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False-positive coding for acute myocardial infarction on hospital discharge records: chart audit results from a
C van Walraven1, B Wang, A M Ugnat
1Faculty of Medicine, University of Toronto, Ontario.
Insights
A review of 209 charts found 21% were false-positives for acute myocardial infarction coding. This highlights issues with International Classification of Diseases (ICD-9-CM) coding accuracy for myocardial infarction.
Area of Science:
- Medical Informatics
- Cardiology
- Health Services Research
Background:
- Hospital medical records staff use the International Classification of Diseases (Clinically Modified), Ninth Revision (ICD-9-CM) for diagnostic coding.
- Accurate coding is crucial for healthcare statistics, research, and resource allocation.
Purpose of the Study:
- To assess the accuracy of acute myocardial infarction coding in a tertiary hospital.
- To identify reasons for coding discrepancies and inform potential improvements in the ICD-9-CM system.
Main Methods:
- Review of 209 consecutive hospital charts coded for acute myocardial infarction as the primary diagnosis.
- Application of defined criteria (symptomatic, electrocardiographic, enzymatic) to verify the diagnosis.
- Comparison of coding accuracy with previous Canadian and American studies.
Main Results:
- Twenty-one percent (43/209) of charts coded as acute myocardial infarction did not meet diagnostic criteria (false-positives).
- Common reasons for false-positive coding included prior myocardial infarction with procedures and unproven/disproven suspected cases.
- The false-positive rate was lower than some US tertiary hospitals but higher than Boston community hospitals.
Conclusions:
- Significant inaccuracies exist in the coding of acute myocardial infarction, impacting data reliability.
- The findings support the need for revisions to ICD-9-CM codes and coding practices for acute myocardial infarction.
- Improvements in coding are necessary for accurate epidemiological data and healthcare management.
Abstract:
Hospital medical records staff enter diagnostic codes on charts using the International Classification of Diseases (Clinically Modified), Ninth Revision (ICD-9-CM). In a downtown Toronto tertiary hospital, 209 consecutive charts coded for acute myocardial infarction as the primary diagnosis in 1987-88 were reviewed. Criteria for documentation of acute myocardial infarction included symptomatic, electrocardiographic and enzymatic elements. Forty-three (21%) false-positives, ie, charts coded acute myocardial infarction where criteria were not fulfilled, were found (95% confidence interval 15 to 26%). Physician diagnosis of acute myocardial infarction appeared on the face sheet of 30 of the false-positive cases. Common reasons for false-positive face sheet entries and chart coding were acute myocardial infarction within the previous eight weeks with transfer or readmission for coronary angiography and other procedures; and presumed acute myocardial infarction on admission subsequently unproven or disproved. The false-positive proportion was similar to a Canadian study drawing on charts from hospitals of various sizes in 1977, lower than in recent reports from various American tertiary teaching hospitals (P less than 0.0001), and higher than in five Boston area community hospitals (P = 0.0005) where procedure-related transfers or readmissions of previous acute myocardial infarction patients were less likely. This audit lends credence to arguments that changes are needed in ICD-9-CM codes for acute myocardial infarction and in the assignation of reasons for hospitalization.