We aimed to examine the trend in the prevalence of hospitalization attributable to hypertensive disease and its subtypes among United States adults aged ≥35 years from 1980 to 2007. Data (n = 4,598,488,000 hospitalized cases) from the National Hospital Discharge Surveys were used to examine the trends of hospitalized patients with first (the reason for admission) and patients with any second to seventh (a co-morbid condition when admission) diagnosis of hypertensive disease (International Classification of Disease, 9th Revision, Clinical Modification: 401 to 405) by gender and geographic region. Age-adjusted rates of disease were calculated using the United States 2000 standard population. The results show that age-adjusted hospitalization rates due to first diagnosis of hypertensive disease increased from 1.74% to 2.06% in men (p <0.01), and from 2.0% to 2.09% in women (p = 0.06) from 1980 to 1981 to 2006 to 2007. Age-adjusted rates due to any second to seventh diagnosis of hypertensive disease significantly increased from 7.06% to 35.09% in men (p <0.001), and from 7.88% to 31.98% (p <0.001) in women from 1980 to 1981 to 2006 to 2007. Patients with second to seventh diagnosis of essential hypertension and hypertensive chronic kidney disease had the highest and the second highest annual percent increases. Subjects living in the Southern region of the United States had the highest prevalence of hospitalization due to any second to seventh diagnosis of hypertensive disease compared with all other regions in 2006 to 2007. In conclusion, the prevalence of hospitalization due to hypertensive disease significantly increased in the United States from 1980 to 2007.
Hypertension (or high blood pressure) is the most important cardiovascular risk factor worldwide, contributing to 1/2 of coronary heart disease cases and approximately 2/3 of the cerebrovascular disease burden. In the United States, about 1 in 3 adults, an estimated 68 million people, have hypertension. Although several studies have examined trends in the prevalence of hypertension using community-based population samples, no studies have been conducted to examine the long-term trends of hospitalization attributable to hypertensive disease, including hypertension and its subtype diseases defined by the International Classification of Disease. Because of the limited resources available for hospitalization support and increasing healthcare costs, recognizing these trends and targeting interventions has become necessary. In the present study, we aimed to quantify and document these trends in hospitalization due to hypertensive disease and subtypes of hypertensive diseases among United States adults in the past 28 years. We hypothesized that there were significant increasing trends in hospitalization rates in patients with first (the reason for admission) and those with second to seventh (a co-morbid condition when admission) diagnosis of hypertensive disease. To test this hypothesis, we used data from nationally representative samples of the United States National Hospital Discharge Surveys (NHDS) from 1980 to 2007.
Methods
The NHDS is conducted by the National Center for Health Statistics (NCHS). Details of the NHDS have been described elsewhere. Briefly, the NHDS provides national estimates of hospital use on the basis of data from patients discharged from noninstitutional hospitals (exclusive of federal, military, and Veterans Administration hospitals) located in the 50 States and District of Columbia. Only short-stay hospitals (average length of stay of <30 days for all patients) or general (medical or surgical) hospitals are included in the surveys. Each year, the sample of hospital discharge diagnosis records represents approximately 1% of all inpatient hospitalizations across 4 regions (Northeast, Midwest, South, and West) in the United States. The sampling design assigns a discharge weight to each hospital record. The discharge weight is the number of hospitalizations that the hospital record represents. Use of these weights permits calculations of nationally representative numbers of hospitalizations. Information collected from hospital records includes date of birth, gender, race, date of discharge, length of stay (i.e., hospitalization), discharge status, and ≤7 discharge diagnoses (i.e., first to seventh—listed). In the NHDS, the first diagnosis of a disease indicates the principal cause of hospitalization, and any second to seventh diagnosis of a disease indicates a co-morbid condition. All conditions are coded according to the International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM). In the study, we tested all subtypes of hypertensive disease coded by ICD-9-CM (401 to 405), because they have a direct and/or an indirect effect on the risk of cardiovascular disease. The subtypes of hypertensive disease include (1) essential hypertension (ICD-9-CM: 401), (2) hypertensive heart disease (ICD-9-CM: 402), (3) hypertensive chronic kidney disease (CKD, ICD-9-CM: 403), (4) hypertensive heart and CKD (ICD-9-CM: 404), and (5) secondary hypertension (ICD-9-CM: 405). We examined the subtypes of hypertensive disease, as we wanted to test which subtype disease strongly contributed to the overall changes of the trends in hypertensive disease. All information collected in the NHDS is held in the strictest confidence according to law. The NCHS Research Ethics Review Board has reviewed and approved the NHDS protocol. Data used in the present analysis are de-identified for personal identifications and obtained following the criteria of Centers for Disease Control and Prevention’s NCHS for the public use.
A serial analysis was conducted to test the study hypothesis. In the first-group data analyses, we estimated the crude and age-standardized hospitalization rates due to hypertensive disease from 1980 to 2007 for men and women separately. The age standardization was done using the direct method with the United States 2000 standard population. The trends were examined for those with first and any second to seventh diagnosis of hypertensive disease. Changes in age-standardization rates of hypertensive disease are depicted using log-scale figures, and differences in the rates by region are depicted using the Geographic Information System.
In the third-group data analysis, trends of hypertensive disease from 1980 to 2007 were tested using the formula: У i = a + βχ i , in which У i is the natural logarithm of the rates and χ i is calendar years. The estimated percentage change was computed using 100 × (e β −1).
In the fourth-group data analyses, we applied multivariate logistic regression analysis technique to estimate odds ratios of risk factors for hospitalizations due to first and any second to seventh diagnosis of hypertensive disease. These risk factors included age (per 10 years), gender (men vs women), regions (Northeast, Midwest, South, and West), and survey periods (1990 to 1999 and 2000 to 2007 vs 1980 to 1989).
In the study, we did not analyze racial or ethnical differences because >10% to 20% of patients had missing data on race or ethnicity in the NHDS.
All data analyses were performed using SAS software version 9.2 (SAS Institute Inc., Cary, North Carolina, 2010). SAS survey procedures that take into account the complex sample design of the NHDS were used.
Results
Table 1 lists the significant differences in mean age and prevalence of hospitalized patients with first and any second to seventh diagnosis of hypertensive disease, except for women and those living in the Midwest region of the United States with the first diagnosis of hypertensive disease from 1980 to 1981 to 2006 to 2007.
| Variable | With First Diagnosis of Hypertensive Disease | With Any Second to Seventh Diagnosis of Hypertensive Disease | ||||
|---|---|---|---|---|---|---|
| 1980–1981 (n = 4,811) | 2006–2007 (n = 9,625) | p | 1980–1981 (n = 22,516) | 2006–2007 (n = 191,943) | p | |
| M/R (SEM/P) | M/R (SEM/P) | M/R (SEM/P) | M/R (SEM/P) | |||
| Age (SEM) | 63.0 (0.22) | 63.8 (0.29) | 0.03 | 66.0 (0.10) | 68.3 (0.06) | <0.001 |
| Men | 1.72 (0.04) | 1.88 (0.06) | 0.03 | 8.05 (0.09) | 40.17 (0.20) | <0.001 |
| Women | 2.24 (0.05) | 2.16 (0.05) | 0.24 | 9.94 (0.09) | 39.95 (0.18) | <0.001 |
| Region (SEP) | ||||||
| West | 1.55 (0.08) | 2.02 (0.10) | <0.001 | 7.88 (0.16) | 37.20 (0.32) | <0.001 |
| Northeast | 1.65 (0.06) | 2.26 (0.08) | <0.001 | 9.72 (0.13) | 40.05 (0.25) | <0.001 |
| Midwest | 1.88 (0.06) | 1.79 (0.07) | 0.38 | 9.47 (0.12) | 40.69 (0.29) | <0.001 |
| South | 2.58 (0.06) | 2.06 (0.07) | <0.001 | 9.00 (0.11) | 41.00 (0.22) | <0.001 |
Age-adjusted prevalence rates of hypertensive disease with first diagnosis increased from 1.74% in 1980 to 1981 to 2.06% in 2006 to 2007 in men (p = 0.003), and from 2.00% to 2.09% in women (p = 0.06) during the same period. The age-adjusted prevalence for those with any second to seventh diagnosis of hypertensive disease increased from 7.06% in 1980 to 1981 to 35.09% in 2006 to 2007 in men (p <0.001) and from 7.88% to 31.98% in women (p <0.001) during the same period. Figure 1 depicts the trend in log values that among those with any second to seventh diagnosis, essential hypertension, hypertensive CKD, and hypertensive heart and CKD dramatically increased from 1980 to 1981 to 2006 to 2007 in men and women.
The annual percent increase in the rate of those with the first diagnosis of hypertensive disease was 1.44% in men (test for trend, p = 0.003) and 0.96% in women (p = 0.06; Table 2 ). The annual percent increase in those with any second to seventh diagnosis of hypertensive disease was 6.44% in men (p <0.001) and 5.64% in women (p <0.001). Subtypes essential hypertension and hypertensive CKD were the top 2 contributors to the increasing trends in both genders.
| Variable | Changes from 1980 to 2007 | p | |
|---|---|---|---|
| Regression Coefficient | Estimated Annual % Change | ||
| b (SE) | Rate (SE) | ||
| With first diagnosis of hypertensive disease | |||
| Men: total hypertensive disease | 0.014 (0.004) | 1.44 (0.38) | 0.003 |
| Women: total hypertensive disease | 0.010 (0.005) | 0.96 (0.46) | 0.06 |
| With any second to seventh diagnosis of hypertensive disease | |||
| Men | |||
| Total hypertensive disease | 0.062 (0.002) | 6.44 (0.21) | <0.001 |
| Subtypes of hypertensive disease | |||
| E-HT | 0.057 (0.002) | 5.90 (0.24) | <0.001 |
| HT-HD | −0.013 (0.003) | −1.26 (0.33) | 0.002 |
| HT-CKD | 0.054 (0.003) | 5.54 (0.30) | <0.001 |
| HT-HD-CKD | 0.009 (0.001) | 0.94 (0.11) | <0.001 |
| S-HD | −0.020 (0.017) | −2.00 (1.76) | 0.27 |
| Women | |||
| Total hypertensive disease | 0.055 (0.002) | 5.64 (0.19) | <0.001 |
| Subtypes of hypertensive disease | |||
| E-HT | 0.052 (0.002) | 5.32 (0.21) | <0.001 |
| HT-HD | −0.025 (0.004) | −2.46 (0.41) | <0.001 |
| HT-CKD | 0.040 (0.002) | 4.13 (0.24) | <0.001 |
| HT-HD-CKD | 0.007 (0.001) | 0.66 (0.10) | <0.001 |
| S-HT | 0.002 (0.016) | 0.19 (1.62) | 0.91 |
Figure 2 depicts the increasing trends in age-adjusted prevalence of hypertensive disease with any second to seventh diagnosis in 4 regions of the country. Subjects living in the Western region had the lowest prevalence of hypertensive disease in both men and women, and subjects living in the South had the highest prevalence in men (36.68%) and women (34.23%) in 2006 to 2007. Similar geographic variations, with the highest rates in the South, were observed in patients with the first diagnosis of hypertensive disease (data not shown).
