ICD-Coded Versus Undiagnosed Acute Kidney Injury in the Atherosclerosis Risk in Communities (ARIC) Study

Acute kidney injury (AKI) is common among older adults and associated with adverse outcomes, yet it often goes undiagnosed. We aimed to compare the prevalence of undiagnosed versus International Classification of Diseases (ICD)-coded AKI as well as their clinical and molecular characteristics and evaluate their associations with clinical outcomes.

Prospective cohort study.

A total of 5,692 adults with proteomic and metabolomic profiling from the Atherosclerosis Risk in Communities study, excluding individuals with end-stage kidney disease at baseline (2011-2013).

AKI, defined as either ICD-coded or undiagnosed based on 3 abstracted levels of serum creatinine measured during hospitalizations.

Incident coronary heart disease, heart failure, stroke, and all-cause mortality.

ICD-coded AKI was compared with undiagnosed AKI across all hospitalizations. Risk factors for ICD-coded and undiagnosed AKI were assessed separately using Cox proportional hazards models from study visit to the first AKI encounter. Time-varying Cox models were used to evaluate the associations of ICD-coded and undiagnosed AKI with adverse outcomes.

ICD codes identified 51.4% of AKI defined based on changes in serum creatinine, with higher sensitivity for more severe stages and a specificity of 87.0%. Undiagnosed AKI was more common in women; otherwise, clinical risk factors for undiagnosed AKI were similar to those for ICD-coded AKI, as were proteomic and metabolomic risk factors. Both AKI groups were strongly associated with coronary heart disease, heart failure, stroke, and mortality.

AKI was estimated using 3 values of serum creatinine only and not urinary output. Diagnosed AKI was identified using billing codes, which may underestimate clinical diagnosis of AKI.

Undiagnosed AKI is prevalent, especially among women, and is biologically and prognostically similar to ICD-coded AKI, motivating efforts to improve AKI recognition and diagnosis.