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Nephrologist Care and Mortality in Patients With Chronic Renal Insufficiency
Jerry Avorn, MD;
Rhonda L. Bohn, ScD;
Elliott Levy, MD, MPH;
Raisa Levin, MS;
William F. Owen, Jr, MD;
Wolfgang C. Winkelmayer, MD, ScD, MPH;
Robert J. Glynn, ScD
Arch Intern Med. 2002;162:2002-2006.
ABSTRACT
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Background For patients with chronic renal insufficiency, rates of referral to
nephrologists are highly variable, and little is known about the effect of
such consultation on clinical outcomes. We sought to determine whether early
or frequent access to nephrologist care prior to the initiation of dialysis
was associated with a difference in mortality rates in the first year after
dialysis began.
Methods We identified all patients in the New Jersey Medicaid and Medicare programs
who began maintenance dialysis during a 6-year period and who had been diagnosed
with renal disease more than 12 months prior to dialysis. Use of nephrologist
services was documented during this 1-year period, along with other clinical
and sociodemographic variables. The outcome measure of our analysis was mortality
in the first year after initiation of dialysis.
Results From multivariate analyses, we found that patients who did not see a
nephrologist until 90 days or less before initiation of dialysis had a 37%
higher likelihood of death in the first year of dialysis compared with patients
with earlier referral (95% confidence interval, 1.22-1.52; P<.001). Similarly, those who saw a nephrologist on fewer than 5
occasions in the year prior to dialysis had a 15% higher mortality rate in
the first year of dialysis compared with those who had had 5 or more nephrologist
visits (95% confidence interval, 1.03-1.28; P = .01).
Conclusions For patients with long-standing renal disease, earlier consultation
with a nephrologist and more frequent specialist encounters is associated
with lower mortality in the first year of dialysis. These findings need to
be confirmed in younger and less indigent patients as well.
INTRODUCTION
WITH INCREASING pressures on all aspects of health care expenditures,
and growing concern about the cost-effectiveness of medical interventions,
attention has turned to the role of the specialist in various domains of patient
care. Many payers and health care systems have placed renewed emphasis on
the role of the primary care physician as both coordinator of services and
as "gatekeeper" in rationing access to costly interventions. When done optimally,
this can reduce unnecessary expenditures and improve the coordination of care.
However, excessive application of such pressures can result in denial of access
to more costly services, even when these are clinically appropriate and may
be cost-effective.
Chronic renal disease is one arena in which these issues have been debated
in recent years. End-stage renal disease (ESRD) is the only clinical condition
for which the development of a given diagnosis automatically results in coverage
of health care expenditures by the Medicare program, regardless of the age
of the patient. In 1998, the total cost of care for the numerically small
ESRD program was approximately $12 billion, rendering it the most costly single
Medicare program.1 Since the late 1960s, the
care of ESRD patients has been a lightning rod for societal questions about
health care access, equity, and cost.
While dialysis care of ESRD patients is provided almost uniformly by
nephrologists, the predialysis management of chronic renal insufficiency is
a domain in which issues of specialist vs generalist care loom large. Little
is known about the appropriate place of nephrologist care for patients with
chronic renal insufficiency not requiring renal replacement therapy, a phase
that often lasts for several years. Although extensive data are available
through the Medicare ESRD program once patients receive chronic renal replacement
therapy (ie, maintenance hemodialysis, peritoneal dialysis, or renal transplantation),
it is much more difficult to assemble data during the period prior to their
entry into this program. However, this is precisely the period during which
it is most critical to study the effect of care on the subsequent clinical
course of such patients.
Some have argued that early involvement of a nephrologist in such care
can result in better clinical status at the time of initiation of dialysis,
which in turn could result in an improved clinical outcome once dialysis has
begun. Such preparation can include the timely and proactive development of
vascular access required for hemodialysis, and optimization of hematologic,
endocrine, nutritional, metabolic, and hemodynamic function in the face of
progressive renal failure. In 1997, 55% of patients with chronic renal insufficiency
were first seen only within 12 months prior to initiating dialysis, and 33%
were first seen within 3 months of initiating dialysis.2-3
Several previous studies have demonstrated substantial heterogeneity in the
management of patients with chronic renal insufficiency, perhaps related to
the variability of timing and intensity of the interaction with nephrologists.
The annual mortality rate for ESRD patients is approximately 20% per year,
and half these deaths are attributed to cardiovascular complications.4 This mortality translates into a life expectancy that
is only 16% to 37% that of the age-, sex-, and race-matched general population.2 The highest death risk occurs during the incident
year of renal replacement therapy, and is subsequently lower.1, 5
The effect of delayed referral to a nephrologist on morbidity and mortality
has been examined in a limited manner.6 In
a small study,7 patients receiving care from
a nephrologist had shorter hospitalizations to initiate hemodialysis than
did patients cared for by nonnephrologists, or those who received no medical
care at all. Similarly, Hakim et al8 reported
that hospital stays were longer and more costly for patients with chronic
renal insufficiency referred to a nephrologist relatively late in the course
of their disease. Other studies have examined the association of late nephrologist
referral and mortality in new ESRD patients, but have produced conflicting
results.9-12
These studies used different definitions of late vs early referral, and were
limited to small and highly selected samples.
The present study is the most comprehensive to date to examine this
question in a very large population of patients cared for in typical settings.
It was designed to examine the association between the utilization of nephrologist
services by patients with chronic renal insufficiency during the year before
the initiation of chronic dialysis, and mortality during the first year of
renal replacement therapy.
PATIENTS AND METHODS
We identified all patients who began maintenance dialysis between 1991
and mid-1996, and had been active participants in either the Medicare or Medicaid
programs of the state of New Jersey for at least the prior 12 months. All
personal identifiers were transformed into coded study numbers to protect
confidentiality. Maintenance dialysis was identified by the International Classification of Diseases, Ninth Revision (ICD-9) and Current Procedural Terminology codes for hemodialysis,
peritoneal dialysis, renal transplantation, and ESRD. The first record of
maintenance dialysis during this period was referred to as the index claim.
To ensure eligibility in the Medicare or Medicaid programs, patients were
required to have had at least 1 medical encounter of any kind in the year
prior to their first maintenance dialysis procedure. In addition, we required
that the first diagnosis of renal disease have occurred more than 1 year prior
to the initiation of dialysis, to exclude patients with new-onset renal insufficiency
who may not have had the opportunity for many encounters with a nephrologist
prior to dialysis because of the time course of their condition.
Patients were excluded if they had no second dialysis following the
index procedure but survived more than 1 month, if they had more than 2 months
between 2 consecutive dialysis procedures, or if their health care providers
could not be identified. All patient identifiers were transformed into anonymized
untraceable study numbers in all analyses to protect confidentiality.
For each patient, we then defined age, sex, and race on the date of
initiation of maintenance dialysis. We also roughly characterized socioeconomic
status at this point by defining whether the patient had been enrolled in
Medicaid or the New Jersey Pharmaceutical Assistance to the Aged and Disabled
(PAAD) program, a state-specific program that reimburses drug expenditures
for state residents of modest income who are not indigent enough to qualify
for Medicaid. We then defined the frequency and timing of visits with a nephrologist
in the 12 months prior to initiation of maintenance dialysis. Physician specialty
was identified by Medicare and Medicaid specialty codes as well as by Unique
Physician Identification Numbers assigned to all practicing physicians. For
each physician encounter, provider numbers were searched for the specialty
code for nephrologist.
We also extracted information on all hospitalizations, physician visits,
procedures, and nursing home care received by these patients during this period.
This made it possible to identify all diagnoses assigned to these patients
by all clinicians who cared for them, including specific renal diagnoses as
well as comorbidities such as hypertension, diabetes mellitus, congestive
heart failure, ischemic heart disease, and other relevant conditions (Table 1). Death rates were measured in
the year after maintenance dialysis was begun, using data from Medicare and
Medicaid enrollment files.
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Table 1. Characteristics of Study Population
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Referral patterns to a nephrologist were studied using 2 definitions. Late referral was defined as a patient having a first nephrologist
encounter 90 days or less before the initiation of maintenance dialysis. A
second definition, that of frequency of nephrologist care, was defined as the number of encounters with a nephrologist during
the 12 months prior to initiation of maintenance dialysis. This variable was
dichotomized: 5 or more visits vs less than 5 visits.
We developed a proportional hazards regression model to predict the
likelihood of death in the 12 months following initiation of dialysis. Age,
sex, race, PAAD/Medicaid membership as proxy for socioeconomic status, and
underlying renal diagnosis (categorical) were forced into the model. Then
we added the number of predialysis nephrologist visits and the variable for
late referral, respectively, into 2 separate models. Finally, we tested all
other covariates (categories of comorbidity, Charlson comorbidity score, physician
characteristics) for individual significance or confounding. We also tested
for significance of potential effect modifiers, most importantly the interaction
between age and timing of referral.13
RESULTS
We identified 17 884 patients who underwent maintenance dialysis
at some point during the period 1991 to 1996; of these patients, 12 557
had adequate baseline data for a full year prior to dialysis in Medicaid and/or
Medicare to permit further study. In this population, 5242 patients had their
first renal diagnosis at least 1 year prior to the initiation of dialysis
and were therefore eligible for further study. Most of the patients without
a previous diagnosis of kidney disease who were eliminated in this step can
be assumed to have undergone one-time or short-term renal replacement therapy
as a consequence of acute renal failure. Six hundred twenty-six patients in
this group of 5242 patients had less than 30 days of renal replacement therapy,
indicating that they had acute renal failure. Five hundred ninety-nine patients
had more than 2 months without claims for renal replacement therapy and survived
without additional dialysis care, and 1003 lacked adequate data describing
their health care providers. This left a study population of 3014 patients.
Of these, 1430 (47.4%) died in the first year of dialysis.
As seen in Table 1, the
study population included large numbers of older patients, with 1288 (42.7%)
between the ages of 65 and 74 years and 1063 (35.3%) aged 75 to 84 years.
There were slightly more men than women (56.2% vs 43.8%), and 25.7% were nonwhite.
The most common renal diagnoses specified were hypertensive nephropathy and
diabetic nephropathy. Approximately one third of patients (34.5%) did not
see a nephrologist until 90 days or less before their first renal replacement
therapy. Half of the patients (50.5%) had fewer than 5 nephrologist consultations
in the year prior to renal replacement therapy.
As expected, age was a strong predictor of the likelihood of mortality,
with the risk ratio for death (compared with a referent group aged <45
years) increasing systematically from 2.97 for patients aged 45 to 54 years,
to 11.53 for patients 85 years and older (Table 2). After controlling for clinical diagnoses (see below),
we found no association between sex and mortality. However, blacks were found
to have a lower risk of mortality, as reported in other studies of ESRD,14 with a risk ratio of 0.77 (P<.001).
Individuals of race other than white or black were at even lower risk of death
in their first year on renal replacement therapy (risk ratio, 0.65; P = .002). Being enrolled in either the New Jersey Medicaid
or PAAD programs, which served as a proxy for lower socioeconomic status,
was not significantly predictive of higher mortality (risk ratio, 0.97; P = .57).
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Table 2. Proportional Hazards Regression Model of Risk Factors for
Mortality in the First Year of Maintenance Dialysis*
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After controlling for age, race, socioeconomic status, and the presence
of all renal diagnoses recorded in the year before dialysis (Table 2), we examined the risk of death independently associated
with late referral to a nephrologist as defined above, using proportional
hazards regression analysis. Patients with late referral (first nephrologist
consultation  90 days before initiation of dialysis) had a 37% increase
in risk of death in the first year of dialysis compared with patients whose
first nephrologist encounter occurred more than 90 days before the start of
dialysis (95% confidence interval, 22%-52%; P<.001).
We next replaced this variable in the model with a variable defining
the frequency of nephrologist visits during the 12 months prior to initiation
of dialysis. Here again, after controlling for all other variables studied,
patients who had seen a nephrologist fewer than 5 times in the year prior
to initiation of dialysis had a 15% higher risk of death in the subsequent
year, compared with those who saw a nephrologist more frequently during that
period (P = .01). Adjusting for the Charlson comorbidity
score and for other specific nonrenal clinical conditions (eg, diabetes, ischemic
heart disease) yielded essentially identical results (risk ratiolate
referral, 1.35; P<.001). In using interaction
terms to study whether the effect of late referral differed by age group,
we found that the effect was not significantly changed by the age of the patient.
COMMENT
These findings are based on what is, to our knowledge, the largest study
to date of predialysis patients, and raise important questions about access
to and utilization of nephrologist services in this vulnerable population.
The excess mortality seen in patients with chronic renal insufficiency who
have late or infrequent consultation with nephrologists does not appear to
be an artifact caused by differences in patients' ages, sex, cause of their
renal disease, socioeconomic status, or other comorbid conditions.
The present study may help reconcile the conflicting results among previous,
smaller studies. While Ifudu et al9 (United
States), Innes et al10 (United Kingdom), and
Sesso et al11 (Brazil) had found an increase
in mortality in patients with delayed nephrological care, Roubicek et al12 (France) did not find an increase in 1-year or 5-year
mortality in patients who first saw a nephrologist less than 4 months prior
to onset of dialysis. However, differences in methodology and populations
under study probably confounded these previous results.15
The largest population in which this question was studied previously contained
only 270 subjects,12 compared with the 3014
in the present report. The failure to find a difference in survival between
patients referred to a nephrologist late vs early in previous studies is probably
attributable to selection bias, or problems in generalizability from one population
to another, particularly when cross-national health system issues are considered.
Friedman15 has pointed out that the frail or
elderly patients most vulnerable to delayed referral may be less likely to
receive renal replacement therapy in France, while such patients with high
comorbid health status and age, who may benefit most from timely nephrologist
consultation, are likelier to receive treatment in the United States.
Although extensive outcome data are available through Medicare and its
associated ESRD registries, it is more difficult to assemble data describing
patients prior to their renal replacement therapy. However, this period is
critical to study the effect of care on the subsequent clinical course of
such patients. In evaluating these findings, some limitations of the study's
reliance on Medicare and Medicaid data must be kept in mind. For patients
younger than 65 years, the only source of predialysis information was care
received through the Medicaid program, raising concerns about whether data
from this group of patients can be generalized to younger, nonindigent patients
with these conditions. However, for all patients who began dialysis after
age 66, predialysis enrollment in Medicare was virtually universal, and we
found no difference in the effect of nephrologist referral in this age group
compared with younger patients (P = .21). Second,
because the diagnoses were based in part on data from inpatient and outpatient
encounter claims from the Medicare and Medicaid programs, there is a possibility
of misclassification with regard to the cause of ESRD or other clinical conditions.
Assessment of renal diagnosis was approached differently in the present study
compared with United States Renal Data System (USRDS) data. In the USRDS data
set, renal diagnosis is drawn from the HCFA [Health Care Financing Administration]
2728 form, where providers of renal replacement therapy enter the most likely
renal diagnosis for a given patient. Instead, we screened for all renal diagnoses
assigned in the year prior to onset of maintenance dialysis by all physicians
and hospitals caring for the study subjects. Hence, renal diagnoses are not
mutually exclusive in our study. Nonetheless, even in studies using primary
medical records, the attribution of ESRD to a particular clinical cause is
often difficult and often suspect, because most patients with chronic renal
insufficiency do not undergo diagnostic renal biopsy; it is not unusual for
patients to receive the default diagnosis of "hypertensive nephropathy" or
"diabetic nephropathy" in such primary sources.
We also considered possible confounding by nonrenal clinical conditions,
such as diabetes, hypertension, malignancy, congestive heart failure, or coronary
heart disease. As expected, there was high collinearity between some comorbidities
(eg, diabetes) and their related renal diagnoses (eg, diabetic nephropathy).
When adding comorbid conditions to the model, or when replacing renal comorbidities
with nonrenal comorbid conditions, the observed findings were virtually identical
(risk ratiolate referral, 1.35; P<.001).
It is possible that the sudden onset of rapidly progressive renal failure
might have been associated both with a higher death rate on dialysis as well
as with a lower rate of nephrologist visits in the preceding year. However,
this possibility was addressed by requiring that all patients studied have
a diagnosis of chronic renal failure extending at least a full year prior
to the initiation of dialysis.
Our findings cannot at this point resolve the question of whether the
utilization of nephrologist services may also serve as a marker for other
characteristics that may also be important risk factors for mortality in ESRD.
Socioeconomic status does not appear to play a role, since we did not find
an increased adjusted risk of death in Medicaid or PAAD patients compared
with those who were less indigent. However, use of specialist services may
correlate with other issues of access and quality of care, which in themselves
may play an important role in outcomes. For example, patients who are referred
to a nephrologist may have a primary care physician who is also more conscientious
at managing other aspects of their care, such as hypertension or nutrition.
Or, such patients may themselves be more compliant with recommendations for
their care, or more adept at navigating the health care system.
Alternatively, the nephrologist involvement may make referred patients
more likely to be treated with erythropoietin for anemia, possibly lowering
the risk of death, or to have a permanent vascular access created for maintenance
dialysis, especially a primary fistula. This in turn may reduce infectious
risk during renal replacement therapy and/or improve dialysis doses. Other
testable hypotheses are that patients who see a nephrologist earlier and more
often have better treatment of comorbid conditions associated with progressive
renal failure, such as hypertension, malnutrition, and/or hyperphosphatemia,
or may be better prepared psychologically for dialysis, resulting in better
compliance with dietary and/or fluid regimens. If processes of care for pre-ESRD
patients differ across specialties and these differences can have a beneficial
impact on ESRD mortality, follow-up studies will be necessary to further define
these and other possibilities. This may be of particular importance if manpower
constraints in the coming years limit the number of nephrologists available
to provide such additional care; might there be some particular interventions
that could also be performed by a primary care physician or another consultant
if nephrologist care were in short supply?
If these findings are replicated in other settings, especially in younger
and less indigent cohorts, it will be important to further define the mechanism
through which early and/or more frequent nephrologist input appears to have
a beneficial effect on patient outcomes. If confirmed, such findings could
have important implications for quality improvement programs,16-17
manpower projections,18-19 the
care of particular high-risk populations,20
as well as health policy and resource allocation decisions.21
AUTHOR INFORMATION
Accepted for publication February 6, 2002.
This work was supported by grant R0-1-HS09398 from the Agency for Healthcare
Research and Quality. Additional support was provided by the Health Care Financing
Administration.
Corresponding author and reprints: Jerry Avorn, MD, Division of Pharmacoepidemiology
and Pharmacoeconomics, Brigham and Women's Hospital, 221 Longwood Ave, BLI/341,
Boston, MA 02115.
From the Division of Pharmacoepidemiology and Pharmacoeconomics (Drs
Avorn, Bohn, Winkelmayer, and Glynn and Ms Levin), Division of Nephrology
(Drs Levy and Owen), Department of Medicine, Brigham and Women's Hospital,
Harvard Medical School, Boston, Mass. Dr Levy is now with Bristol-Myers Squibb
Pharmaceutical Research Institute, Princeton, NJ, and Dr Owen is with Duke
Institute of Renal Outcomes Research and Health Policy, Duke University Medical
Center, Durham, NC.
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