting with signs or symptoms of active infection.