Nucleosome Monitoring Relevance for Outcome Prediction in Critically Ill Patients

Overview

NUROPI is a single-centre, prospective, non-interventional study in the Intensive Care Unit (ICU) of Erasme Hospital (Hôpital Universitaire de Bruxelles, Brussels, Belgium). Some critically ill patients get worse during the first days of their ICU stay. Identifying them early could allow faster escalation of care. Nucleosomes are fragments of DNA wrapped around proteins called histones. They are released into the blood when cells die or when white blood cells form neutrophil extracellular traps (NETs). High blood levels of nucleosomes may reflect inflammation, clotting activation and organ damage. This study will measure the H3.1 nucleosome in the blood of 1,000 consecutive adult ICU patients. The measurement uses a CE-marked laboratory test (Nu.Q® NETs, chemiluminescence immunoassay on the IDS-i10 analyser). No additional blood sample is taken for the study. H3.1 is measured on the leftover plasma of blood samples already drawn for routine care, at ICU admission, 6 hours, day 1, day 3 and day 7. Patient treatment is not changed. Patients, or their relatives or legal representative, receive an information notice and may refuse participation at any time. The main question is whether H3.1, alone or combined with routine ICU data, can identify patients at high risk of clinical deterioration within 72 hours of ICU admission. Other questions concern the link between H3.1 and mortality, organ dysfunction, and ICU treatments, and how H3.1 levels change during the first week.

Background Extracellular histones and nucleosomes act as damage-associated molecular patterns. They activate Toll-like receptors (TLR2, TLR4, TLR9), promote cytokine release, damage the endothelium and contribute to immunothrombosis. Circulating histone levels correlate with organ dysfunction severity in septic shock. Their prognostic value across the full spectrum of critical illness remains to be established. Objectives Primary objective: to evaluate the clinical performance of plasma H3.1, alone or combined with routine ICU parameters, for the early identification of ICU patients at high risk of clinical deterioration requiring timely escalation of care. Secondary objectives: to assess H3.1 as an independent prognostic marker of 28-day mortality after adjustment for established severity scores (Sequential Organ Failure Assessment version 2 \[SOFA-2\], Simplified Acute Physiology Score II \[SAPS II\]); to describe H3.1 kinetics over the first ICU week; to assess associations between H3.1 and organ dysfunction, vasopressor requirements, mechanical ventilation, renal replacement therapy (RRT) and venous thromboembolism (VTE); to compare H3.1 levels across diagnostic subgroups; to explore interactions between H3.1 and ICU therapies (anticoagulation, dexmedetomidine, corticosteroids, RRT, extracorporeal membrane oxygenation \[ECMO\]); to assess H3.1 as a potential enrichment biomarker for future trials targeting extracellular histones. Design Prospective, non-interventional, single-centre diagnostic-prognostic derivation and internal validation study. No procedure is performed for research purposes. H3.1 is measured on residual plasma (at least 100 µL) from routine K2-EDTA samples drawn through an arterial or central venous catheter already in place. Timepoints: ICU admission (H0), 6 hours (H6), day 1 (D1), day 3 (D3) and day 7 (D7). Plasma is analysed in batches by chemiluminescence immunoassay (Nu.Q® NETs, IDS-i10) and is not stored or biobanked beyond the study analyses. Participation is based on a non-opposition procedure. A deferred procedure may be used when neither the patient nor a representative can be informed at inclusion. Routine clinical data (including SOFA-2 and SAPS II) are recorded in REDCap. Population 1,000 consecutive adults admitted to the ICU within the previous 24 hours, all admission diagnoses combined. Enrolment is capped at 20 neurosurgical and 50 cardiac-surgery patients. Patients with active malignancy are included and analysed as a pre-specified subgroup. Primary endpoint Clinical deterioration, defined as an increase in SOFA-2 score of at least 2 points from admission within 72 hours, or ICU death within 72 hours. Secondary endpoints ICU, 28-day and 90-day all-cause mortality; vasopressor duration; mechanical ventilation duration; development of septic shock; ICU length of stay; VTE events; the primary composite endpoint at 48 hours; change in SOFA-2 from admission to day 7 (or ICU discharge if earlier); correlation between the change in SOFA-2 and the change in H3.1 from admission to 72 hours; H3.1 thresholds predicting poor outcomes across subgroups. Sample size and analysis The expected prevalence of the primary endpoint is 20% to 35%. With a null area under the receiver operating characteristic curve (AUROC) of 0.50, an anticipated AUROC of 0.75 and a two-sided alpha of 0.05, 1,000 patients provide more than 90% power across this range (Hanley and McNeil, 1982). At a central prevalence of 25%, about 250 events are expected, supporting up to 25 candidate predictors (at least 10 events per variable). An interim analysis is planned at 500 patients. Internal validation will use bootstrap resampling (1,000 iterations). A pre-specified sensitivity analysis will exclude patients with an admission SOFA-2 score of 15 or more. Reporting will follow STARD 2015 for H3.1 as a stand-alone test and TRIPOD 2024 for the combined prognostic model.