A New Severity Scoring Scale for the Three Minute Confusion Assessment Method (3D-CAM)

To the Editor

The 3D-CAM is a short, structured instrument to determine the presence or absence of CAM-defined delirium that can be completed in about 3 minutes.¹ Recent literature has emphasized the importance of measuring delirium severity in addition to determining its presence.² Some of us previously reported a method for measuring delirium severity using the 3D-CAM with scores ranging from 0–7, where 7 is the most severe.³ This method has numerous strengths, including: it quantifies the severity of each of the four features measured by the 3D-CAM, and assigns non-zero severity scores only to those patients who are highly likely to have delirium by gold-standard clinical assessments. For some applications, it is also important to have a delirium severity scoring scale that captures the severity of sub-syndromal delirium symptoms, and has a wider range for quantifying the severity of delirium signs and symptoms. This latter feature is particularly important in delirium biomarker studies,^4–9 in which delirium severity scores with a wider range would provide greater statistical power for detecting associations with biomarkers. A delirium severity score with a wider range may also be useful for tracking the severity of delirium over time within individual patients, in both clinical practice and research studies.

Thus, we developed and validated a new delirium severity scoring method based on the 3D-CAM instrument that yields an expanded “raw” severity score ranging from 0–20 points. This “raw” score is the sum of “positive” items present on 20 questions of the original 3D-CAM instrument, where positivity is defined as an incorrect response to a cognitive test item (3D-CAM items 1–7), patient endorsement of a symptom probe (items 8–10) or interviewer endorsement of an observational feature (items 11–20).¹ To describe and validate the new “raw” 3D-CAM severity measure, we calculated 3D-CAM severity scores using both the old and new method in the original 3D-CAM validation cohort stratified by the presence or absence of delirium determined by an independent clinical reference standard assessment, and also by the 3D-CAM itself.¹ We then calculated the discriminant measure area under the ROC (AUC), and the 95% Wald confidence interval (CI) assuming asymptotic normality of the estimated area, for both severity measures against the presence or absence of delirium measured both ways. The first provides a measure of external validity against an independent reference standard, while the second provides a measure of internal consistency between 3D-CAM delirium severity and diagnosis. Informed consent was obtained for all study procedures, and analyses were performed using SAS Version 9.4.

The distribution of severity scores in patients with versus without delirium from a previously described cohort of 201 older adults (mean age 84 years, 62% women, 28% with dementia)¹ is shown in Supplemental Tables 1A and 1B, for both the “original” 3D-CAM severity scoring scale and for this new “raw” 3D-CAM severity scoring scale, respectively. As expected, the new “raw” severity scale has a wider range than the original severity scale (17 vs. 6 points), including among those with delirium (16 vs. 6 points) and those without delirium (8 vs. 5 points; Supplemental Tables 1A, 1B). The AUC(95% CI) was 0.950(0.951–0.984) for the “original” 3D-CAM severity score and 0.950(0.914–0.986) for the new “raw” 3D-CAM severity score for discriminating the presence or absence of delirium as determined by an independent reference standard clinical interview (Fig 1A). For discriminating the presence or absence of delirium determined by the 3D-CAM, the AUC(95% CI) was 0.979(0.965–0.993) for the “original” 3D-CAM severity score and 0.986(0.965–0.993) for the “raw” 3D-CAM severity score (Fig 1B).

Figure 1:

Receiver operating characteristic (ROC) curves for prediction of delirium presence or absence, as determined by an independent clinical reference standard assessment in (A) and by the 3D-CAM in (B), using the indicated delirium severity scoring method.

These data suggest that this new “raw” 3D-CAM delirium severity scoring method has a wide range, demonstrates high validity against an independent clinical reference standard, and strong internal consistency with the 3D-CAM delirium diagnosis. In the last instance, it works similarly well as the previously described “original” 3D-CAM severity scoring method.³ This new “raw” 3D-CAM delirium severity scoring method provides two clear advantages. First, it has a nearly 3-fold wider range for assessing delirium severity than the original 3D-CAM severity scoring method,³ which may be useful for both delirium biomarker studies and for tracking the clinical course of individual patients’ delirium over time. Second, the new method’s wider range among the non-delirious allows one to quantitate the severity of sub-syndromal delirium, i.e. the severity of delirium-related signs and symptoms that may be present, yet insufficient to meet full diagnostic criteria for delirium. Future work should evaluate the relationship between this new “raw” 3D-CAM delirium severity score and clinical outcomes such as hospital length of stay, readmission rate and mortality.