What is the SOFA Score?
The Sequential Organ Failure Assessment (SOFA) score is a clinical scoring system used to track the status and degree of organ dysfunction in critically ill patients, primarily those in intensive care units (ICUs). Originally developed in 1994 by Jean-Louis Vincent and colleagues for the European Society of Intensive Care Medicine, it was initially called the Sepsis-related Organ Failure Assessment but was later renamed to reflect its broader applicability to all critically ill patients, not just those with sepsis.
The SOFA score evaluates six organ systems — respiratory, coagulation, hepatic, cardiovascular, neurological, and renal — each scored from 0 (normal function) to 4 (severe dysfunction), yielding a total score ranging from 0 to 24. It is designed to be calculated daily, allowing clinicians to monitor the trajectory of organ failure over time.
SOFA Score Components
Each of the six organ systems is assessed using readily available clinical and laboratory parameters:
- Respiration: PaO2/FiO2 ratio (P/F ratio) — reflects the efficiency of gas exchange in the lungs
- Coagulation: Platelet count — decreased platelets indicate consumptive coagulopathy or bone marrow suppression
- Liver: Serum bilirubin — elevated levels indicate hepatic dysfunction or hemolysis
- Cardiovascular: Mean arterial pressure (MAP) and vasopressor requirements — reflects hemodynamic instability
- Central Nervous System: Glasgow Coma Scale (GCS) — assesses level of consciousness
- Renal: Serum creatinine and/or urine output — reflects kidney function
Scoring Table
| Organ System | Score 0 | Score 1 | Score 2 | Score 3 | Score 4 |
|---|---|---|---|---|---|
| Respiration PaO2/FiO2 | ≥400 | 300–399 | 200–299 | 100–199 + vent | <100 + vent |
| Coagulation Platelets (×10³/μL) | ≥150 | 100–149 | 50–99 | 20–49 | <20 |
| Liver Bilirubin (mg/dL) | <1.2 | 1.2–1.9 | 2.0–5.9 | 6.0–11.9 | ≥12.0 |
| Cardiovascular | MAP ≥70 | MAP <70 | Dopa ≤5 | Dopa >5 / Epi ≤0.1 | Dopa >15 / Epi >0.1 |
| CNS GCS | 15 | 13–14 | 10–12 | 6–9 | <6 |
| Renal Cr (mg/dL) or UO | <1.2 | 1.2–1.9 | 2.0–3.4 | 3.5–4.9 or UO<500 | ≥5.0 or UO<200 |
Note: Vasopressor doses are in mcg/kg/min. Dopamine and dobutamine doses refer to the infusion rate. UO = urine output in mL/day.
Mortality Correlation
The SOFA score correlates with ICU mortality. Higher scores indicate more severe organ dysfunction and higher mortality risk:
| SOFA Score | Estimated Mortality | Interpretation |
|---|---|---|
| 0–6 | <10% | Low mortality risk |
| 7–9 | 15–20% | Moderate mortality risk |
| 10–12 | 40–50% | High mortality risk |
| 13–14 | 50–60% | Very high mortality risk |
| 15–17 | >80% | Critical mortality risk |
| 18–24 | >90% | Near-fatal organ failure |
A change (delta) in SOFA score over time is also prognostically significant. An increase of ≥2 points from baseline is used in the Sepsis-3 definition to identify organ dysfunction attributable to infection.
Sepsis-3 and SOFA
In 2016, the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) fundamentally redefined sepsis as "life-threatening organ dysfunction caused by a dysregulated host response to infection." The SOFA score was chosen as the primary tool to operationalize this definition:
- Sepsis: Suspected or confirmed infection PLUS an acute increase in SOFA score ≥2 points from baseline (baseline assumed to be 0 if no pre-existing organ dysfunction)
- Septic Shock: Sepsis PLUS vasopressor requirement to maintain MAP ≥65 mmHg AND lactate >2 mmol/L despite adequate fluid resuscitation
This represented a major shift from the previous SIRS-based criteria, which were considered too sensitive and nonspecific. The Sepsis-3 definition emphasizes organ dysfunction as the defining feature of sepsis, rather than the inflammatory response itself.
qSOFA (Quick SOFA)
The Quick SOFA (qSOFA) was introduced as a bedside screening tool that can be rapidly assessed without laboratory values:
| qSOFA Criteria | Score |
|---|---|
| Respiratory rate ≥22 breaths/min | 1 |
| Altered mentation (GCS <15) | 1 |
| Systolic blood pressure ≤100 mmHg | 1 |
A qSOFA score ≥2 should prompt clinicians to look for organ dysfunction (via full SOFA score), consider the possibility of sepsis, and increase monitoring. However, qSOFA is a screening tool, not a diagnostic criterion for sepsis, and has been criticized for its modest sensitivity.
Serial SOFA Assessment
One of the key strengths of the SOFA score is its utility when assessed serially over time. Trends in the SOFA score provide important prognostic information:
- Increasing SOFA: Worsening organ dysfunction; associated with higher mortality
- Stable SOFA: No improvement; continued risk
- Decreasing SOFA: Improving organ function; better prognosis
- Delta SOFA (first 48h): An increase in SOFA ≥2 in the first 48 hours of ICU admission is strongly predictive of mortality
Limitations
- Sedation effects: GCS can be confounded by sedative medications in ventilated patients
- Chronic disease: Patients with baseline organ dysfunction (e.g., chronic kidney disease) may have elevated baseline scores
- Vasopressor practices: Cardiovascular scoring depends on local practices regarding vasopressor selection and dosing
- PaO2/FiO2 accuracy: Requires arterial blood gas; may not be available at all times
- Not validated for children: A pediatric version (pSOFA) exists with age-adjusted parameters
- Population differences: Mortality correlations were derived primarily from European and North American ICU populations
Worked Example
A 65-year-old patient admitted to the ICU with pneumonia and sepsis:
- PaO2/FiO2 = 180 on mechanical ventilation → Respiration = 3
- Platelets = 95 ×10³/μL → Coagulation = 2
- Bilirubin = 1.8 mg/dL → Liver = 1
- On norepinephrine at 0.08 mcg/kg/min → Cardiovascular = 3
- GCS = 13 → CNS = 1
- Creatinine = 2.5 mg/dL → Renal = 2
A SOFA score of 12 corresponds to an estimated mortality of 40–50%. Three organs have scores ≥3 (respiration, cardiovascular), indicating significant multi-organ dysfunction. This patient meets Sepsis-3 criteria (infection + SOFA ≥2 from baseline).
Frequently Asked Questions
How often should the SOFA score be calculated?
The SOFA score should ideally be calculated daily (every 24 hours) in ICU patients. In critically ill patients with rapidly changing status, it may be calculated more frequently. Serial assessment is crucial for tracking the trajectory of organ dysfunction.
What is the difference between SOFA and APACHE?
APACHE (Acute Physiology and Chronic Health Evaluation) is an admission scoring system that uses the worst values in the first 24 hours to predict hospital mortality. SOFA is designed for serial assessment and focuses specifically on organ dysfunction rather than overall physiologic derangement. SOFA is simpler, uses fewer variables, and is better suited for daily monitoring.
Can SOFA be used outside the ICU?
While SOFA was designed for ICU patients, the Sepsis-3 task force recommended using the SOFA score change to identify organ dysfunction in any patient with suspected infection. However, some components (PaO2/FiO2, vasopressors) are primarily relevant in ICU settings. The qSOFA was developed as an alternative screening tool for non-ICU settings.
How does SOFA relate to the old sepsis definitions?
The original sepsis definition (1991) was based on SIRS criteria (temperature, heart rate, respiratory rate, WBC count). Sepsis-2 (2001) added organ dysfunction criteria. Sepsis-3 (2016) eliminated SIRS and made organ dysfunction (SOFA ≥2) the central criterion. This change was driven by evidence that SIRS criteria were too nonspecific — up to half of hospitalized patients meet SIRS criteria without having sepsis.
What is a "significant" change in SOFA score?
An increase of ≥2 points from baseline is considered clinically significant and is used in the Sepsis-3 definition. A decrease of ≥2 points generally indicates meaningful clinical improvement. Even a 1-point change can be meaningful for individual organ systems.