A functional diagnostic complexity index for rehabilitation medicine: Measuring the influence of many diagnoses on functional independence and resource use

Abstract

Objective: To develop an index that weights diagnostic information (International Classification of Diseases, 9th revision, Clinical Modification, or ICD-9-CM codes) by the extent to which it is expected to affect functional status and inpatient rehabilitation length of stay (LOS).Design: Eleven nationally prominent physiatrists assigned ICD-9-CM codes to ordinal categories by expected effect on functional recovery. A resulting functional diagnostic complexity index score was calculated for each patient by combining the ranked values of each ICD-9-CM code in the discharge record. Analyses were stratified across the 20 rehabilitation impairment categories (RICs) of the Functional Independence Measure-Function Related Groups.Data: Patients (182,254) discharged from 465 inpatient rehabilitation units in larger hospitals and free-standing rehabilitation hospitals in 1995.Results: High degrees of diagnostic complexity were associated with low levels of functional independence at admission within each of 20 RICs (Spearman R = .06 to .25). Depending on RIC, patients in the highest (compared with the lowest) complexity category had up to a 35% increase in rehabilitation LOS after accounting for the primary medical reason for rehabilitation and severity of disabilities at admission.Conclusion: This prototype index of medical complexity offers a promising approach for analyzing the cumulative effects of diagnoses on patients' initial functional status and rehabilitation LOS.