Annual Data Report Chapter IX Key Words: Admissions in ESRD hospitalization Dialysis hospitalization Standardized hospitalization ratio Geographic variation in hospitalization Length of stay H ospitalization rates reflect many aspects of ESRD therapy. Among the most important are the frequency and duration of reported hospitalizations, both of which are significantly affected by the level of patient morbidity. Unfortunately, other influential (but unrelated) factors include the health insurance system and individual patient needs. Consequently, hospitalization data are subject to numerous sources of variability, and tend to be imperfectly reported at both patient and aggregate levels. Despite these faults, such data allow the USRDS to provide reasonably objective characterizations of the morbidity experience in the ESRD population. The source of hospitalization data for this chapter is Medicare billing records obtained from the HCFA standard analysis files (SAF; see Chapters I and XIII) for the years 1993-1996. The majority of analyses presented here will be based on 1994-1996 data only; 1993 data are only used in an empirical investigation of time trends. The 1997 Annual Data Report (ADR) included hospitalization data from 1991 and 1992. Data from these years are no longer included because the group of patients used for this report has been substantially narrowed to include only patients with more complete Medicare billing data, compared to those included in the 1997 ADR. In particular, data used in these analyses and in the hospitalization reference tables (Section H) are now limited to patients whose start date for each year (January 1 or day 91 of ESRD) falls in between the start and end dates, based upon Medicare payment activity, used for the cost studies in this ADR. These data are currently available only for 1993-1996. The specific rationale for this change is described in the Gold Pages (Section K, (i)-(iv)). In short, using an individual s Medicare cost profile to determine eligibility for inclusion in the analysis of hospitalization increases the likelihood of capturing all available information on hospitalization. is a major component of these costs, and patients for whom Medicare is the secondary payer for all or part of the study period are automatically excluded from the analysis because the Medicare bills are unlikely to include all hospitalizations for such patients. It was determined by the USRDS that the eligibility criteria used in previous years did not adequately screen patients for whom Medicare was the secondary payer and consequently a number of such patients (particularly in the later years) contributed relatively sparse information on hospitalization. The failure to capture these events and/or days in the hospital may have biased (perhaps even differentially by age) the various rates we computed towards zero. The new criteria should lead to summary rates that better reflect the true hospitalization experience of ESRD patients. The remainder of this chapter is organized as follows. First, the specific patient eligibility criteria used to select patients for the analyss of this chapter are summarized. Second, the hospitalization experience of incident and prevalent dialysis patients is summarized via total hospital admissions and hospital days. These analyses are done on a per calendar year basis, and consequently do not adjust for the fact that members of the study cohort are at risk for hospitalization for differing periods of time. 121
Annual Data Report We then summarize the hospitalization rates of incident and prevalent dialysis patients, defined as the total number of admissions per year at risk for hospitalization. The analyses in the last part of this chapter utilize a comparison measure based on standardized first hospital admission rates (Strawderman), which is an adaptation of the standardized mortality ratio (SMR) methodology (1997 ADR, Chapters V and XIII). Using these standardized rates, we compare the standardized hospitalization ratio (SHR) for dialysis patients across states for 1994-1996 and also investigate time trends in hospitalization for 1993-1996. Finally, summaries by age, race, sex, diabetic status, and modality group are given in the reference tables (Section H), and apply to data collected between 1994-1996. New additions to the 1998 ADR compared to the 1997 ADR include: SHRs by state for the period 1994-1996 are given in Table H.2, and reference tables for 3 year (1994-1996) and 1 year (1996) summaries of total hospital admissions by diagnosis (DRG) code may respectively be found in Tables H. and H.6. Patient Eligibility To summarize the criteria, note first that any patient having Medicare as a secondary payer has been excluded. This excludes approximately 8 percent of patients with Medicare payments for the period 1993-1996. The reason for this exclusion is that our primary data source (i.e. Medicare bills) only provides an incomplete record of medical care episodes for these patients. The goal of these new criteria is, as with past ADRs, to ensure that complete Medicare payment data (and hence information on hospitalizations) are available for patients in these analyses. The study start date for each of the patients included in any of the analyses in this chapter is 3 days after the latest of (i) January 1, 1992; (ii) first ESRD service date; (iii) Medicare Part B entitlement date; or (iv) the first month in which the dialysis bills for that patient exceed $67. Prevalent patients have their eligibility determined as of January 1; any previously transplanted patient currently on dialysis whose transplant failed within 6 days prior to January 1 is excluded. The latter is done under the presumption that such patients may contribute hospitalizations early during the followup period that are due to the transplant failure and not dialysisrelated complications. Patients who start followup or die during a year are considered to be at risk for only a portion of the year, and eligible patients who are transplanted during a given year have their at-risk period censored 3 days prior to the date of transplantation. Finally, patients who switch modalities during the year are assigned to the new modality at the start of the next year. As discussed earlier, all patients who die of AIDS are excluded retroactively at death. 1 1 Average Number of Hospital Admissions and Days per Year for Dialysis Patients, 1993-1996 Hospital Days 12.7 Hospital Days 12.2 11.8 Hospital Admissions 11.3 3 2 1.4 Hospital Admissions 1.47 1.49 1.47 1 * 1996 data preliminary 1993 1994 199 1996 * Year Figure IX-1 IX-1 Average number of hospital admissions and days in hospital by year for 1993-1996 for Medicare dialysis patients. Median number of hospital admissions is 1 for each year and the median number of days spent in the hospital is 4 for 1993-199 and 3 for 1996. Patients who died of AIDS are excluded. Source: Special Analysis 122
Annual Data Report Trends in Both the yearly number of hospital admissions and days per patient are important measures in the study of hospitalization in dialysis patients. Figure IX-1 describes the average number of hospital admissions and average days in the hospital per patient for each of the years 1993-1996. Figures IX-2 and IX-3 describe the distribution of patients having a given number of hospital admissions and total days in the hospital for patients prevalent on January 1 or incident during 1996, by patient age under or over 6. Note that each of these figures is based on the number of events per calendar year rather than the number per year at risk. Since the time at risk is much less than 1 year for many patients, the number of hospital admissions and days per year at risk (e.g., as seen in Table H.3) are greater than the numbers shown here. In Figure IX-1, we see a very slight increase in the average number of admissions for the period 1993-1996. This is in contrast to the slight decrease reported in the 1997 ADR for the period 1992-199. Days in the hospital per year are seen to have decreased approximately 11 percent between 1993 and 1996; this drop is somewhat smaller than the 17 percent decrease reported in the 1997 ADR. The eligibility criteria used in the 1997 ADR included more patients with incomplete Medicare billing records in recent years than in years before 1994. This inclusion led to averages that were too low in recent years in the 1997 ADR. From Figures IX-2 and IX-3, it is seen that the majority of patients have a small number of both admissions and total hospital days per year. However, both of these distributions have a long tail extending to the right, and the distribution of days is skewed more than total admissions. More patients have zero admissions and zero days than any other number. A nearly identical pattern was observed in the 1997 ADR. Figure IX-2 shows that approximately 8 (78) percent of the patients in the 6+ (under 6) age groups had fewer than 3 hospital admissions, while 97 (9) percent respectively had or fewer. The median number of admissions is 1 per year in both groups, while the mean number of admissions in the older and younger age groups are 1.4 and 1. respectively. These results are similar to those reported in the 1997 ADR, although the mean number of admissions is slightly higher than previously reported. Again, this increase is expected due to the new eligibility criteria. In terms of hospital days, we see in Figure IX-3 that 36 percent and 4 percent of the patients in the older and younger age groups did not require hospitalization. In previous ADRs, we reported that in 1993 (199), 34 (39) percent of older patients and Distribution of Medicare Dialysis Patients by Number of Hospital Admissions during 1996*, by Age Percent of Patients 4 41 38 Under 6 Mean=1. Median=1 6 Plus Mean=1.4 Median=1 3 2 1 26 23 16 14 8 9 Figure IX-2 3 3 2 2 1 1 2 1 1 2 3 4 6 7 8+ Hospital Admissions per Calendar Year * 1996 data preliminary IX-2 Percentages of Medicare dialysis patients by number of hospital admissions during 1996 and age. Mean and median are also denoted. Patients who died of AIDS are excluded. This figure shows counts of hospital admissions for the entire year rather than admissions per year at risk. As a result, the numbers here are lower than those for total admissions per year at risk. Source: Special Analysis 123
Annual Data Report Distribution of Medicare Dialysis Patients by Number of Hospital Days during 1996*, by Age Percent of Patients 4 3 4 36 31 31 Under 6 Mean=11.1 Median=3 6 Plus Mean=11.4 Median=4 2 1 12 14 6 7 Figure IX-3 4 4 2 1-1 11-2 21-3 31-4 41- + * 1996 data preliminary Hospital Days per Calendar Year 2 4 IX-3 Percentages of Medicare dialysis patients by total days hospitalized in a single calendar year by age, 1996. Mean and median are also denoted. Patients who died of AIDS are excluded. This figure shows counts of days in the hospital for the entire year rather than days per year at risk. The numbers here are lower than those for days per year at risk. Source: Special Analysis 42 (48) percent of younger patients did not require hospitalization. The reduced fraction of patients with zero admissions, compared to prior ADR reports, is again likely to be due to the change in eligibility criteria rather than to a rise in hospitalization. This is because the number of hospital days per patient was more likely to be underrepresented in the 1997 ADR. Just over 11 percent of both age groups spent 3 or more days in the hospital. In 1996, the median and mean for hospital days were respectively 4 and 11.4 for patients age 6+ and 3 and 11.1 for patients under 6. In 199, the median and mean for hospital days were respectively 3 and 11.4 for patients age 6+ and 1 and 9.6 for patients under 6. The discrepancies again reflect an undercount in previous ADRs, particularly among younger patients. In general, the trends observed here are similar to those reported in earlier ADRs. Specifically, younger patients tend to have less hospitalization, measured on either scale, and the distribution of hospital days has decreased over time. The apparent decrease in hospitalization time is consistent with the current overall national trend of decreasing hospitalization, which itself reflects efforts to contain overall health care costs. On the other hand, the relatively stable trend in the number of admissions may itself reflect a fixed medical need of treating ESRD patients. Crude Rates Based on Total Admissions The patient populations under study in Figures IX-1 through IX-3 include prevalent dialysis patients and hence include patients having different lengths of followup. The above descriptive analyses do not account for this, and therefore we computed an aggregated rate per year at risk for hospitalization, defined as the ratio of total hospital admissions or days to the total time at risk. In order to stabilize the estimated rates, we pooled data for the period 1994-1996, calculated yearly totals for the number of hospital admissions and years at risk for hospitalization, and then computed the ratio of admissions to years at risk in order to obtain the overall rate. These rates are computed for various age, race, sex, and modality groups within the ESRD population in order to compare the hospitalization experience among different groups of patients hospitalized over the period 1994-1996. Rates Based on Total Admissions The hospitalization rates summarized in Figures IX-4 through IX-7 depict the experience of the dialysis population by different subgroups and are computed from information found in Table H.3. In 124
Annual Data Report 4. 4. 3. 3. Hospital Admissions per Year at Risk for Medicare ESRD Patients, by Modality and Age, 1994-1996 Admissions / Yr at Risk All Dialysis Hemodialysis CAPD/CCPD All ESRD 2. 2. 1. 1... 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX-4 Figure IX-4 Total hospital admissions per patient year at risk for all Medicare dialysis patients by modality and age, 1996. Patients are grouped by treatment type based on the treatment method they were using on January 1 of the year. Patients who died of AIDS are excluded. Source: Reference Table H.3 contrast to the 1997 ADR, we now report comparisons for rates based both on total admissions and hospital days. For the admissions rates, the years at risk for hospitalization for each patient are determined by subtracting the time actually spent in the hospital from the total time on observation. This calculation explicitly accounts for the fact that patients are not at risk for a new hospitalization while already in the hospital. In counting total admissions, hospitalizations that overlap or occur without any days between discharge and the subsequent admission are combined into a single hospitalization spanning from the admission of the first to the discharge of the last; this reduces the total number of hospitalizations by about 1 percent. This methodology differs from that of some other researchers (HCFA 1994). Rates are also computed for hospital days for various age, race, sex, and modality groups; a summary may be found in Reference Table H.4. A difference between rates based on total days and those based on total admissions is that the at-risk period for the former includes time spent in the hospital since being in the hospital does not preclude one from being at risk for an additional day in the hospital. As discussed in the 1997 ADR, rates based on total admissions and hospital days must be interpreted with some caution. This is particularly true for the standard error tables, which rely heavily upon the assumption that these counts follow a Poisson distribution. It was shown in the 1996 ADR (Figure VIII-3) that the Poisson assumption is unlikely to hold for such data; one reason for this problem may be related to a greater than average risk for future hospitalizations for patients who had more than one admission during the year. Figure IX-4 shows the total admission rates by modality as a function of age. In order to increase the stability of the rates, data are pooled for the periods 1994-1996. As expected, the rates generally increase with age for each treatment modality, the exception being the youngest age groups where hospitalization tends to start high and then initially declines. The rates for all modalities, save CAPD/CCPD, are generally very similar. rates among CAPD/CCPD patients are generally slightly higher than for hemodialysis patients in each age group until age 6, at which point CAPD/CCPD has a lower hospitalization rate. This is consistent with trends reported in the 1996 and 1997 ADRs. It was reported in the 1996 ADR that hospitalization rates for CAPD/CCPD patients have in recent years been steadily falling while those for hemodialysis patients have remained relatively stable. Habach et al (199) reported such comparisons for 1988 through 199. Suggested reasons for reduced hospitalizations among CAPD/CCPD patients included changes in the frequency of switching between modalities and differences in age distributions among the two treatment groups. The differences in hospitalization 12
Annual Data Report Hospital Admissions per Year at Risk for Male Medicare Dialysis Patients by Race and Age, 1994-96 4. Admissions / Yr at Risk 4. 3. 3. White Black Asian Native American 2. 2. 1. 1... 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX- Figure IX- Total hospital admissions per patient year at risk for male Medicare dialysis patients by race and age, 1994-96. Patients who died of AIDS are excluded. Source: Reference Table H.3 reported here and in the 1996 and 1997 ADRs are smaller than those found in Habach et al (199). This is possibly due to improvements in connection devices thereby reducing peritonitis risk or increased outpatient treatments of peritonitis in CAPD/CCPD patients. The fact that there is no significant decrease in the CAPD/CCPD hospitalization rate and in some cases a slight increase over those rates reported in the 1996 ADR perhaps suggests that the rate of hospitalization among CAPD/CCPD patients is beginning to stabilize. Actual differences between rates for CAPD/CCPD and hemodialysis patients might be Hospital Admissions per Year at Risk for Female Medicare Dialysis Patients by Race and Age, 1994-96 4. Admissions / Yr at Risk 4. 3. 3. White Black Asian Native American 2. 2. 1. 1... 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX-6 Figure IX-6 Total hospital admissions per patient year at risk for female Medicare dialysis patients by race and age, 1994-96. Patients who died of AIDS are excluded. Source: Reference Table H.3 126
Annual Data Report Hospital Admissions per Year at Risk for Medicare Dialysis Patients by Diabetes, Sex, and Age, 1994-96 4. Admissions / Yr at Risk 4. 3. 3. Diabetes-female Diabetes-male Nondiabetes-female Nondiabetes-male 2. 2. 1. 1... 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX-7 Figure IX-7 Total hospital admissions per patient year at risk for all Medicare dialysis patients by age, sex, and primary cause of ESRD (diabetes, nondiabetes), 1996. Patients who died of AIDS are excluded. Source: Reference Table H.3 larger than are reported because we have used an intent to treat assignment of dialysis modality. That is, hospitalizations for patients who switch in the middle of the calendar year are not attributed to their new modality until January 1 of the following year. The USRDS has previously shown that CAPD/CCPD patients switch to hemodialysis approximately three times as often as hemodialysis patients switch to CAPD/CCPD (USRDS 199). If hemodialysis patients tend to incur less hospitalizations, reported rates for CAPD/CCPD patients may be biased downward, while rates for hemodialysis patients are 3 3 2 2 Hospital Days per Year at Risk for Male Medicare Dialysis Patients by Race and Age, 1994-96 Days / Yr at Risk White Black Asian Native American 1 1 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX-8 Figure IX-8 Total hospital days per patient year at risk for male Medicare dialysis patients by race and age, 1996. Patients who died of AIDS are excluded. Source: Reference Table H.4 127
Annual Data Report 3 3 2 2 Hospital Days per Year at Risk for Female Medicare Dialysis Patients by Race and Age, 1994-96 Days / Yr at Risk 37 White Black Asian Native American 1 1 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX-9 Figure IX-9 Total hospital days per patient year at risk for female Medicare dialysis patients by race and age, 1994-96. Patients who died of AIDS are excluded. Source: Reference Table H.4 likely to be biased upward (although much less so) if CAPD patients with poorer health are more likely to switch. Figures IX- and IX-6 show the total admission rates and Figures IX-8 and IX-9 show total hospital day rates broken down by age, race, and sex. The overall patterns are very similar whether admissions or total days are considered. The rates for Asians are substantially lower than those for Blacks, Whites, or Native Americans in almost all age groups with the exception of -14 year group. The rates for Blacks 3 Hospital Days per Year at Risk for Medicare Dialysis Patients by Diabetes, Sex, and Age, 1994-96 Days / Yr at Risk 3 2 Diabetes-female Diabetes-male Nondiabetes-female Nondiabetes-male 2 1 1 1-19 2-29 3-39 4-49 -9 6-69 7-79 8+ -14 2-24 3-34 4-44 -4 6-64 7-74 8-84 IX-1 Figure IX-1 Total hospital days per patient year at risk for all Medicare dialysis patients by age, sex, and primary cause of ESRD (diabetes, nondiabetes), 1994-96. Patients who died of AIDS are excluded. Source: Reference Table H.4 128
Annual Data Report tend to be higher than for Whites both early and late in life, with this pattern being somewhat more pronounced for males than for females. Rates among Black females are higher than for White females up to age 4, lower to age 8, and higher after age 8. These results are consistent with those reported in earlier ADRs. It is important to note that the rates for patients aged -19 are, relative to the other age groups, based on rather small sample sizes. This is especially true for Asians and Native Americans, and to a lesser extent Blacks and Whites. Consequently, small changes in either the number of admissions or time at risk may result in large changes in the calculated rates, and the extreme patterns observed in these groups over short time periods may simply be due to rate instability rather than any real difference. Furthermore, the rates for the youngest age group are also likely to be affected by patient selection: Given the high transplantation rate in this group, those who have never been transplanted are likely to be less healthy and hence have higher hospitalization rates. Interesting but largely expected differences are observed when one considers hospital admission rates broken down by diabetes status, described in Figure IX-7. Female diabetics have a uniformly higher rate of hospital admissions than any other group, followed by diabetic males, nondiabetic females, and finally nondiabetic males. It is interesting to observe rather substantial gender differences within the diabetic group for the ages 2-24. The substantial spike in the female diabetic rate may be at least partially attributable to the presence of high-risk pregnancies in that group. The patterns for hospital days (see Figure IX-1) are quite similar. Rates are not provided by diabetic status for patients younger than 2 since the number of patients in this group for which diabetes is considered the cause of ESRD is extremely small. Standardized Ratio (SHR) Methods The standardized mortality ratio (SMR) is a ratio of the observed number of deaths for a given patient study group divided by expected number of deaths for that patient study group based on national death rates. Wolfe et al (1992) use the published USRDS national ESRD mortality rates given in deaths-per-patient-year by age, race, and diagnosis group. The USRDS has since updated this methodology and now uses a more sophisticated model-based procedure to compute ESRD mortality rates at the national level. A more precise description of the methodology is given in Chapter XIII. These national ESRD mortality rates can then be used, for example, to compare mortality rates among dialysis facilities with different patient mix characteristics by simply computing the ratio of the observed number of deaths to the expected number within each group, the latter being adjusted for differences in age, race, and diagnosis. The expected number of deaths within a group is determined by multiplying the total patient-years observed within each age-race-diagnosis category by the corresponding national rate, and then summing over all of the categories. An observed SMR larger (smaller) than 1. denotes potentially a higher (lower) mortality rate than the national ESRD norm. The SMR is subject to random variation, however, and thus should be interpreted cautiously and not without some evaluation of statistical significance. Further discussion of such matters can be found in Wolfe et al (1992) and also Wolfe (1994). The USRDS produces national ESRD hospitalization rates in a similar manner to the mortality rates. Hence, for patients eligible under the aforementioned eligibility criteria, we can calculate a standardized hospitalization ratio (SHR) using the rates in Table H.1. In calculating the SHR, we restrict our attention to the first hospitalization event for each individual. That is, within a given year, only the first hospitalization event for an individual is counted. Accordingly, the risk time for that individual is defined as the days from entry until a first hospitalization, a censoring event, or December 31 occurs. Censoring events are death and transplant; a patient s risk period is truncated 3 days prior to transplant in order to avoid attributing the transplantrelated hospitalization to the observed count. National first hospitalization rates are obtained for 248 patient subgroups defined by age (16 groups), race (4 groups), sex (2 groups), and diabetes (2 groups) in an essentially identical manner to the SMR In short, a log-linear Poisson regression model is used to smooth the observed national first hospitalization rates; the resulting rates represent weighted averages of the observed and model-predicted rates, with the observed rate being weighted more heavily for larger patient subgroups. The advantage of this approach is that the observed rates in some patient subgroups are rather variable from year to year due to small numbers of patients; taking a weighted average with the model-predicted rate stabilizes (i.e., reduces the 129
Annual Data Report variability of) the resulting rate across time (see Chapter XIII for in-depth discussion).. The rationale for considering only the first hospitalization event is explained in detail in Strawderman et al (see Chapter IX of the 1997 ADR for a summary). As pointed out in Strawderman et al, the SHR reflects the useful information found in an appropriately defined standardized total admissions rate (STAR). For example, at the dialysis facility level, a low SHR necessarily indicates a low overall admissions rate; obviously, if there are few first admissions, there can be few total admissions (unless a few patients at the facility have particularly chronic hospitalization patterns). Correspondingly, a high SHR indicates that many more patients at the facility are entering the hospital than at the national level. Compared to the STAR, the SHR is also less sensitive to the level of comorbidity at the patient level, and more sensitive to the scope (or distribution) of comorbidity at the facility. From the point of view of facility evaluation, the latter seems more relevant. Finally, in view of the fact that approximately 64 percent of the patients had 1 or fewer admissions (see Figure IX-1), the results of the analyses to be presented will be similar to any proper analysis of standardized rates based on total admissions. To obtain the SHR for a specific dialysis unit in a specific year, the total number of first hospital admissions for each eligible patient treated during that time period is divided by the expected number of first hospitalizations. The expected number of first hospitalizations is calculated similarly to the expected number of deaths used in calculating the SMR. Specifically, the observed patient-years at risk for hospitalization in that unit is sub-divided by age, race, sex, and diagnosis, multiplied by the corresponding national rate for those groups, and then summed up over all groups to obtain the total expected number of first hospitalizations in that unit for that year. This produces standardized first hospitalization rates, adjusted for age, race, sex, and diagnosis, that share a similar interpretation to the adjusted SMR. That is, values of the SHR larger than 1. indicate first hospitalization rates above the national norm while values below 1. denote lower rates. Analyses by State The SHRs computed for the analyses of this section are based on data obtained for 1994-1996. Standardized Ratios by State (quartiles), Medicare Dialysis Patients Only, 1994-96 NH + ME + VT WA OR CA + HI SHR > 1.8 SHR 1.1-1.7 SHR.94-1. SHR <.93 MT + ID + WY + NV + AK UT AZ CO NM ND + SD NE KS OK TX MN IA MO AR LA MS WI IL TN AL IN MI KY OH GA FL PA + DE WV SC NC VA NY NJ MD DC CT IX- 11 MA RI Figure IX-11 Standardized First Ratios for Medicare dialysis patients by state, 1994-96. Small states are grouped together as indicated in the reference table. Rates are adjusted for age, race (Black, White, Asian, Native American), sex, and diagnosis (diabetic, other). Patients with missing or unknown race, or missing primary diagnosis are excluded. Patients who died of AIDS are excluded. Source: Reference Table H.2 13
Annual Data Report Rates are adjusted for age, race, sex, and diagnosis. Small states are grouped together as indicated in Table H.2. Figure IX-11 summarizes the distribution of SHRs for dialysis patients computed on a state-by-state basis, subject to the grouping described above. This differs from the 1997 ADR, where rates were computed at the dialysis facility level by census region, and provides more localized information. States are shaded according to whether the state- or region-specific SHR is in the first (SHR =.93), second (.93 < SHR = 1.), third (1. < SHR = 1.7), or fourth (SHR > 1.7) quartiles. The higher SHRs tend to be concentrated in eastern and southern United States, as has been reported in previous years. It was shown in the 1997 ADR that there was variability in the SHR by both size and geographic (i.e., census) region. To a large extent the same patterns are reflected here. The relatively high rate for the West South Central Region reported in the 1997 ADR can be seen to be largely driven by the first hospitalization rates in Louisiana (1.19), Arkansas (1.19), and Oklahoma (1.7), whereas Texas is just below the national average (.97). A similar statement can be made for the Middle Atlantic States (Pennsylvania, Delaware, and New Jersey all have high rates relative to New York), the East South Central Region (Kentucky, Alabama, and Tennessee) and the South Atlantic Region (West Virginia, Georgia, Maryland, and Washington D.C.). It is unclear which factors are primarily responsible for the geographic variation observed here; several major patient mix characteristics have been adjusted for, but other factors which have not been adjusted for may also be important. These trends are consistent with trends observed in studies of non-esrd patients (Gornick, 1982) as well as past studies of hospitalization among ESRD patients (USRDS 1991, 199, 1996, 1997). We note that Figure V-9 (Chapter V), which gives the SMR by state for dialysis patients, shows a rather similar pattern to the SHR. In particular, many (but not all) of the states that have relatively high (low) hospitalization rates also have relatively high (low) mortality rates. Two states (Missouri and South Carolina) have relatively low hospitalization rates but mortality above the national average. Of the six possible combinations (high, average, or low mortality versus high, average, or low hospitalization) that can occur, this one is evidently the most suggestive. However, it is important to remember that these results are merely associations suggested by the data and alone do not necessarily provide evidence of a causal relationship 1.1 1. National SHRs of First Admissions by Year with 9% Confidence Intervals, Medicare 1993-1996 SHR* 1.4 1.3 1.3 1..9 REF..8 1993 1994 199 1996 ** SHR* First Admissions * relative to 1996 first hospital admission rates ** 1996 data preliminary Figure IX-12 IX-12 Standardized first hospital admissions ratio for Medicare dialysis patients over time, 1993-1996. Ratios are standardized by sex, race, age, and cause of ESRD (diabetes, nondiabetes). Ratios are calculated by summing all observed first hospitalizations for each year and dividing them by the respective sum of expected first admissions. Ninety-five percent confidence intervals are indicated for 1993-199; but not for 1996 since rates are standardized to 1996. Patients who died of AIDS are excluded. Source: Special Analysis 131
Annual Data Report between low hospitalization and increased mortality. Further information not currently being taken into account would be needed before such a determination could be justified. Time Trends in the SHR The results in Figure IX-12 indicate that dialysis patients are experiencing less hospitalization overall with each passing year, with approximately a 4 percent drop in (first) admissions between 1993 and 1996. This is considerably lower than the 13 percent drop reported last year, and likely reflects the change in patient eligibility criteria. It was mentioned earlier that the incomplete information on patients with Medicare as secondary payer was more problematic in later years; the fact that the hospitalization rates are relatively similar reflects this fact. The fact that the 9 percent confidence intervals overlap each other indicate that although the SHRs are decreasing through time, they are not pairwise statistically significantly different from one another. However, the SHRs for each of the 3 years (1993-199) is statistically significantly different than the 1996 SHR. Results presented earlier indicate that this drop in hospitalization is complemented by an approximately 11 percent reduction in the average number of days per admission each year. These reported decreases in hospitalization over the 1993-96 period are not very striking. Chapter X of the 1997 ADR provides some estimates of the spending for inpatient care for both dialysis and transplant patients. Medicare spending for inpatient care in 199 increased by 6 percent per patient year at risk as compared to the average of the 1991-94 period. If the two indicators of hospitalization (SHRs reported in this Chapter and the spending per patient year at risk for inpatient care reported in Chapter X of the 1997 ADR) are consistent then the spending per hospitalization episode must be increasing. Such phenomena would be consistent with a process of more severe cases being treated as an inpatient as less severe cases are shifted to the outpatient setting. Analyses of this topic are worthy of additional research that are beyond the scope of this current report. Nonetheless the substantial decreases in rates of hospitalization reported above are most intriguing and should be considered good news. Until these findings can be reproduced with either independent data from outside the Medicare system, or with independent data within the Medicare system (e.g. physician payments), caution in the interpretation of these trends in SHRs would be prudent. References End-Stage Renal Disease Research Report 1992. U.S. Department of Health and Human Services; Health Care Financing Administration; Bureau of Data Management and Strategy. September 1994. Gornick M. Trends and regional variations in hospital use under Medicare. in: Rothberg DL (ed). Heath and Co., Lexington MA. 1982, pp. 131-184. Habach G, Port FK, Mauger E, Wolfe RA, Bloembergen WE. among US dialysis patients: Hemodialysis versus peritoneal dialysis. J Am Soc Nephrol 199; :194-1948. Port FK, Held PJ, Nolph KD, Turenne MN, Wolfe RA. Risk of peritonitis and technique failure by CAPD connection technique: a national study. Kidney Int 1992, 42: 967-974. Strawderman RL, Levine G, Hirth RA, Port FK, Held, PJ. Using USRDS generated hospitalization tables to compare facility-specific ESRD hospitalization rates to national rates. Kidney Int 1996; : 71-78. United States Renal Data System. USRDS 1991 Annual Data Report. National Institutes of Health, National Institutes of Diabetes and Digestive and Kidney Diseases. Bethesda, MD, 1991. United States Renal Data System. USRDS 199 Annual Data Report. National Institutes of Health, National Institutes of Diabetes and Digestive and Kidney Diseases. Bethesda, MD, 199. United States Renal Data System. USRDS 1996 Annual Data Report. National Institutes of Health, National Institutes of Diabetes and Digestive and Kidney Diseases. Bethesda, MD, 1996. United States Renal Data System. USRDS 1997 Annual Data Report. National Institutes of Health, National Institutes of Diabetes and Digestive and Kidney Diseases. Bethesda, MD, 1997. Wolfe RA. The standardized mortality ratio revisited: Improvements, innovations, and limitations. Am J Kidney Dis 1994; 24:29-297. Wolfe RA, Gaylin DS, Port FK, Held PJ, Wood CL. Using USRDS generated mortality tables to compare local ESRD mortality rates to national rates. Kidney Int 1992; 42:991-996. 132