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Abdominal Cross-sectional Imaging for Inpatients With Abnormal Liver Function Test Results
Yield and Usefulness
Jeffrey M. Rothschild, MD, MPH;
Ramin Khorasani, MDCM, FRCPC;
Stuart G. Silverman, MD;
Richard W. Hanson;
Julie M. Fiskio;
David W. Bates, MD, MSc
Arch Intern Med. 2001;161:583-588.
ABSTRACT
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Background Abdominal cross-sectional imaging is often performed to evaluate abnormal
liver function test (LFT) results in hospitalized patients. However, few data
are available regarding the yield and usefulness of imaging inpatients for
the indication of abnormal LFT results, the process of requesting abdominal
imaging studies, or the response to their findings.
Methods We retrospectively reviewed abdominal imaging scans that were obtained
during a 27-month period. We matched the imaging studies done with the indication
of abnormal LFT results; all scans were requested using computerized physician
order entry. Reports were coded for interpretation and associated process
step results. To determine the usefulness of the imaging studies, a random
sample of patient charts with positively coded imaging studies were reviewed.
Imaging examinations were considered useful if they provided new diagnostic
information and/or changed subsequent patient care.
Results Of 6494 abdominal imaging studies, 856 were performed for the indication
of abnormal LFT results and matched to both image reports and laboratory results.
Report coding judged 37% of interpretations as clinically significant, including
27% with "positive" (abnormal results and explain the abnormal LFT results)
examinations. Among the positive examinations, the most common diagnoses were
biliary obstruction (25%), cholecystitis (21%), malignancy (20%), and cirrhosis
(14%). Positively coded reports provided new clinical information in 63% of
these studies and changed patient care in 42% of cases. Process measures assessed
provision of additional information to and from radiologists (69% and 8%,
respectively) and the frequency with which the findings of current abdominal
imaging studies were compared with those of prior studies (59%).
Conclusion Abdominal cross-sectional imaging studies performed on inpatients with
abnormal LFT results had a high diagnostic yield and frequently changed patient
care.
INTRODUCTION
LABORATORY AND radiologic tests have 3 major roles in patient care:
screening, diagnosis, and management1; for
abdominal imaging, diagnosis is most important. Noninvasive diagnostic imaging
is frequently used in the evaluation and management of hospitalized patients
with abdominal disease, especially in the hepatobiliary tract.2
While imaging is often very useful, patients with liver disease can be accurately
diagnosed with only a history, physical examination, and biochemical liver
tests in an estimated 80% of cases.3 The primary
modalities currently used for diagnostic imaging of the liver and biliary
tract are ultrasonography (US), computed tomography (CT), and, to a lesser
extent, magnetic resonance imaging (MRI).4
While radionuclide studies, such as hepatobiliary scintography, are additional
useful noninvasive modalities, they are less frequently requested for the
initial investigation of abnormal laboratory test results. Recent improvements
in noninvasive technologies have markedly changed the roles of interventional
techniques (angiography and cholangiography), and they are now used mostly
in therapeutic or secondary diagnostic roles.2
Cost has also become an important consideration in deciding how to best use
these technologies.5
A common indication for inpatient abdominal imaging is to assist in
the evaluation of abnormal liver function test (LFT) results.3
The liver function tests commonly include (individually or more commonly,
in combination) the measurement of aspartate aminotransferase, alanine aminotransferase,
total and direct bilirubin, and alkaline phosphatase levels. While the term liver function tests is a misnomer because abnormal values
for most of these tests actually reflect hepatocellular damage or dysfunction,
not synthetic or metabolic function,6 it is
widely used in the clinical vernacular.
While imaging is frequently performed in the inpatient setting to address
this issue, few data are available regarding the yield in this population.
Most studies have only investigated outpatient populations when evaluating
the role of imaging modalities during the workup of abnormal LFT results.1 While algorithms for choosing radiologic tests in
the pursuit of a specific pathologic entity (eg, hepatic metastases) or a
certain clinical presentation (eg, right upper quadrant tenderness with a
palpable mass) have been developed,6 less information
is available regarding the evaluation of inpatients with abnormal LFT results
as the primary indication for imaging requests.
Also, it has often been difficult to obtain detailed and accurate information
about the indications selected by physicians who are ordering radiographs.
However, at our institution, all radiographs are ordered online by physicians
using a computerized physician order entry, resulting in nearly complete ascertainment
of indications associated with examination orders.7
We used data from this computerized system to perform a study in hospitalized
patients to assess the yield of abdominal imaging ordered for the indication
of abnormal LFT results. Additional goals included assessing the clinical
usefulness of abdominal imaging for abnormal LFT results, categorizing the
radiologists' diagnoses, and assessing several process steps associated with
both requesting and interpreting abdominal imaging studies.
PATIENTS AND METHODS
STUDY SITE
The study was conducted at Brigham and Women's Hospital, Boston, Mass,
a 700-bed tertiary care teaching hospital. All inpatient diagnostic tests,
including radiologic examinations, are ordered online using a computerized
physician order entry.8 Clinical indications
must accompany radiology requests and are chosen from preselected menus.7 Additional relevant information for the radiologist
can be provided with the request as free text. Commercially available imaging
equipment was used in the study (Somatom Plus 4 CT Scanner; Siemens Medical
Systems, Iselin, NJ, and Acuson XP 128 Ultrasound Machine; Acuson Corp, Mountain
View, Calif).
PATIENT POPULATION AND DATA
Using the hospital information system (Brigham Integrated Computer Systems,
or BICS) database, we retrospectively identified all inpatients for whom abdominal
imaging was requested and performed for the evaluation of abnormal LFT results
during a 27-month period (December 1995–March 1998). All corresponding
radiology reports were retrieved and matched to the electronic requisition.
Imaging examinations completed prior to or after hospitalization were excluded.
OUTCOMES
The main outcome was the diagnostic yield of imaging studies performed
because of abnormal LFT results. Secondary outcomes applied only to examinations
with positive findings (defined below), and included the usefulness of the
imaging findings and process measures associated with imaging requests and
interpretations. Radiographic examinations were considered useful if they
provided the clinician with new information and/or were determined to influence
subsequent diagnostic or therapeutic decisions in patient care.
Radiology reports were reviewed and coded using a fixed coding scheme
(Table 1) by an internist (J.M.R.).
To assess reliability, a random sample of 17% of reports (n = 145) were additionally
coded by an abdominal radiologist (S.G.S.). Diagnostic results were considered
significant if they were abnormal and explained the abnormal LFT results (positive
group) or were abnormal and had significant findings, even if unrelated to
the indication of abnormal LFT results. Clinically insignificant results included
normal or equivocal findings and abnormal findings that were judged to be
insignificant.
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Table 1. Coding Scheme for Diagnostic Imaging Studies
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For those examinations with a positive result, chart reviews were conducted
on a random sample of 108 patient charts (47%) to address the clinical impact
of performing imaging studies because of abnormal LFT results. Abstracting
from the pretest progress notes, the investigators judged that the imaging
findings provided new information if the results were not previously known
(though may have been suspected in the differential diagnosis).
We also wanted to determine if these imaging studies resulted in changes
in subsequent patient care, such as requiring additional confirmatory tests
or assisting in therapeutic decision making (eg, changing code status in response
to finding diffuse metastatic disease or postponing surgical intervention
for improving fluid collections). Other examples of patient care influenced
by imaging results included changes in medical therapy, surgical evaluation
(with or without an operative intervention), or a subsequent procedure, such
as endoscopic retrograde cholangiopancreatography or diagnostic biopsy. The
impact of imaging studies on patient outcomes was not assessed.
Process measures of interest included how often abdominal imaging requests
for evaluating abnormal LFT results included additional clinical information;
how often radiologists provided specific recommendations (in addition to their
interpretations); and how often radiologists included comparisons to prior
studies. The investigators reviewed prior abdominal imaging reports for patients
with positive findings. For determining the frequency of comparison reporting,
the current report was noted for the presence of reference to prior abdominal
CT or US. Prior studies were recorded for examination type (CT or US), for
prior radiographic findings, and if they were conducted during the same hospitalization.
ANALYSIS
Radiographs were categorized as clinically significant or not clinically
significant as described previously. Reliability for coding of imaging reports
was assessed using the  statistic and the percentage of agreement between
reviewers. Diagnostic yield among different imaging modalities was compared
using the  2 statistic. Differences in diagnostic categories
for positive examinations by imaging modality were evaluated using a t test. Information given to radiologists and their recommendations
were also compared using a t test.
RESULTS
During the 27-month study period, there were 89 450 adult admissions
on the medical and surgical services. A total of 6494 abdominal imaging studies
were performed on 3995 inpatients: 4404 CT scans, 1769 US scans, and 321 MRI
scans. Of these studies, 1089 (17%) were performed to evaluate abnormal LFT
results: 429 CT scans, 627 US scans, and 33 MRI scans (Table 2). Imaging requests not matching a radiology report were
excluded (233 requests: 87 US scans, 113 CT scans, and 33 MRI scans), resulting
in a final study group of 856 imaging studies (13%): 316 CT scans, 540 US
scans, and 0 MRI scans.
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Table 2. Abdominal Imaging Studies Ordered for Inpatients*
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DIAGNOSTIC YIELD
The coded results (n = 856) were broadly divided into 2 groups: clinically
significant (37%, n = 313) and clinically not significant (63%, n = 543; Table 3). Clinically significant findings
were much more common among CT scans (180/316, 57%) than among US scans (133/540,
25%; P = .001). The former included findings that
explained the abnormal LFT results (positive findings, 27% [n = 229]), eg,
biliary obstruction, as well as findings that, while unrelated to the abnormal
LFT results, were considered significant and categorized as "abnormal, likely
significant." The abnormal, likely significant studies (10%, n = 84), though
not read as positive, were considered important enough for inclusion in the
clinically significant category. To be included in this category, an explanation
of the abnormal LFT results was not met and many times was clearly unrelated,
eg, finding a new renal mass suggestive of malignancy. The clinically not
significant group was divided into "abnormal, likely not significant" (27%,
n = 231), such as an hepatic cyst; "abnormal, unknown significance" (19%,
n = 161), such as a retroperitoneal fluid collection; "equivocal" (7%, n =
64), such as possible acalculous cholecystis; and "normal" (10%, n = 87).
A second physician validated the reliability of report coding. The level of
agreement between the 2 investigators for the sample was 87% ( = 0.75)
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Table 3. Abdominal Imaging Coded Results*
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Examinations with positive findings were also classified by diagnostic
categories (Table 4). Among both
CT and US studies, the most common diagnostic categories were biliary obstruction/dilatation
(25%); acute or chronic cholecystitis, without obstruction (21%); and mass(es)
consistent with suspected malignancy, either primary or metastatic disease
(20%). A greater proportion of malignancies were found on CT scans (CT, 29%;
US, 10%; P = .001). Positive findngs in the "other"
category included suspicious hepatic fluid collections, such as hematomas
or abscesses. As expected, the US examinations were proportionally more likely
to be associated with abnormalities related to the biliary tract, such as
obstruction (US, 31%; CT, 19%; P = .06) or cholecystitis
(US, 29%; CT, 12%; P = .005).
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Table 4. Diagnostic Categories for Abdominal Imaging Examinations With
Positive Findings*
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Among the 84 examination findings judged as abnormal, likely clinically
significant, CT scans were more often represented (68/316, 22%) than US scans
(16/540, 3%). The most common diagnoses were bowel disease, such as colitis,
obstruction, ischemia (19/84, 23%); pancreatic disease, such as inflammatory
or infectious processes without biliary tract involvement (16/84, 19%); retroperitoneal
adenopathy consistent with metastatic disease (10/84, 12%); nonhepatic solid
organ masses with suspected malignancy (10/84, 12%); massive ascites (5/84,
6%), massive splenomegaly, without mention of portal hypertension or cirrhotic
changes (4/84, 5%) and extrahepatic hematomas (4/84, 5%).
USEFULNESS
A sample of 108 medical charts were randomly selected from the positively
coded group for review (Table 5).
This sample represented 45% of the "positive" (abnormal results and explain
the abnormal LFT results) CT scans (50/112) and 50% of the positive US scans
(58/117). Imaging studies with positive findings provided new clinical information
in 63% of cases (CT, 70%; US, 57%). The new information was sometimes under
consideration and in the documented differential diagnosis, and sometimes
represented an unsuspected finding. The diagnostic categories for imaging
examinations that provided new information included common bile duct obstruction
(22/68, 32%), mass or metastatic disease (12/68, 18%), fatty changes (11/68,
16%), associated pancreatic disease (8/68, 12%), and cirrhosis (4/68, 6%).
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Table 5. Clinical Impact of Abdominal Imaging Results*
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Positive imaging interpretations were associated with documented changes
in patient care in 42% of studies (CT, 50%; US, 34%; Table 5). Categories of changes in patient care included medical
therapy (16/45, 36%);endoscopic retrograde cholangiopancreatography, with
or without a stent procedure (12/45, 27%); surgical evaluation, with or without
surgical intervention (10/45, 22%); diagnostic biopsies (6/45, 13%); and drainage
procedures (1/45, 2%).
PROCESS EVALUATION
Several process steps associated with the request and interpretation
of abdominal imaging were examined (Table
6). Almost all (99%) radiology requisitions for abdominal imaging
included additional patient history and/or signs and symptoms selected from
the order entry menu choices. Additional clinical information was provided
as free text in 69% of the requisitions. Free text examples include surgical
history, hospital course before the imaging orders, patterns of abnormal LFT
results, and results from previous or off-site imaging studies.
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Table 6. Process Evaluation: Information Given to the Radiologist and
Recommendations of the Radiologist
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Further imaging or nonimaging recommendations in the radiology report
were uncommon. Additional recommendations, such as may have taken place via
phone calls or electronic mail sent to the attending physicians or in discussions
with house staff during radiology rounds, were not addressed unless documented
in the imaging report. The recommendations included further imaging in 61
cases (7%) and nonimaging recommendations in 7 cases (1%). The most common
imaging recommendations were for MRI or CT scans following a completed US
study. Nonimaging recommendations were still closely associated with additional
imaging investigations, such as suggesting gastroenterology evaluations for
endoscopic retrograde cholangiopancreatography.
Prior abdominal imaging studies (either the same and/or different modality)
were present in the BICS database for patients who underwent 261 of the current
imaging studies (30%). Radiologists made comparisons to prior abdominal imaging
studies for 153 of those examinations (59%). Current studies compared with
prior imaging included 124 studies in which a change was noted (30 were improved
and 94 were worse) and 29 studies in which there was no change. Findings that
were worse included both progression of previously identified pathologic abnormalities
or a new significant process. In 41% of those studies in which there were
prior abdominal imaging examinations (108/261) (equivalent to 13% of the entire
study group [108/856]), comparisons were not addressed in the current image
examination interpretation. Lack of comparison reporting was much more frequent
for US (106/108, 98%) than for CT (2/108, 2%). Previous studies omitted from
report comparison with current studies included prior CT scans (alone) in
49 cases, prior US scans (alone) in 33 cases, and both imaging modalities
previously performed in 26 cases.
COMMENT
Abdominal imaging, when performed in hospitalized patients because of
abnormal LFT results, yielded clinically significant results in a surprisingly
high proportion of cases. While both types of imaging have their indications,
CT scans were more than twice as likely as US scans to be associated with
clinically significant results. More than two thirds of positive examinations
provided new information explaining the abnormal LFT results. The results
of positive examinations contributed to changes in patient care in 42% of
cases.
The interpretation of abnormal LFT results in the hospital setting,
especially in complex or critically ill patients, can be challenging. The
variable temporal relationship of individual laboratory result abnormalities
to identifiable clinical events may lead to diagnostic obstacles. Liver function
test results are more likely to reflect liver dysfunction occurring days to
weeks before the date of laboratory test sampling rather than that same day.9 Additionally, mild abnormalities have been demonstrated
to be frequent in healthy outpatients.10, 11, 12
Abnormal LFT results may also transiently occur in hospitalized patients without
liver disease, occasionally without explanation.13
The few studies that have been performed to assess the yield of abdominal
imaging studies for the commonly used indication of abnormal LFT results have
been done in outpatients. In a small prospective study of 83 patients with
persistent (>6 months) elevation of aminotransferase levels, 65% of US studies
yielded a pathologic explanation.11 In jaundiced
patients, the yield of hepatic imaging ranges from 52% to 69% to 94% to 97%
of patients with a low and high pretest clinical suspicion, respectively.5 Compared with outpatients, an inpatient population
would be expected to be relatively sicker, yet imaging could result in a lower
yield, especially since many abnormal LFT results could occur as a result
of hypotension, infection, or medications. In all these situations, the abnormal
LFT results would be expected to resolve as the underlying condition improves.
However, diagnostic yield was high.
The abnormal, likely significant category included diseases of the bowel
and pancreas, suspicious extrahepatic masses or fluid collections, massive
splenomegaly, and retroperitoneal adenopathy. While such "unrelated" structural
abnormalities cannot radiologically explain the abnormal LFT results, they
are often associated with medical conditions resulting in hepatic pathophysiologic
dysfunction. For example, abnormal LFT results may result from systemic insults
remote from the hepatobiliary system, such as in multisystem organ dysfunction
that is associated with sepsis or shock.14
Recent reviews of hepatobiliary tract imaging have suggested that while
US remains the modality of choice for gall bladder disease, CT is emerging
as the preferred test for the remaining disorders.2
The other predominant noninvasive imaging technique, MRI, may be more informative
in cases involving suspected hemangiomas, preexisting fatty infiltration with
newly suspected hepatic lesions, and cholangiography in which therapeutic
interventions are not expected.2 In our study,
US examinations were more likely to result in additional imaging studies (either
a second US scan or a different modality, usually CT). Except in cases in
which there is a high degree of suspicion of biliary tract or gall bladder
disease, CT may be the more cost-effective initial imaging study in hospitalized
patients with abnormal LFT results.
Chart reviews of patients with positive imaging results revealed that
imaging in almost two thirds of cases provided new clinical information. Because
imaging modalities were chosen by clinicians, and not randomized, differences
in findings between CT and US cannot be assigned to the sensitivities of imaging
tests for detecting various disease entities. For example, malignant lesions
were more often found on CT scans , while biliary tract disease was more often
found on US scans. Also, other clinical reasons may influence choice of modality,
such as the practicality of US for critically ill patients at risk for transport
to the radiology department or for pregnant patients because of the greater
fetal risks from the radiation exposure of CT. Therefore, no conclusions can
be made from our study with respect to diagnostic categories and the appropriateness
of imaging modalities.
Patient care was determined to have changed in response to imaging results
in 42% of reviewed charts with positive findings. Care included medical (36%)
and interventional or surgical (64%) therapies. The medical responses included
the addition, withdrawal, or modification of specific treatments. The nonmedical
responses were predominantly for additional studies in the form of endoscopic
retrograde cholangiopancreatography, surgical evaluation (with or without
surgery), and diagnostic biopsies.
Determining the clinical impact of diagnostic imaging can be more difficult
than for other types of technology assessment, especially therapeutic interventions.
Imaging efficacy is considered an intermediate outcome.15
"Disaggregating" such diagnostic tests from treatment is difficult to impossible.16 Imaging influences management decisions, and those
decisions may or may not improve patient outcomes. It may be reasonable, therefore,
to consider management decisions as appropriate outcome measures for imaging
studies.16 Nevertheless, modern imaging has
been demonstrated to have an important impact on diagnostic decisions.17
Several components of the process of ordering and interpreting imaging
studies in response to a specific clinical inquiry were addressed in this
study, including documented information shared between clinicians and radiologists.
Pertinent patient history (often including signs and/or symptoms) accompanied
nearly all imaging requests. Study indications (in this sample, abnormal LFT
results) accompanied all imaging requests. This success in providing radiologists
with clinical information is attributable to the entry requirement built into
the order screens. Clinicians must provide this information for imaging requests
to be processed. Order entry screens facilitate this process by providing
menus with preselected common indications. Also, entries can be manually entered
for other indications or relevant clinical data.
In two thirds of imaging requests, additional information for the radiologist
was provided as free text. Despite intuitive expectations as to their helpfulness,
it is uncertain whether more robust clinical information accompanying imaging
requests actually improves the diagnostic accuracy of imaging interpretations.
In addition to interpretation and differential diagnoses, radiologists
occasionally provided management suggestions. In our study, radiologists made
further recommendations in fewer than 10% of cases, and most often were suggestions
to obtain additional imaging, usually with a different modality.
Comparisons to prior imaging studies were performed by the radiologist
in fewer than two thirds of cases. In the remaining cases, although a prior
abdominal imaging study had been performed, a comparison was not made. The
low proportion of reported comparisons may be attributable to a variety of
factors, including the inability to locate the prior studies in a timely fashion.
The implementation of an electronic environment for delivery and interpretation
of imaging studies and their reports (Picture Archiving and Communications
Systems, or PACS) should decrease the number of cases in which a comparison
is not made. Also, enhanced bidirectional communication between clinician
and radiologist may be expected to be facilitated by computerization (eg,
longitudinal electronic medical records).
Our study has several limitations. It took place in a single tertiary
care institution. Because of this and the relatively large number of transplantation
and oncology cases at our institution, our findings may not be generalizable
to all hospitals. The contribution of imaging results to providing useful
new information was analyzed by chart review only for studies with positive
findings. Normal study results (or more commonly in our series, abnormal but
not significant or of unknown significance) may still provide valuable information
in the evaluation of abnormal LFT results. For instance, excluding certain
disease processes can avoid unnecessary exploratory procedures that were more
common in the pre-CT era. Also, the completeness (and possibly the correctness)
of chart documentation was inconsistent, and image reports were not available
for about one fifth of the studies. Furthermore, we did not evaluate the utilization
rates of abdominal imaging for all inpatients with abnormal LFT results. Finally,
our definition of usefulness is based on implicit chart reviews, not on explicit
criteria, and is subject to reviewer bias.
In summary, abnormal LFT results in hospitalized patients were frequent
indications for ordering abdominal imaging studies. Imaging revealed significantly
abnormal findings in about two fifths of studies. Positive imaging results
frequently changed patient care. Further studies are needed to address the
appropriateness and efficacy of abdominal imaging in inpatients with hepatobiliary
disease.
AUTHOR INFORMATION
Accepted for publication August 24, 2000.
From the Division of General Medicine (Drs Rothschild and Bates) and
the Department of Radiology (Drs Khorasani and Silverman and Mr Hanson), Brigham
and Women's Hospital, the Departments of Medicine (Drs Rothschild and Bates)
and Radiology (Drs Khorasani and Silverman), Harvard Medical School, and Clinical
Information Systems, Partners Healthcare System (Ms Fiskio), Boston Mass.
Corresponding author: Jeffrey M. Rothschild, MD, MPH, Division of
General Medicine, Brigham and Women's Hospital, 75 Francis St, Boston, MA
02115.
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