Association between routine laboratory tests and long-term mortality among acutely admitted older medical patients: a cohort study

Abstract

Background: Older people have the highest incidence of acute medical admissions. Old age and acute hospital admissions are associated with a high risk of adverse health outcomes after discharge, such as reduced physical performance, readmissions and mortality. Hospitalisations in this population are often by acute admission and through the emergency department. This, along with the rapidly increasing proportion of older people, warrants the need for clinically feasible tools that can systematically assess vulnerability in older medical patients upon acute hospital admission. These are essential for prioritising treatment during hospitalisation and after discharge. Here we explore whether an abbreviated form of the FI-Lab frailty index, calculated as the number of admission laboratory test results outside of the reference interval (FI-OutRef) was associated with long term mortality among acutely admitted older medical patients. Secondly, we investigate other markers of aging (age, total number of chronic diagnoses, new chronic diagnoses, and new acute admissions) and their associations with long-term mortality.

Methods: A cohort study of acutely admitted medical patients aged 65 or older. Survival time within a 3 years post-discharge follow up period was used as the outcome. The associations between the markers and survival time were investigated by Cox regression analyses. For analyses, all markers were grouped by quartiles.

Results: A total of 4,005 patients were included. Among the 3,172 patients without a cancer diagnosis, mortality within 3 years was 39.9%. Univariate and multiple regression analyses for each marker showed that all were significantly associated with post-discharge survival. The changes between the estimates for the FI-OutRef quartiles in the univariate- and the multiple analyses were negligible. Among all the markers investigated, FI-OutRef had the highest hazard ratio of the fourth quartile versus the first quartile: 3.45 (95% CI: 2.83-s4.22, P < 0.001).

Conclusion: Among acutely admitted older medical patients, FI-OutRef was strongly associated with long-term mortality. This association was independent of age, sex, and number of chronic diagnoses, new chronic diagnoses, and new acute admissions. Hence FI-OutRef could be a biomarker of advancement of aging within the acute care setting.

Fig. 1

Cumulative incidence plots of mortality within 3 years post-discharge for patients without cancer diagnoses stratified by quartiles (Q1-Q4) of a: FI-OutRef, b: Age, c: No. of chronic diag., d: New chronic diag and e: New acute admissions. For proportion of cumulative mortality including 95% confidence interval (see Additional file 2: Appendix 2) Abbreviations: FI-OutRef: Frailty index by the number of admission laboratory tests outside the reference interval. No. of chronic diag: number of unique chronic diagnoses within the 10-year period prior to the index admission. New chronic diag: The number of chronic diagnoses given in the 2-year period preceding the index admission. New acute admissions: Number of new acute admissions within the 2-year period preceding the index admission. 1) Note: FI-OutRef includes 2,442 of the 2,965 discharged patients who had 10 or more standard laboratory tests analysed at admission

Fig. 2

a The number (#) of patients with admission laboratory test results outside (out) or inside (in) the reference interval (ref) and their corresponding proportion of mortality within 3 years from discharge. Significance of difference by Chi-Square * ~ P ≤ 0.001, ** ~ P ≤ 0.05. b differences in the mortality proportion for patients inside versus outside the reference interval. FI-OutRef: Frailty index by the number of admission laboratory test results outside the reference interval. MCHC: Mean corpuscular haemoglobin concentration. MCV: Mean corpuscular volume. BUN: Blood urea nitrogen. ALAT: Alanine aminotransferase. LDH: Lactate dehydrogenase. Coag. Fac. II,VII, X: Coagulation factor II, VII and X

Fig. 3

Cumulative incidence plots of mortality for in-hospital mortality for patients without cancer diagnoses stratified by quartiles (Q1-Q4) of a: FI-OutRef, b: Age, c: No. of chronic diag., d: New chronic diag and e: New acute admissions. For proportion of cumulative mortality including 95% confidence interval (see Additional file 2: Appendix 2). Abbreviations: FI-OutRef: Frailty index by the number of admission laboratory test results outside the reference interval. No. of chronic diag: the number of unique chronic diagnoses within the 10-year period prior to the index admission. New chronic diag: The number of chronic diagnoses given in the 2-year period preceding the index admission. New acute admissions: the number of new acute admissions within the 2-year period preceding the index admission. 1) Note: FI-OutRef includes 2,607 of the 3,172 included patients who had 10 or more standard laboratory tests at admission

Fig. 4

Cumulative incidence plots of mortality within 3 years post-discharge for patients with a cancer diagnoses stratified by quartiles (Q1-Q4) of a: FI-OutRef, b: Age, c: No. of chronic diag., d: New chronic diag and e: New acute admissions. For proportion of cumulative mortality including 95% confidence interval (see Additional file 2: Appendix 2). Abbreviations: FI-OutRef: Frailty index by the number of admission laboratory test results outside the reference interval. No. of chronic diag: the number of unique chronic diagnoses within the 10-year period prior to the index admission. New chronic diag: the number of chronic diagnoses given in the 2-year period preceding the index admission. New acute admissions: the number of new acute admissions within the 2-year period preceding the index admission. 1) Note: Analyses for FI-OutRef includes 714 of the 726 discharged patients who had 10 or more standard laboratory tests at admission