Severe Sepsis Cohorts Derived From Claims-Based Strategies Appear to be Biased Toward a More Severely Ill Patient Population*

Objective: The epidemiology of severe sepsis is derived from administrative databases that rely on International Classification of Diseases, 9th Revision, Clinical Modification (ICD–9-CM) codes to select cases. We compared the sensitivity of two code abstraction methods in identifying severe sepsis cases using a severe sepsis registry. Design: Single-center retrospective cohort study. Setting: Tertiary care, Academic, University Hospital. Patients: One thousand seven hundred thirty-five patients with severe sepsis or septic shock. Interventions: None. Measurements: Proportion identified as severe sepsis using two code abstraction methods: 1) the new specific ICD-9 codes for severe sepsis and septic shock, and 2) a validated method requiring two ICD-9 codes for infection and end-organ dysfunction. Multivariable logistic regression was performed to determine sociodemographics and clinical characteristics associated with documentation and coding accuracy. Main Results: The strategy combining a code for infection and end-organ dysfunction was more sensitive in identifying cases than the method requiring specific ICD-9 codes for severe sepsis or septic shock (47% vs. 21%). Elevated serum lactate level (p < 0.001), ICU admission (p < 0.001), presence of shock (p < 0.001), bacteremia as the source of sepsis (p = 0.02), and increased Acute Physiology and Chronic Health Evaluation II score (p < 0.001) were independently associated with being appropriately documented and coded. The 28-day mortality was significantly higher in those who were accurately documented/coded (41%, compared with 14% in those who were not, p < 0.001), reflective of a more severe presentation on admission. Conclusions: Patients admitted with severe sepsis and septic shock were incompletely documented and under-coded, using either ICD-9 code abstracting method. Documentation of subsequent coding of severe sepsis was more common in more severely ill patients. These findings are important when evaluating current national estimates and when interpreting epidemiologic studies of severe sepsis as cohorts derived from claims-based strategies appear to be biased toward a more severely ill patient population.