..we created a frailty index from routine admission laboratory investigations (FI-Laboratory) linked to data comprising hospital outcomes.
..We found that the FI-Laboratory correlated weakly with the Clinical Frailty Scale (CFS; r2 = 0.09). An increase in the CFS and the equivalent of 3 additional abnormal laboratory test results in the FI-Laboratory, respectively, were associated with an increased proportion of inpatient days (rate ratios [RRs] 1.43, 95% confidence interval [CI] 1.35–1.52; and 1.47, 95% CI 1.41–1.54), discharge to a higher level of care (odd ratios [ORs] 1.39, 95% CI 1.27–1.52; and 1.30, 95% CI 1.16–1.47) and increased readmission rate (hazard ratios [HRs] 1.26, 95% CI 1.17–1.37; and 1.18, 95% CI 1.11–1.26). Increases in the CFS and FI-Laboratory were associated with increased mortality HRs of 1.39 (95% CI 1.28–1.51) and 1.45 (95% CI 1.37–1.54), respectively.
INTERPRETATION: We determined that FI-Laboratory, distinct from baseline frailty, could be used to predict risk of many adverse outcomes. The score is therefore a useful way to quantify the degree of acute illness in frail older adults.