Playing by the Rules: Using Decision Rules Wisely Part 2, Nontraumatic Conditions

A score of 0-1 of these criteria characterized low mortality risk (<1.5%) in the test group, a score of 2 was intermediate mortality risk (9.2%), and a score of 3 or more associated with high mortality risk (22%). A score ≥ 2 was 93% sensitive and 49% specific for 30-day mortality.⁶³

A subsequent prospective validation study by Aujesky et al that included 3181 patients with community-acquired pneumonia demonstrated slightly higher mortality rates for each CURB-65 score (0.6%, 3%, 6.1%, 13%, 17%, 43% mortality in scores of 0-5, respectively).⁶⁴ In particular, the 3% mortality rate in CURB-65 scores of 1 is similar to PSI class III mortality rates, suggesting a lower threshold (CURB-65 ≥1) for consideration of admission for management. Another validation study by Capelastegui et al showed similar mortality rates to the derivation study for specific CURB-65 scores, but noted 53% of patients with a score of 1 also were found to have characteristics that were independent for a poor prognosis, and should be considered in the decision for outpatient or inpatient treatment.⁶⁵ Furthermore, a recent study found that of patients in the ED with a CURB-65 score of 1, 8% still required critical care intervention.⁶⁶ Thus, use of CURB-65 in screening for low-risk patients with community-acquired pneumonia is recommended to be limited to scores of 0. However, as with PSI, validation studies have yet to show predictive utility of scores suggesting severe pneumonia (CURB-65 ≥3) in predicting mortality or ICU requirement.^60,61

As validation studies have suggested only patients with a CURB-65 score of 0 are screened low risk enough for outpatient treatment, greater weight may be placed on utility of CRB-65 as a tool. This rule, initially proposed in the same study as CURB-65, omits blood urea nitrogen as a factor to only rely on history and physical exam data with a score of 0 indicating low risk.⁶³ In initial derivation and validation studies, this rule demonstrated <1.6% mortality risk with a score of 0, with risk increasing to 4-8.6% in scores of 1.^63,65 Multiple studies have compared CRB-65 and CURB-65, with only marginal but not statistically significant improvement in prognostic utility of CURB-65.^65,67 A meta-analysis of 1648 patients even showed only 0.5% mortality risk in CRB-65 ≤1; potentially including CRB-65 0-1 as low risk, though, would require further study.⁶⁸ Although multiple validation studies have also successfully stratified low risk to similar mortality risk (<1.6%), accuracy wanes with higher CRB-65 scores.⁶⁹

Several studies have directly compared CURB-65 and PSI both in terms of identifying low-risk patients and stratifying disease severity.^{60,61,64,68,70-72} Multiple studies have shown similar mortality risk in low-risk populations and have demonstrated sensitivities for mortality greater than 96% for CURB-65/CRB-65 = 0 and PSI class I-III, albeit with specificities ranging from 18-65%.^64,68,70 In stratifying patients into different levels of severity (ward vs ICU patients), PSI has shown slightly better sensitivity/specificity for mortality and/or ICU intervention, though neither is strong enough to significantly stratify severe pneumonia to serve as tools for directing inpatient management.^60,61

Comment: PSI, CRB-65, and CURB-65 have been well validated as screening tools for low-risk patients who should be treated as outpatients (CURB-65 or CRB-65 = 0, PSI class I and II). A moderate-risk population (CURB-65 = 1 or 2, PSI class III) may benefit from treatment as inpatient or outpatient at clinician judgement. Use of these tools for determining disease severity and possible ICU requirement is not as reliable, and other clinical factors should be considered.

Conclusion

This article provides an overview of several common clinical decision instruments and the evidence behind them. Ultimately, many institutions have incorporated clinical decision rules directly into the electronic medical record, and this strategy will not only increase their use, but hopefully collect further data on whether the instruments truly perform better than unstructured clinical judgement.