SOFA score
The Sequential Organ Failure Assessment (SOFA) score is a clinical scoring system used to quantify the severity of organ dysfunction in critically ill patients, particularly in intensive care settings for conditions like sepsis. It evaluates dysfunction across six organ systems—respiratory, cardiovascular, hepatic, coagulation, renal, and central nervous system—by assigning a score from 0 (normal function) to 4 (most severe dysfunction) for each, resulting in a total score ranging from 0 to 24; higher scores are associated with increased mortality risk.[1] Scores above 15 indicate a mortality rate exceeding 90% in sepsis cases.[2] Developed in 1994 during a consensus conference organized by the Working Group on Sepsis-Related Problems of the European Society of Intensive Care Medicine, the SOFA score was first published in 1996 as a simple, repeatable tool to describe rather than predict organ failure, allowing for daily bedside assessments using readily available clinical and laboratory data.[3] Originally termed the Sepsis-related Organ Failure Assessment score, it was renamed "Sequential" in 1998 to broaden its application beyond sepsis to any critically ill patient, emphasizing its utility in tracking changes over time rather than static prognosis.[4] The score's components are based on specific, objective variables: respiration uses the ratio of arterial oxygen partial pressure (PaO₂) to fractional inspired oxygen (FiO₂); coagulation assesses platelet count; liver function is measured by serum bilirubin; cardiovascular status considers mean arterial pressure or vasopressor requirements; neurological function employs the Glasgow Coma Scale; and renal function evaluates serum creatinine or urine output.[4] Clinically, the SOFA score facilitates patient monitoring in ICUs, supports research on organ failure, aids in sepsis management per international guidelines like the Surviving Sepsis Campaign, and has been adapted for resource allocation during crises, such as pandemics, though it is not intended for individual outcome prediction or as a standalone triage tool.[1] In 2024, an updated version called SOFA-2 was published to incorporate modern critical care practices and address some limitations of the original score.[5] Despite its widespread validation across diverse populations and settings, limitations include reliance on invasive measurements like arterial blood gases and potential inaccuracies in low-resource environments or with modern therapies like extracorporeal support.[4]Introduction
Definition and Purpose
The Sequential Organ Failure Assessment (SOFA) score is a standardized scoring system designed to quantify the degree of organ dysfunction and failure in critically ill patients by evaluating performance across six organ systems. Each system is graded on a scale from 0 (normal function) to 4 (most abnormal), yielding a composite score ranging from 0 to 24, with higher values reflecting increasing severity of multiorgan dysfunction.[6] Developed initially as the Sepsis-related Organ Failure Assessment, it was renamed "Sequential" to emphasize its applicability to all ICU patients beyond just those with sepsis, allowing for repeatable measurements to capture dynamic changes in organ status.[7] This description refers to the original SOFA score; an updated version, SOFA-2, was published in 2025 to incorporate contemporary organ support therapies and revised thresholds.[5] The primary purpose of the SOFA score is to offer an objective, serial assessment of organ function in the intensive care unit (ICU), facilitating the monitoring of disease progression, response to therapy, and overall clinical trajectory in patients at risk of multiorgan failure. In conditions like sepsis, where organ dysfunction often evolves rapidly along a continuum from mild impairment to life-threatening failure, the SOFA enables clinicians to standardize evaluations and guide decisions on interventions such as fluid resuscitation or vasopressor support.[1] While the score correlates with mortality— for instance, scores exceeding 15 are associated with high in-hospital death rates—its core intent is descriptive rather than predictive, distinguishing it from broader severity indices like APACHE.[7]Historical Development
The development of the SOFA (Sequential Organ Failure Assessment) score originated from a need to standardize the evaluation of organ dysfunction in critically ill patients, particularly those with sepsis. In October 1994, the European Society of Intensive Care Medicine (ESICM) convened a consensus meeting in Paris, organized by its Working Group on Sepsis-Related Problems of the ESICM, to address inconsistencies in assessing sepsis-related organ failure across intensive care units (ICUs). This effort aimed to create a simple, objective tool for describing and quantifying organ dysfunction/failure, facilitating better clinical decision-making, research comparability, and resource allocation in ICUs.[8][9] The SOFA score was formally introduced in a seminal publication in 1996 by Vincent et al., on behalf of the ESICM Working Group, in Intensive Care Medicine. This paper outlined the score's framework, emphasizing its design to track changes in organ function over time rather than provide a static prognostic estimate. The development drew on expert consensus to select six key organ systems and define graded levels of dysfunction, ensuring the tool was practical for daily ICU use without requiring specialized equipment.[8][3] Initial validation occurred through a multicenter prospective study published in 1998 by Vincent et al. in JAMA, involving 1,449 critically ill patients across 40 ICUs in 16 countries. The study demonstrated the SOFA score's reliability in quantifying the incidence and evolution of organ dysfunction, particularly in sepsis cases, with repeated assessments revealing dynamic patterns that correlated with clinical progression. This validation underscored the score's utility for monitoring patient trajectories beyond admission severity.[2] By the early 2000s, the SOFA score gained widespread adoption, notably integrated into the Surviving Sepsis Campaign's first international guidelines in 2004 for assessing sepsis severity and guiding management protocols. This incorporation solidified its role in mortality prediction and standardized care, influencing global ICU practices and subsequent sepsis definitions.[10]Original SOFA Score
Components and Organ Systems
The original SOFA score evaluates dysfunction across six key organ systems, selected for their frequent involvement in critical illness and the objectivity of the associated clinical measures. These systems include the respiratory, cardiovascular, hepatic, coagulation, renal, and neurological systems, with each assessed using specific, readily available laboratory or clinical variables to allow for consistent monitoring.[3] Each system is graded on a scale from 0 (normal) to 4 (most abnormal), providing a framework for tracking sequential changes in organ function.[4] Respiratory system: This component measures pulmonary oxygenation through the ratio of partial pressure of arterial oxygen (PaO₂) to the fraction of inspired oxygen (FiO₂), which reflects the efficiency of gas exchange in the lungs and is influenced by factors such as ventilation strategies and underlying lung pathology. Cardiovascular system: Assessment focuses on hemodynamic stability via mean arterial pressure (MAP) or the requirement for vasopressors, such as dopamine or norepinephrine equivalents, to maintain adequate perfusion in the context of shock or distributive failure.[3] Hepatic system: Liver function is gauged by serum bilirubin levels, an indicator of synthetic capacity and potential cholestasis or hepatocellular injury commonly seen in sepsis-induced multiorgan dysfunction. Coagulation system: Platelet count serves as the primary variable, capturing thrombocytopenia arising from consumption, bone marrow suppression, or disseminated intravascular coagulation in critically ill patients.[3] Renal system: Kidney performance is evaluated using serum creatinine concentration or urine output, both of which highlight glomerular filtration rate and tubular function impairments due to hypoperfusion or direct toxic effects. Neurological system: The Glasgow Coma Scale (GCS) quantifies level of consciousness and neurological integrity, accounting for alterations from metabolic derangements, ischemia, or inflammation in severe illness.[3] The selection of these systems and variables emphasizes their prevalence in sepsis-related organ failure, ease of measurement in intensive care settings, and ability to provide objective, repeatable assessments without relying on subjective interpretations.[4]Calculation and Scoring
The Sequential Organ Failure Assessment (SOFA) score evaluates organ dysfunction across six systems—respiratory, cardiovascular, hepatic, coagulation, renal, and neurological—by assigning a score from 0 (indicating normal function) to 4 (indicating most abnormal function) for each system based on specific physiological parameters. The total SOFA score is the sum of these individual scores, ranging from 0 to 24, with higher values reflecting greater overall organ dysfunction. This summation is expressed as: Total SOFA = Respiratory score + Cardiovascular score + Hepatic score + Coagulation score + Renal score + Neurological score.[6] To compute the score, the worst values within a 24-hour period are used for each parameter, allowing for serial assessments over time. Changes in SOFA scores, known as delta-SOFA (e.g., the difference between baseline and subsequent scores), provide insight into the progression or resolution of organ failure. The scoring criteria for each organ system are detailed below, derived from standardized thresholds established in the original SOFA framework.| Organ System | Parameter | Score 0 | Score 1 | Score 2 | Score 3 | Score 4 |
|---|---|---|---|---|---|---|
| Respiratory | PaO₂/FiO₂ (mmHg) | ≥400 | <400 | <300 | <200 (with respiratory support) | <100 (with respiratory support) |
| Cardiovascular | Mean arterial pressure (MAP, mmHg) or vasopressor use (μg/kg/min) | MAP ≥70 | MAP <70 | Dopamine ≤5 (or any dobutamine) | Dopamine >5, ≤15; or epinephrine/norepinephrine ≤0.1 | Dopamine >15; or epinephrine/norepinephrine >0.1 |
| Hepatic | Bilirubin (mg/dL) | <1.2 | 1.2–1.9 | 2.0–5.9 | 6.0–11.9 | >12.0 |
| Coagulation | Platelets (×10³/μL) | ≥150 | <150 | <100 | <50 | <20 |
| Renal | Creatinine (mg/dL) or urine output (mL/day) | <1.2 | 1.2–1.9 | 2.0–3.4 | 3.5–4.9 (or urine output <500) | >5.0 (or urine output <200) |
| Neurological | Glasgow Coma Scale | 15 | 13–14 | 10–12 | 6–9 | <6 |
Clinical Applications
Use in Sepsis and ICU Settings
The SOFA score is integral to sepsis management protocols as outlined in the Surviving Sepsis Campaign (SSC) guidelines, first published in 2004, where it serves to quantify organ dysfunction in patients with suspected infection. Specifically, an acute increase in the total SOFA score of 2 or more points from baseline—assumed to be zero in patients without known preexisting organ dysfunction—identifies sepsis and triggers the activation of evidence-based sepsis bundles, including early administration of broad-spectrum antibiotics, intravenous fluid resuscitation, and measures for source control.[11] In intensive care unit (ICU) settings, the SOFA score facilitates ongoing monitoring of critically ill patients with sepsis through serial assessments, typically performed every 24 to 48 hours, to evaluate the trajectory of organ failure and responsiveness to interventions such as fluid boluses, vasopressor support, and antimicrobial therapy. This dynamic tracking allows clinicians to detect worsening multiorgan dysfunction early, guiding adjustments in treatment strategies to mitigate progression. For instance, a sustained or rising SOFA score may indicate inadequate response, prompting reevaluation of the underlying infection or hemodynamic status.[12][13] Clinical protocols often incorporate SOFA thresholds to escalate care in sepsis cases; an increase exceeding 2 points, for example, signals the need for intensified interventions, such as advanced organ support or consultation with specialists, to prevent further deterioration. In landmark trials like the ProCESS (Protocolized Care for Early Septic Shock) study and the ARISE (Australasian Resuscitation in Sepsis Evaluation) trial, the SOFA score played a key role in risk stratification by establishing baseline organ dysfunction severity among enrolled patients with septic shock, enabling subgroup analyses and evaluation of treatment effects on organ recovery.[14]Prognostic Utility
The Sequential Organ Failure Assessment (SOFA) score exhibits robust prognostic utility in predicting short-term mortality among critically ill patients in intensive care units (ICUs). A SOFA score of 15 or greater is associated with an ICU mortality rate exceeding 90%, as demonstrated in early validation efforts across diverse patient populations. In sepsis cohorts, the SOFA score's discriminatory ability for in-hospital mortality yields an area under the receiver operating characteristic (ROC) curve typically ranging from 0.75 to 0.85, reflecting moderate to good performance in stratifying risk. A 2023 meta-analysis of 32 studies involving over 55,000 patients further supports this, reporting pooled sensitivity and specificity of approximately 0.73 and 0.70, respectively, for mortality prediction in sepsis.[15] Longitudinal assessments enhance the SOFA score's predictive power beyond static baseline measurements. The change in SOFA score (ΔSOFA) over the first 48 hours of ICU admission outperforms the initial score in forecasting 28-day mortality; specifically, any increase during this interval correlates with a mortality rate of at least 50%, irrespective of the starting value, while a decrease signals a much lower risk of approximately 6% for initial scores ≤11. This dynamic evaluation captures evolving organ dysfunction more effectively than a single-point assessment. The SOFA score's prognostic validity was established in a seminal 1998 multicenter prospective study of 1,449 patients across 40 ICUs in 16 countries, which showed that higher scores reliably tracked organ dysfunction progression and correlated with increased mortality, with nonsurvivors exhibiting greater score increases over time. Meta-regression analyses of randomized controlled trials, including those beyond sepsis (such as in cardiac arrest and pancreatitis), confirm the score's broad applicability in non-sepsis ICU settings, where ΔSOFA explains up to 32% of variability in mortality outcomes. Despite these strengths, the SOFA score's prognostic accuracy diminishes for long-term outcomes extending beyond 28 days, as fixed or delta scores show weaker associations with extended survival due to factors like post-ICU recovery dynamics not captured by the tool.Quick SOFA Score (qSOFA)
Criteria and Calculation
The quick Sequential Organ Failure Assessment (qSOFA) score is a simplified bedside tool designed to identify patients at high risk of poor outcomes due to sepsis outside of intensive care settings, using only three clinical criteria derived from vital signs and mental status assessment.[11] These criteria were selected based on their ability to predict mortality in emergency department and ward patients with suspected infection, without requiring laboratory tests or complex computations.[16] The three qSOFA criteria are:- Respiratory rate of 22 breaths per minute or greater
- Altered mentation, defined as a Glasgow Coma Scale score less than 15
- Systolic blood pressure of 100 mm Hg or less