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Open Access Open Badges Research article

Sensitivity of International Classification of Diseases codes for hyponatremia among commercially insured outpatients in the United States

Alisa M Shea1, Lesley H Curtis13*, Lynda A Szczech24 and Kevin A Schulman13

Author Affiliations

1 Center for Clinical and Genetic Economics, Duke Clinical Research Institute, PO Box 17969, Durham, North Carolina, USA

2 Duke Clinical Research Institute, Durham, North Carolina, USA

3 Division of General Internal Medicine, Department of Medicine, Duke University School of Medicine, Durham, North Carolina, USA

4 Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina, USA

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BMC Nephrology 2008, 9:5  doi:10.1186/1471-2369-9-5

Published: 18 June 2008



Administrative claims are a rich source of information for epidemiological and health services research; however, the ability to accurately capture specific diseases or complications using claims data has been debated. In this study, the authors examined the validity of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis codes for the identification of hyponatremia in an outpatient managed care population.


We analyzed outpatient laboratory and professional claims for patients aged 18 years and older in the National Managed Care Benchmark Database from Integrated Healthcare Information Services. We obtained all claims for outpatient serum sodium laboratory tests performed in 2004 and 2005, and all outpatient professional claims with a primary or secondary ICD-9-CM diagnosis code of hyponatremia (276.1).


A total of 40,668 outpatient serum sodium laboratory results were identified as hyponatremic (serum sodium < 136 mmol/L). The sensitivity of ICD-9-CM codes for hyponatremia in outpatient professional claims within 15 days before or after the laboratory date was 3.5%. Even for severe cases (serum sodium ≤ 125 mmol/L), sensitivity was < 30%. Specificity was > 99% for all cutoff points.


ICD-9-CM codes in administrative data are insufficient to identify hyponatremia in an outpatient population.