International Classification of Diseases coding changes lead to profound declines in reported idiopathic pulmonary arterial hypertension mortality and hospitalizations: implications for database studies.
BACKGROUND
Database studies have reported several associations between the diagnosis of idiopathic pulmonary arterial hypertension (IPAH) and mortality attributable to IPAH, including older age, black race, and diabetes.


METHODS
We investigated reported deaths and hospital discharges coded as IPAH and compared these with other forms of pulmonary hypertension. Three databases were used: the US National Center for Health Statistics database (1979-2006), queried for mortality data; the Nationwide Inpatient Sample database (1993-2007), queried for hospital discharge data; and the University of Texas Southwestern Hospital-Zale Lipshy discharge database (1999, 2002).


RESULTS
Marked increases in mortality attributable to IPAH and to pulmonary hypertension (all codes combined) generally were reported from 1979 until 2002 in the National Center for Health Statistics database. In 2003, reported IPAH mortality fell sharply while total pulmonary hypertension deaths increased. The Nationwide Inpatient Sample database showed a similar pattern of changes beginning approximately 2 years earlier. In both cases, the timing of these observations corresponded with changes made to the International Classification of Diseases (ICD) coding system in use for pulmonary hypertension in that particular database. Review of pulmonary hypertension discharge data from the University of Texas Southwestern Hospital-Zale Lipshy showed similar changes in diagnosis code use.


CONCLUSIONS
Sudden shifts in reported IPAH mortality and hospital discharges were seen in all databases, likely related to coding changes. These findings raise questions about the accuracy of pulmonary hypertension diagnosis codes. Studies based on International Classification of Diseases, Ninth Revision and International Classification of Diseases, 10th Revision codes may have inadvertently included patients with other forms of pulmonary hypertension and should be reevaluated in this context. Validation studies of the IPAH diagnosis code are needed, and changes to the ICD coding system should be considered.
Link
Jeffrey
J
Department of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX. Electronic address: Jeffrey.Link@UTSouthwestern.edu.
Glazer
Craig
C
Department of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX.
Torres
Fernando
F
Department of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX.
Chin
Kelly
K
Department of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX.
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D059019:Clinical Coding / Q000639:trends*; D065627:Familial Primary Pulmonary Hypertension; D006753:Hospital Records / Q000706:statistics & numerical data*; D006801:Humans; D006976:Hypertension, Pulmonary / Q000145:classification / Q000453:epidemiology / Q000401:mortality; D007391:International Cooperation; D008875:Middle Aged; D009309:National Center for Health Statistics, U.S.; D010351:Patient Discharge / Q000706:statistics & numerical data; D015995:Prevalence; D035583:Rare Diseases / Q000145:classification* / Q000453:epidemiology / Q000401:mortality*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D016019:Survival Analysis; D013781:Texas; D014481:United States / Q000453:epidemiology