Complementing chronic frailty assessment at hospital admission with an electronic frailty index (FI-Laboratory) comprising routine blood test results

Abstract

Background: Acutely ill and frail older adults have complex social and health care needs. It is important to understand how this complexity affects acute outcomes for admission to hospital. We validated a frailty index using routine admission laboratory tests with outcomes after patients were admitted to hospital.

Methods: In a prospective cohort of older adults admitted to a large tertiary hospital in the United Kingdom, we created a frailty index from routine admission laboratory investigations (FI-Laboratory) linked to data comprising hospital outcomes. We evaluated the association between the FI-Laboratory and total days spent in hospital, discharge to a higher level of care, readmission and mortality.

Results: Of 2552 admissions among 1750 older adults, we were able to generate FI-Laboratory values for 2254 admissions (88.3% of the cohort). More than half of admitted patients were women (55.3%) and the mean age was 84.6 (SD 14.0) years. We found that the FI-Laboratory correlated weakly with the Clinical Frailty Scale (CFS; r ² = 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.

Figure 1:

Proportion of participants who were readmitted to hospital calculated by using a multivariable Cox regression model for readmission adjusted up and down by hazard ratios from the A) CFS and B) FI-Laboratory. Curves use the multivariable Cox model with a participant age of 75 years, no dementia (0), male (0), no delirium (0), admitted from home (0), no history of falls (0), and either 8 abnormal laboratory values (Panel A) or a CFS of “6-Moderately Frail” (Panel B). Note: CFS = Clinal Frailty Scale, FI-Laboratory = Frailty Index of common laboratory tests.

Figure 2:

Kaplan–Meier curves adjusted by A) the hazard ratios of CFS scores and B) quartiles of the FI-Laboratory as estimated in the multivariable Cox model. Survival curves use the multivariable Cox model with a participant age of 75 years, no dementia (0), male (0), no delirium (0), admitted from home (0), no history of falls (0), and either 8 abnormal laboratory values (Panel A) or a CFS of “6-Moderately Frail” (Panel B). Note: CFS = Clinal Frailty Scale, FI-Laboratory = Frailty Index of common laboratory tests.