Improvement in the predictive ability of the Intermountain Mortality Risk Score by adding routinely collected laboratory tests such as albumin, bilirubin, and white cell differential count

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Abstract

Background:

The Intermountain Mortality Risk Score (IMRS), a sex-specific mortality-prediction metric, has proven to be effective in various populations. IMRS is comprised of the complete blood count (CBC), basic metabolic panel (BMP), and age. Whether the addition of factors from the comprehensive metabolic panel (CMP) and white blood cell (WBC) differential count improves risk stratification is unknown.

Methods:

Patients with baseline complete metabolic panel (CMP) and IMRS measurements were randomly assigned (60%/40%) to independent derivation (n=84,913) and validation (n=56,584) populations. A sex-specific risk score based on IMRS methods was computed in the derivation population using adjusted multivariable regression weights from all significant and noncollinear CMP [expanded IMRS (eIMRS)] and, when available, WBC differential components (eIMRS+diff).

Results:

Age averaged 67±16 years for females and 67±15 years for males. Receiver operator characteristic (ROC) c-statistics for 30-day death showed marked improvement for the eIMRS compared to the IMRS in both females [0.895 (0.882, 0.908) vs. 0.865 (0.850, 0.880)] and males [0.861 (0.847, 0.876) vs. 0.824 (0.807, 0.841)]. These results persisted for 1-year death: females [0.854 (0.847, 0.862) vs. 0.828 (0.819, 0.836)] and males [0.835 (0.826, 0.844) vs. 0.796 (0.789, 0.808)]. In addition, the eIMRS significantly improved risk reclassification. Further precision was seen when WBC differential components were included.

Conclusions:

The addition of the CMP components to the IMRS improved risk prediction. WBC differential also improved risk score predictive ability. These results suggest that the eIMRS may function even better than IMRS as a tool in patient care, risk-adjustment, and clinical research settings for predicting outcomes.

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