Clinical background
qSOFA was introduced in the Sepsis-3 consensus document in 2016 in response to the lack of discriminatory power of the SIRS criteria: they are met in a large proportion of inpatients without infection and are not associated with mortality [1]. At the same time, clinicians outside intensive care needed a rapid tool to identify patients with suspected infection at high risk of developing sepsis with organ failure, without waiting for laboratory results.
qSOFA is constructed as a prognostic marker, not as a diagnostic criterion. Sepsis-3 defines sepsis as infection plus an increase in the full SOFA score of at least 2 points, which requires laboratory data [1]. qSOFA is instead intended to prompt further investigation and escalation of management in patients outside the ICU.
Calculating qSOFA
The score consists of three variables, each worth 0 or 1 point:
The range is 0 to 3 points. A score of 2 or more is regarded as positive and identifies patients at higher risk of a poor outcome [1].
The derivation was performed by Seymour et al. in a retrospective cohort of 1.3 million encounters at 12 hospitals in southwestern Pennsylvania from 2010 to 2012 [2]. Of these, 148,907 encounters involved suspected infection, defined as the combination of antibiotics and cultures within a specified time window. The cohort was randomly divided into a derivation group (n = 74,453) and a validation group (n = 74,454). The primary outcome was in-hospital mortality, which was 4 per cent overall. qSOFA was derived by multivariable logistic regression with forward selection and simplification to one point per variable regardless of the size of the regression coefficients. Confirmatory analyses were performed in four external datasets comprising 706,399 encounters from 165 hospitals in the USA and Germany, including prehospital, emergency department and ward encounters [2].
Interpretation in practice
| qSOFA | Interpretation | Clinical action |
|---|---|---|
| 0–1 | Low to moderate risk | Not sufficient to exclude sepsis. Continue clinical assessment, consider other reasons for escalation. |
| ≥2 | Increased risk of a poor outcome | Escalate: increased monitoring, blood cultures, lactate, assess the need for antibiotics and fluids, consider intensive care review. |
In the derivation cohort, a qSOFA ≥2 was associated with a 3- to 14-fold increase in in-hospital mortality across all deciles of baseline risk [2]. It is this gradient that has given the score its clinical value: it identifies a group of patients whose risk is measurably raised regardless of their underlying burden of illness.
The score should not be used as a binary test. A patient with a qSOFA of 0 or 1 may well have sepsis, and in a patient who looks unwell a low value must not lead to management being scaled back.
Validation and performance
In the derivation study, qSOFA performed best outside the ICU. In the non-ICU encounters of the validation cohort (n = 66,522, of whom 1,886 died), the AUC for in-hospital mortality was 0.81 (95% CI 0.80–0.82), statistically significantly better than both SOFA (AUC 0.79) and SIRS (AUC 0.76) [2]. In the ICU the position was reversed: qSOFA had an AUC of 0.66 (95% CI 0.64–0.68) and was inferior to SOFA (AUC 0.74) and LODS (AUC 0.75) [2].
A systematic review and meta-analysis from 2018, based on 23 studies with 146,551 patients outside the ICU, showed that a qSOFA ≥2 had a pooled sensitivity of 0.51 (95% CI 0.39–0.62) and a specificity of 0.83 (95% CI 0.74–0.89) for in-hospital mortality [3]. The AUC was 0.74 (95% CI 0.70–0.78), not significantly different from SIRS (AUC 0.71). For predicting acute organ failure the sensitivity was even lower, 0.47, despite a high AUC (0.87) [3]. The low sensitivity is the most consistent finding in the validation literature and is the score's principal weakness.
In low- and middle-income countries, qSOFA alone has limited predictive ability. In a prospective cohort from Southeast Asia of 4,980 inpatients with suspected infection, the AUC for 28-day mortality was 0.68 (95% CI 0.67–0.70) for qSOFA alone [4]. Adding a points-based lactate level improved discrimination to an AUC of 0.78 (95% CI 0.76–0.80), on a par with a modified SOFA score [4]. Patients with a qSOFA of 3 had a 28-day mortality of 51 per cent in this cohort.
Limitations
qSOFA is not a screening instrument with high sensitivity. Half of the patients who die or develop organ failure will have a qSOFA <2 [3]. Using the score to exclude sepsis in a patient who appears unwell is therefore wrong.
The score is not validated for ICU patients, in whom the full SOFA score should be used instead [1, 2]. Nor was it developed for children or for patients without suspected infection. qSOFA says nothing about the aetiology or focus of the infection.
A common mistake is to equate a qSOFA ≥2 with a diagnosis of sepsis. Sepsis-3 defines sepsis by an increase in the SOFA score of at least 2, which requires laboratory values and a baseline measurement [1]. qSOFA is a prompt to begin that investigation, not a substitute for it.
The three variables can be affected by factors unrelated to sepsis: the respiratory rate by pain or anxiety, the blood pressure by posture or medication, the level of consciousness by sedation or intoxication. This lowers specificity in clinical practice compared with the databases in which the score was derived.
References
- Singer M, Deutschman CS, Seymour CW et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA 2016. PMID: 26903338
- Seymour CW, Liu VX, Iwashyna TJ et al. Assessment of Clinical Criteria for Sepsis: For the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA 2016. PMID: 26903335
- Song JU, Sin CK, Park HK et al. Performance of the quick Sequential (sepsis-related) Organ Failure Assessment score as a prognostic tool in infected patients outside the intensive care unit: a systematic review and meta-analysis. Critical Care 2018. PMID: 29409518
- Wright SW, Hantrakun V, Rudd KE et al. Enhanced bedside mortality prediction combining point-of-care lactate and the quick Sequential Organ Failure Assessment (qSOFA) score in patients hospitalised with suspected infection in southeast Asia: a cohort study. Lancet Global Health 2022. PMID: 35961351
