Hospitalization Discharge Diagnoses for Kidney Disease—United States, 1980-2005 FREE

MMWR. 2008;57:309-312

2 figures, 1 table omitted

Kidney disease is the ninth leading cause of death in the United States.¹ Nearly 26 million persons in the United States have chronic kidney disease (CKD), and another 20 million are at increased risk for CKD.² End-stage renal disease (ESRD), which can be caused by either CKD or acute renal failure (ARF), results in approximately 85,000 deaths each year in the United States.³ The total annual cost of treating ESRD in the United States was approximately $33 billion in 2005.³ Much of the care for CKD and ESRD is provided in the outpatient setting; however, the number of hospitalizations for ARF and chronic kidney failure (CKF) is substantial. In 2004, an estimated 221,000 hospitalizations with a first-listed discharge diagnosis of ARF and 19,000 with a first-listed discharge diagnosis of CKF occurred in the United States.⁴ To characterize national trends in kidney disease hospitalizations, CDC analyzed data from the National Hospital Discharge Survey (NHDS) for the period 1980-2005. This report summarizes the results of that analysis, which indicated that (1) numbers and rates of kidney disease hospital discharge diagnoses have increased since the early 1990s, especially among adults aged ≥65 years; (2) a shift has occurred in the type of kidney disease accounting for most of these reported hospitalizations (from CKF to ARF); and (3) an increasing number of kidney disease hospital discharges are associated with a concomitant diagnosis of diabetes mellitus or hypertension. These findings indicate a need for additional research to determine the cause of the increase in ARF discharge diagnoses and to quantify the progression from ARF to CKD and ESRD.

NHDS is conducted annually by CDC to abstract data from medical records from a sample of approximately 500 nonfederal short-stay (i.e., <30 days) hospitals in the 50 states and the District of Columbia.⁴ For this report, kidney disease hospitalizations were classified as those for which kidney disease was listed first through seventh among discharge diagnoses as International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 580-589, which include acute kidney disease, ARF, ESRD, CKF, and other kidney diseases. Hospital discharge records with a diagnosis of kidney disease were further analyzed for any additional diagnoses of diabetes mellitus (ICD-9-CM code 250) or hypertension (codes 401-405). Both age-adjusted and age-specific rates per 10,000 population were calculated by dividing the estimated number of hospitalizations by U.S. Census mid-year estimates of the civilian, noninstitutionalized U.S. population for each year during 1980-2005. The 2000 U.S. standard population was used for direct age standardization of hospital rates for men and women. Race- and ethnicity-specific rates were not calculated because of incomplete reporting of race and ethnicity.

During 1980-2005, approximately 10 million hospitalizations had kidney disease listed as a diagnosis. The annual number of hospitalizations with a recorded diagnosis of kidney disease quadrupled during this period, from approximately 416,000 in 1980 to 1,646,000 in 2005. Age-adjusted hospitalization rates per 10,000 population increased from 20.6 in 1980 to 54.6 in 2005. Kidney disease hospitalization rates were consistently 30%-40% higher among men than among women. The rates for both sexes increased during 1980-2005, from 25.0 to 66.6 per 10,000 population in men and from 17.8 to 45.8 per 10,000 population in women.

In 2005, nearly two thirds (61.4%) of patients hospitalized with kidney disease were aged ≥65 years, compared with 49.9% in 1980. Age-specific hospitalization rates increased in all age groups except persons aged <18 years, but the increase was greatest among persons aged ≥65 years. An increase of approximately 300% (from 56.2 to 179.3 per 10,000 population) occurred among persons aged 65-74 years, and an increase of approximately 350% (from 119.0 to 393.2 per 10,000 population) occurred among persons aged ≥75 years.

Much of the observed change in type of reported kidney disease was the result of consistent increases in the rate of hospitalization for ARF. The age-adjusted rate per 10,000 population for hospitalization for ARF increased from 1.8 in 1980 to 36.5 in 2005, with a smaller increase for CKF (from 7.4 to 13.8 per 10,000 population) during the same period. In 1980, 35.0% of all kidney disease hospitalizations were for CKF, 7.3% were for ARF, and 56.0% were for other kidney disease diagnoses. However, in 2005, 24.3% of these hospitalizations were for CKF, 60.0% were for ARF, and 9.3% were for other kidney disease diagnoses.

Among persons with a reported hospitalization for ARF in 2005, 23.1% had ARF as their first-listed diagnosis, whereas 6.9% had septicemia, 6.4% had congestive heart failure, and 5.9% had acute myocardial infarction as their first-listed diagnosis. In 1980, diabetes mellitus was reported as an additional discharge diagnosis for 23.4% of kidney disease hospitalizations. This proportion peaked at 39.0% in 1996; diabetes was associated with 27.0% of kidney disease hospitalizations in 2005. The proportion of kidney disease hospitalizations with hypertension listed among discharge diagnoses increased from 19.6% in 1980 to 41.1% in 2005.

NT Flowers, JB Croft, Div of Adult and Community Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

During 1980-2005, the rate of hospitalization for kidney disease increased, particularly among adults aged ≥65 years and primarily because of hospitalizations with diagnoses of ARF. The cause of the increase in hospitalizations with ARF diagnoses is unexplained and might be attributed to actual increases in ARF among hospitalized patients or to changes in the way ARF is diagnosed, defined, or reflected in hospital discharge codes. For example, the increase in hospitalization rates for ARF corresponds to the dissemination and implementation of the Kidney Disease Outcomes Quality Initiative guidelines for evaluation, classification, and stratification of CKD, which were issued by the National Kidney Foundation in 2002.⁵ These guidelines identify five stages of CKD: (1) kidney damage with normal or increased glomerular filtration rate (GFR), (2) kidney damage with mild decreased GFR, (3) moderate decreased GFR, (4) severe decreased GFR, and (5) kidney failure. Although the guidelines were intended to help diagnose stages of CKD, the new criteria for kidney dysfunction might have led to increased diagnoses of ARF by causing physicians to make more aggressive attempts at recognizing and managing kidney disease and impaired kidney function. The increased number of hospitalizations for ARF also might be attributable, in part, to the aging of the U.S. population, with greater numbers of older adults having diabetes and hypertension, both of which are major risk factors and comorbidities for kidney disease.⁶

The findings in this report are subject to at least four limitations. First, NHDS data are based on medical records, and determining the accuracy of physician or administrative reporting or the validity of ICD-9-CM classifications was not possible, especially for the diagnosis of ARF, for which no standardized diagnostic criterion exists.⁷ Second, data for certain patients might have been captured on multiple occasions because the survey counted hospital discharges and not individual patients. Third, NHDS data are based on a sample population and therefore are subject to sampling variability. Finally, although racial/ethnic disparities have been observed in the prevalence and treatment of kidney disease,⁸ NHDS data do not allow for analysis of kidney disease hospitalization rates by race or ethnicity because of incomplete reporting of patient race/ethnicity on hospital records.

Despite these limitations, the findings in this report are consistent with other epidemiologic evidence that (1) kidney disease prevalence has increased in the United States since the 1980s,⁹ (2) hospitalizations for ARF are more common among older adults,⁶ and (3) kidney disease hospitalizations are associated with a high prevalence of diabetes and hypertension.⁶ The increasing number of hospitalizations for kidney disease in the United States underscores the need for continued efforts in the early detection of kidney disease through screening programs that can slow or eliminate disease progression. The causes of ARF vary and include infections, toxins, acute organ system dysfunction, surgery, and dehydration. In addition, many cases of ARF are acquired during hospitalizations for other conditions.

A broad effort is needed to encourage health professionals to standardize the criteria for diagnosing ARF. Although the aging of the U.S. population and the change in diagnostic criteria for CKD might partially explain the increase in discharge diagnoses for ARF, the findings in this report also indicate a need for research to determine the causes for this increase and to further quantify the risk for CKD and ESRD associated with ARF.

The findings in this report are based, in part, on contributions by L Agodoa, MD, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.