International Classification Of Disease Coding Of Exertional Heat Illnesses In US Army Soldiers

Abstract

The severity of exertional heat illnesses (EHI) ranges from relatively minor heat exhaustion to potentially life-threatening heat stroke. Epidemiological surveillance of the types of and trends in EHI incidence depends on application of the appropriate International Classification of Disease, 9th Revision (ICD-9) diagnostic code. However, data examining whether the appropriate EHI ICD-9 code is selected are lacking. PURPOSE: To determine whether the appropriate ICD-9 code is selected in a cohort of EHI casualties. METHODS: Chart reviews of 290 EHI casualties that occurred in US Army soldiers from 2009-2012 were conducted. The ICD-9 diagnostic code was extracted, as were the initial and peak values for AST, ALT, creatine kinase (CK) and creatinine (Cr). Diagnostic criteria for heat injury and heat stroke include evidence of organ and/or tissue damage; 2 out of 3 of the following must have been met to be considered heat injury (ICD-9 code 992.8) or heat stroke (ICD-9 code 992.0): AST/ALT fold increase >3, CK fold increase >5, and/or Cr ≥1.5mg/dL. By-year and all-years contingency tables were constructed from which sensitively, specificity, and positive and negative predictive value were calculated. RESULTS: The 290 cases examined represent ~29% of all EHI at Ft Benning and ~6% of all EHI Army-wide during the study period. There were 80 cases that met the laboratory diagnostic criteria for heat injury/stroke, however of those, 28 cases were diagnosed as an EHI other than heat injury/stroke (sensitivity=0.65). 210 cases did not meet the laboratory diagnostic criteria but 66 of those were incorrectly diagnosed as heat injury or heat stroke (specificity=0.69). Positive and negative predictive values were 0.44 and 0.84, respectively. In total, the incorrect ICD-9 code was applied to 94 of 290 total cases. Comparison of by-year contingency tables indicated considerable variability but no discernable trends were evident. CONCLUSIONS: Our data suggest that caution is warranted when examining epidemiological surveillance data on EHI severity, as there was disagreement between the laboratory data and the selected ICD-9 code in ~1/3 of all cases in this cohort.