International Classification of Diseases coding changes lead to profound declines in reported idiopathic pulmonary arterial hypertension mortality and hospitalizations: implications for database studies

Abstract

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.

Figure 1.

Mortality from PH (death certificates), 1979 to 2005. The sudden decline in reported idiopathic PAH (IPAH) mortality in 2003 appears to relate to the addition of the new International Classification of Diseases, 10th Revision (ICD-10) code “other secondary PH.” * = updated PH classification system was published in 1988; † = ICD-10 was introduced in 1999; PAH = pulmonary arterial hypertension; PH = pulmonary hypertension.

Figure 2.

Mortality rate for IPAH by age group. The greatest increase in IPAH mortality occurred in patients aged > 65 years. See Figure 1 legend for expansion of abbreviation.

Figure 3.

Hospital discharges by year, 1993 to 2007. The fall in IPAH diagnoses in 2001 corresponded with a change in the ICD-9-Clinical Modification index in 2001. See Figure 1 legend for expansion of abbreviations.

Figure 4.

PCWP among patients with unexplained PH at a referral center. Older patients with otherwise unexplained PH after a noninvasive work-up are more likely to have an elevated wedge pressure at the time of cardiac catheterization compared with younger patients. Republished with permission of American College of Chest Physicians. PCWP = pulmonary capillary wedge pressure. See Figure 1 legend for expansion of other abbreviation.