Tohoku J. Exp. Med., 2014, 233, 9-15 Epidemiology of Acute Abdominal Pain in Japan

9

Age-Related Differences in Outcomes and Etiologies of Acute
Abdominal Pain Based on a National Administrative Database
Atsuhiko Murata,1 Kohji Okamoto,2 Toshihiko Mayumi,3 Keiji Maramatsu1 andShinya Matsuda1
1

Department of Preventive Medicine and Community Health, School of Medicine, University of Occupational andEnvironmental Health, Kitakyushu, Fukuoka, Japan2
Department of Surgery, Yahata Municipal Hospital, Kitakyushu, Fukuoka, Japan3
Department of Emergency Medicine, University of Occupational, Environmental and Health, Kitakyushu,
Fukuoka, Japan

Acute abdominal pain is one of the most frequent causes of admission to emergency departments.
However, there is a shortage of detail information showing the difference of outcomes or etiology of acuteabdominal pain according to age. We therefore conducted an epidemiological analysis to reveal thedifference between age on outcomes and etiology of acute abdominal pain using an administrative
database associated with the Diagnosis Procedure Combination (DPC) system. We obtained discharge
data relating to 12,209 patients with acute abdominal pain from 931 DPC participation hospitals between
2009 and 2011 in Japan. We compared length of hospital stay (LOS), in-hospital mortality, and etiology ofacute abdominal pain between age categories. Patients were divided into five age groups as follows: < 20
(n = 1,106), 20-39 (n = 3,353), 40-59 (n = 2,925), 60-79 (n = 3,144), and ≥ 80 years (n = 1,681). Longer
LOS and higher in-hospital mortality were observed in patients aged ≥ 80 years (p < 0.001). Regarding
etiologies of acute abdominal pain, intestinal infection or acute appendicitis were more frequent in patients
aged < 20 or 20-39 years, while ileus or cholelithiasis were more frequent in patients aged 60-79 or ≥ 80
years in both male and female patients (p < 0.001). This study demonstrated the significant differences
between age with regard to the patient outcomes and etiology of acute abdominal pain. The current
findings highlight the importance of improving the quality of medical care for patients with acute abdominal
pain.
Keywords: acute abdominal pain; administrative database; age; Diagnosis Procedure Combination; epidemiology
Tohoku J. Exp. Med., 2014 May, 233 (1), 9-15. © 2014 Tohoku University Medical Press
patients visited an emergency department in 2006 for acuteabdominal pain (Pitts et al. 2008). Thus, acute abdominal
pain has been one of the most frequent causes of admission
to emergency departments globally.
However, little information is available on the epidemiology of acute abdominal pain using patient-based data
in Japan. In addition, there have been no studies showing
the difference in outcomes or etiology of acute abdominal
pain according to age based on a national administrative
database. This type of information could contribute to studies on the quality of patient medical care for acute abdominal pain, which could have significant implications forhealthcare policy decision making. In this study, we investigated the difference in outcomes and etiology of acuteabdominal pain according to age. This was achieved using
the national administrative database developed in a
Japanese case-mix system project named the Diagnosis
Procedure Combination (DPC).

Introduction
Acute abdominal pain is defined as severe pain arisingin the abdominal area requiring immediate care (Macaluso
and McNamara 2012). The wide variety in presentation ofsymptoms and the broad spectrum of associated diseases
complicates the isolation of the cause of abdominal pain,
which may vary from life-threatening diseases requiring
emergency surgery to mild self-limiting causes (Laméris etal. 2009). The prevalence of patients with acute abdominal
pain has been increasing over the years (Pitts et al. 2008;
van Randen et al. 2011). Hastings and Powers (2011) conducted a retrospective study in patients with acute abdominal pain at three different time points over a period of 35
years, and reported that there was an increased tendency inthe proportion of patients presenting with acute abdominal
pain as a chief complaint. According to the National Health
Statistics report in the USA, approximately eight million

Received February 6, 2014; revised and accepted March 27, 2014. Published online April 17, 2014; doi: 10.1620/tjem.233.9.
Correspondence: Atsuhiko Murata, M.D., Ph.D., Department of Preventive Medicine and Community Health, School of Medicine,
University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu, Fukuoka 807-8555, Japan.
e-mail: amurata@med.uoeh-u.ac.jp

910A. Murata et al.

Methods
The DPC system was introduced into 82 academic hospitals in2003 (Murata et al. 2010, 2011, 2012). Insurance reimbursements
using the DPC system are widespread in Japan, and the administrative
database of the DPC system has increased the representation of acutecare hospitals over time. As of 2007, data from approximately
450,000 inpatients have been compiled, representing approximately
90% of all acute care inpatient hospitalizations in Japan (Murata et al.
2010, 2011, 2012). The DPC administrative database includes eachpatient’s discharge summary and claim information, including principal diagnosis (disease which triggered admission or main disease ondischarge), comorbidities at the time of admission, and complications
during hospitalization (Kubo et al. 2011). These data are coded using
the International Classification of Diseases and Injuries 10th Revision(ICD-10th) code. This administrative database also contains detailed
medical information, such as all interventional or surgical procedures,
medications, and devices that are indexed in the original Japanese
code. These codes are determined by the Ministry of Health, Labourand Welfare of Japan. The DPC database also includes the quantityand date of all care delivered on a daily basis during hospitalization(Murata et al. 2010, 2011, 2012).
Study setting
We selected 12,209 patients admitted for acute abdominal painin 931 DPC participation hospitals (83 academic and 848 community
hospitals) between 2009 and 2011. These hospitals are situatedthroughout Japan and play leading roles in providing acute care medicine, advancing medical research, and educating students and medical
residents (Murata et al. 2010, 2011, 2012). The principal diagnosis ofacute abdominal pain was recorded using the ICD-10th code. In thepresent analysis, acute abdominal pain was defined as code R100.
For clarification of the difference of outcomes and etiology of acuteabdominal pain according to age, patients were divided into five agegroups as follows: < 20 years (n = 1,106), 20-39 years (n = 3,353),
40-59 years (n = 2,925), 60-79 years (n = 3,144), and ≥ 80 years (n =1,681).
The use of DPC data was permitted by all institutions and hospitals that provided detailed data. The research protocol of the study
was approved by the ethics committee of medical care and researchof the University of Occupational and Environmental Health,
Kitakyushu, Japan.
Study variables
We collected data in the administrative database on the clinicalcharacteristics of patients and hospitals as follows: the etiology ofacute abdominal pain, age, sex, use of ambulance or intensive careunit (ICU), presence of chronic comorbid conditions and surgicaltreatments, the proportion of hospitals with emergency centers, hospital type and size, length of stay (LOS), and in-hospital mortality.
Regarding the etiology of acute abdominal pain, we defined the maindisease on discharge as the etiology of acute abdominal pain in thisstudy. To assess the severity of chronic comorbid conditions, we used
the Charlson Comorbidity Index (CCI), the most widely used index
of comorbidity, which has been validated in various studies. The CCI
was expressed as the score of comorbid conditions and initially evaluated as a continuous variable. The categorical variables of CCI defining four categories for the severity of the comorbid conditions werecreated to simplify the presentation of the results: 0 and 1, mild; 2,

moderate; and 3 or more, severe (Murata et al. 2010, 2011, 2012).
The presence of surgical treatments for patients was determined by
the data of the operation code. Hospital type was classified as academic or community. Hospital size was categorized into three groups
according to the number of hospital beds: small (< 200 beds), medium(200-600 beds), and large (> 600 beds) (Murata et al. 2010, 2011,2012). Hospitals with emergency centers were confirmed by theJapanese Association for Acute Medicine homepage.
Statistical analysis
For tests of statistical significance, we used the Chi-squared test
for categorical data, and one-way factorial analysis of variance forcontinuous variables. In addition, we performed the Scheffe’s or
Tukey’s multiple-comparison test to demonstrate the difference
between each age group. Analyses of outcomes such as LOS and inhospital mortality were performed separately according to the presence of surgical treatments while analyses of etiology of acuteabdominal pain were performed for each sex in this study.
A value of p < 0.05 was considered significant. All statisticalanalysis was performed using the STATA statistical software package
version 11.0 (Stata Corporation, College Station, TX, USA).

Results
12,209 patients were identified for this study: 5,268
male and 6,941 female patients. The mean LOS was 11.1
days while the in-hospital mortality was 2.3% between
2009 and 2011. One hundred and fifty-eight etiologies ofacute abdominal pain were observed in this study.
Characteristics of patients and hospitals are shown in
Table 1. Use of ambulance and ICU, and the proportion ofpatients with severe comorbid conditions significantly
increased according to age categories ( p < 0.001). Surgicaltreatments were significantly more likely to be performedin patients aged 60-79 years or in those aged ≥ 80 years ( p< 0.001). Regarding hospital characteristics, patients aged
< 20 years were more likely to be admitted to hospitals withemergency centers or academic hospitals (29.4% and13.6%; p < 0.001, respectively). A significant variation inmean LOS was observed between age categories in bothpatients with and without surgical treatments ( p < 0.001),
except for comparison between patients aged less than 20
years and those aged 20-39 years by the Scheffe’s multiplecomparison test (5.0 days and 5.6 days: p = 0.755, 8.9 days
and 11.9 days: p = 0.660, respectively). In addition, in-hospital mortality was significantly higher in patients aged 80
years who required surgical treatment ( p < 0.001).
Etiology of acute abdominal pain by sex is shown in
Table 2. Intestinal infection was the most frequent etiologyof acute abdominal pain in both male and female patients(11.5% and 11.0%, respectively). Acute appendicitis was
the second most frequent etiology in male patients whereas
the ileus was the second most frequent in female patients(9.2% and 8.0%, respectively). Digestive diseases such asperitonitis, cholelithiasis, or gastric ulcer were frequent inmale patients while gynecological diseases such as neoplasms or inflammatory and non-inflammatory diseases of
the uterus or ovary were frequent in female patients.

11

Epidemiology of Acute Abdominal Pain in Japan
Table 1. Clinical characteristics and presentations of patients sorted by age categories.
Less than 20 years(n = 1,106)

20-39 years(n = 3,353)

40-59 years(n = 2,925)

60-79 years(n = 3,144)

80 years or more(n = 1,681)

p value

Mean age (year)

13.3*

30.1*

49.0*

69.8*

85.7*

< 0.0011)

Male patients (%)

45.4

29.6*

47.6

55.5*

37.6*

< 0.0012)

Use of ambulance (%)
Use of intensive care unit (%)

19.0*
0.8

31.1
1.1

33.6
1.9

34.8
4.5*

40.9*
6.0*

< 0.0012)< 0.0012)

Comorbid conditions (%)
None (CCI:0)

90.0*

83.2*

67.3*

50.1

48.6

< 0.0012)

Mild (CCI:1)
Moderate (CCI:2)
Severe (CCI:3 or more)
Surgical treatments (%)

7.6
2.0
0.4
18.7

11.1
4.4
1.3
18.4

18.3
8.4
6.0
22.0

22.4
16.1
11.4
28.8

25.6
14.4
11.4
26.1

< 0.0012)

29.4

29.1

23.7

21.0

19.9

< 0.0012)

Academic hospitals (%)

13.6*

9.0*

6.6

6.0

4.4

< 0.0012)

Hospital size (%)
Small sized (less than 200 beds)

9.6

10.6

12.7

14.5

15.3

< 0.0012)

Medium sized (200-600 beds)
Large sized (more than 600 beds)
Patient outcomes
Mean length of hospital stay (days)
Patients without surgical treatments

66.5
23.9

67.0
22.4

68.7
18.6

69.3
16.2

70.2
14.5

5.0

5.6

7.5*

10.6*

13.0*

< 0.0011)

Patients with surgical treatments

8.9

11.9

17.8*

25.5*

31.9*

< 0.0011)

In-hospital mortality (%)
Patients without surgical treatments

0.0

0.04

0.4

2.7*

7.7*

< 0.0012)

Patients with surgical treatments

0.0

0.3

1.5

5.3*

11.6*

< 0.0012)

Patient characteristics

Hospital characteristics
Hospitals with emergency center (%)

P value was derived from analysis of variance (1) and the Chi-square test (2).
*Statistically significant difference against all other age groups by the Scheffe’s or Tukey’s multiple-comparison test ( p < 0.05.
For example, mean age of patients aged less than 20 years (13.3 years) is statistically different from those aged 20-39 years (30.1
years, p < 0.001), 40-59 years (49.0 years, p < 0.001), 60-79 years (69.8 years, p < 0.001) and 80 years or more (85.7 years, p <0.001)).
CCI, Charlson Comorbidity Index.

Intestinal infection or acute appendicitis became frequent in accordance with lower age ( p < 0.001), and the
Tukey’s multiple-comparison test showed the statisticallydifference for less than 20 years, 20-39 years and 40-59
years group. Conversely, ileus or cholelithiasis was more
frequent in patients aged 60-79 years or in those aged 80
years or more ( p < 0.001). Gastrointestinal disease such as
diverticular intestinal disease, gastric ulcer, gastritis, andduodenitis were significantly more frequent in patients aged
40-59 years ( p < 0.001; Table 3).
As with male patients, intestinal infection or acuteappendicitis was more common in female patients aged lessthan 20 years or in those aged 20-39 years, while ileus wasmore common in patients aged 60-79 or ≥ 80 years ( p <0.001). However, gynecological diseases such as uterine orovarian neoplasms or inflammatory and non-inflammatory
diseases of the uterus or ovary were significantly morecommon in patients aged 20-39 years ( p < 0.001), and the
Tukey’s multiple-comparison test showed the statisticallydifference between those aged 20-39 years and all other age
groups. Gastrointestinal disease such as gastritis and duodenitis, diverticular disease of the intestine, or gastric ulcer
were significantly more common in patients aged 40-59
years ( p < 0.001; Table 4).

Discussion
We investigated the difference in outcomes and etiology of acute abdominal pain between age categories using anational administrative database. Our study revealed a significant effect of age on outcome and etiology of acuteabdominal pain in Japanese patients.
In this study, patients aged 80 years or more were significantly associated with a longer LOS and higher in-hospital mortality, particularly after surgical treatments. Ourcurrent results have been consistent with those of several
previous studies (van Geloven et al. 2000; Hustey et al.
2005; Lewis et al. 2005). In a retrospective study focusing
on elderly patients in the early 2000s, van Geloven et al.

12

A. Murata et al.
Table 2. Etiology of acute abdominal pain by sex categories (top 20 diseases).
Male patients (n = 5,268)
Etiology

Female patients (n = 6,941)

Number of case (Rate)

Etiology

Number of case (Rate)

Intestinal infection

606 (11.5%)

Intestinal infection

765 (11.0%)

Acute appendicitis
Ileus
Peritonitis
Cholelithiasis
Diverticular disease of intestine
Gastric ulcer
Calculus of urinary tract
Gastritis and duodenitis
Acute pancreatitis
Constipation
Acute cholecystitis
Duodenal ulcer
Postprocedural disorders of digestive system
Vascular disorders of intestine
Colorectal cancer
Dyspepsia
Perforation of intestine
Acute cholangitis
Hernia483 (9.2%)
481 (9.1%)
335 (6.4%)
328 (6.2%)
213 (4.0%)
208 (4.0%)
157 (3.0%)
146 (2.8%)
134 (2.5%)
121 (2.3%)
112 (2.1%)
112 (2.1%)
110 (2.1%)
103 (2.0%)
81 (1.5%)
68 (1.3%)
59 (1.1%)
56 (1.1%)
48 (0.9%)

Ileus
Neoplasm of uterus or ovary
Acute appendicitis
Inflammatory disease of uterus or ovary
Peritonitis
Non-inflammatory disease of uterus or ovary
Diseases associated with pregnancy
Cholelithiasis
Constipation
Gastritis and duodenitis
Diverticular disease of intestine
Vascular disorders of intestine
Gastric ulcer
Postprocedural disorders of digestive system
Calculus of urinary tract
Endometriosis
Acute cholecystitis
Acute pancreatitis
Colorectal cancer

557 (8.0%)
548 (7.9%)
498 (7.2%)
459 (6.6%)
330 (4.8%)275 (4.0%)
238 (3.4%)
227 (3.3%)
226 (3.3%)
192 (2.8%)
186 (2.7%)
167 (2.4%)
147 (2.1%)
118 (1.7%)
111 (1.6%)
92 (1.3%)
91 (1.3%)
86 (1.2%)
67 (1.0%)

Table 3. Etiology of acute abdominal pain in male patients (top 20 diseases; %).
Less than 20 years 20-39 years(n = 503)(n = 994)
Intestinal infection
Acute appendicitis
Ileus
Peritonitis
Cholelithiasis
Diverticular disease of intestine
Gastric ulcer
Calculus of urinary tract
Gastritis and duodenitis
Acute pancreatitis
Constipation
Acute cholecystitis
Duodenal ulcer
Postprocedural disorders of digestive system
Vascular disorders of intestine
Colorectal cancer
Dyspepsia
Perforation of intestine
Acute cholangitis
Hernia

26.4*
29.6*
7.9
4.5
0.2
0.9
0.9
0.6
0.9
0.6
5.5
0.2
0.4
0.4
0.4
0.0
1.5
0.2
0.0
0.9

18.2*
16.4*
5.9
7.3
2.9
4.4
4.7
4.7
3.7
2.2
1.0
1.1
3.4
0.8
0.4
0.2
2.3
0.1
0.3
0.7

40-59 years(n = 1,394)

60-79 years(n = 1,745)

80 years or more(n = 632)

p value

10.9*
7.0*
6.8
6.7
6.1
6.1
5.7
4.3
4.5
3.6
1.1
2.0
3.3
1.1
1.4
1.4
1.6
0.8
1.0
1.0

5.7
3.6
11.6
5.9
9.0
3.5
3.2
2.5
1.8
2.8
2.1
3.1
1.4
3.5
2.9
2.4
0.6
1.8
1.6
0.9

6.1
1.5
13.1
6.4
8.7
2.8
3.1
0.3
1.2
1.4
4.5
2.5
0.4
3.4
4.1
2.5
0.4
1.9
1.5
0.9

< 0.001< 0.001< 0.001
0.273< 0.001< 0.001< 0.001< 0.001< 0.001
0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001
0.001< 0.001
0.001
0.957

All p values were derived from the Chi-square test.
*Statistically significant difference against all other age groups by the Tukey’s multiple-comparison test ( p < 0.05).

13

Epidemiology of Acute Abdominal Pain in Japan
Table 4. Etiology of acute abdominal pain in female patients (top 20 diseases; %).
Less than 20 years(n = 603)

20-39 years(n = 2,359)

40-59 years(n = 1,531)

Intestinal infection

25.0*

13.7

10.2

Ileus
Neoplasm of uterus or ovary
Acute appendicitis
Inflammatory disease of uterus or ovary
Peritonitis
Non-inflammatory disease of uterus or ovary
Diseases associated with pregnancy
Cholelithiasis
Constipation
Gastritis and duodenitis
Diverticular disease of intestine
Vascular disorders of intestine
Gastric ulcer
Postprocedural disorders of digestive system
Calculus of urinary tract
Endometriosis
Acute cholecystitis
Acute pancreatitis
Colorectal cancer

4.9
3.6
24.8*
3.0
3.4
2.9*
1.5
0.1
5.2
1.3
0.5
0.3
1.2
0.3
0.5
0.0
0.2
0.4
0.0

4.6
7.8
11.0*
8.4*
5.2
5.9*
6.3*
1.8
1.7
3.2
3.2
0.5
2.3
0.6
2.6
1.7
0.6
1.2
0.2

8.5
5.9
6.2
4.4
5.7
1.3*
0.2
5.0
1.7
3.5
4.9
1.8
4.2
1.6
3.3
1.0
1.4
2.4
1.1

60-79 years(n = 1,399)

80 years or more(n = 1,049)

p value

6.8

7.1< 0.001

11.3
1.6
3.9
0.3
5.8
0.1
0.0
7.3
2.8
2.1
3.1
3.7
2.8
3.3
2.0
0.0
2.9
2.3
2.3

13.0
1.1
1.9
0.1
5.8
0.1
0.0
6.7
5.3
2.5
2.4
4.5
2.9
3.0
0.7
0.0
2.8
1.4
1.9

< 0.001< 0.001< 0.001< 0.0010.028< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001

All p values were derived from the Chi-square test.
*Statistically significant difference against all other age groups by the Tukey’s multiple-comparison test ( p < 0.05).

(2000) reported that the mortality of admitted patients aged
over 80 years with acute abdominal complaints was 17%
while that of patients with urgent surgery reached 34%.
Some previous studies also reported that elderly patients
had a greater risk of mortality or morbidity compared withyounger patients (Hustey et al. 2005; Lewis et al. 2005). In
addition, severe comorbid conditions were significantly
observed in patients aged 80 years or more. Some previous
studies suggest that comorbid conditions can influence theprognosis or outcomes of patients with acute surgical treatments (Oomen et al. 2006; Bo et al. 2007). Despite recent
advances in the management of acute abdominal pain
including surgical or intensive care treatments, these results
indicate that the mortality of elderly patients with acuteabdominal pain has remained high over the past decade.
Therefore, our results still support the difficulty of managing elderly patients with acute abdominal pain.
However, there was a slight difference with regards toetiology of acute abdominal pain between our study andprevious studies. For example, calculus of urinary tract wasless frequently observed in elderly patients in this study
whereas some studies reported that kidney or urinary tract
diseases were presented in many elderly patients as etiologies of acute abdominal pain in the United States (Hustey etal. 2005; Lewis et al. 2005). We assumed that this discrepancy may be related to the racial or regional differences.
Therefore, further investigations should be required toreveal the etiology of acute abdominal pain of elderly
patients in various countries.
This study also provided some epidemiological information on acute abdominal pain in other age categories.
For example, intestinal infection and acute appendicitis
were more common in younger male and female patientssuch as those aged < 20 or 20-39 years, while gynecological diseases such as neoplasms or inflammatory and noninflammatory diseases of the uterus or ovaries were significantly more common in patients aged 20-39 years. To ourknowledge, there have been no reports on the etiology ofacute abdominal pain by age or sex in a study sample,
although some studies have focused on each etiology ofacute abdominal pain in pediatrics, elderly patients, or
female patients (Leung and Sigalet 2003; Cartwright andKnudson 2008; Kruszka and Kruszka 2010). In addition,
the proportion of younger patients treated in hospitals withemergency center or academic hospitals was significantly
higher in this study, and the in-hospital mortality of thesepatients was very low. Furthermore, there was no significant difference with regard to LOS between patients aged
less than 20 years and those aged 20-39 years. These
results suggest that the centralization of younger patientswith acute abdominal pain to these specific hospitals wasachieved favorably compared with elderly patients. Thus,
this study shows some aspects such as the difference in etiology or treatment situation of acute abdominal pain in14

A. Murata et al.

Japan.
The clinical data used represent a major strength of thecurrent study. Although some studies regarding the outcome and etiology of acute abdominal pain have been published, these reports come from some single-center studies(van Geloven et al. 2000; Gajic et al. 2002; Gardner et al.
2010). One of the benefits of the national database is that it
enables evaluation of a large number of hospitals, and ourinvestigation involved a nationally representative sample ofpatients with acute abdominal pain in a community setting(Murata et al. 2011, 2012). Therefore, using a national
administrative database reveals the present circumstancesof patients with acute abdominal pain for the nation as awhole. In addition, detailed medical data such as patientsor hospital characteristics have been recorded in an unbiased manner (Murata et al. 2010, 2011, 2012). Therefore,
this administrative database enables interested parties toevaluate the outcomes or etiology of acute abdominal painwith individual detailed medical data.
Some potential limitations of this study also warrant
mention. First, the data were obtained from DPC participating hospitals. Therefore, data in non-DPC participating
hospitals should be analyzed to confirm the influence of the
DPC system in the future. Second, we could not investigate
the severity of diseases as etiology of acute abdominal painin this study. It is plausible that the severity of diseases significantly influences in-hospital mortality or LOS. Third,
we defined the main disease on discharge as the etiology ofacute abdominal pain using ICD-10th code and peritonitis
was appeared as main disease on discharge in many cases.
However, peritonitis is not primary etiology of acuteabdominal pain because this condition emerges from various diseases such as gastrointestinal perforation or abdominal trauma (Samuel et al. 2011). Third, our data also do notinclude the detailed clinical information such as computed
tomography before admission to hospitals or the rate of
emergency operation in this study. Fourth, because we only
had the discharge data of patients with acute abdominal
pain in this study, we could not assume the number ofpatients discharged without hospitalization. Therefore, further clinical studies evaluating the outcomes or etiology ofacute abdominal pain may be required, taking into accountdetailed clinical data or data of patients who were not hospitalized in the future.
Despite these limitations, the current study has implications for healthcare policy decision making. It may beinsufficient to only specify the rate of surgical cases for
acute abdominal pain. We only obtained the data forpatients as determined by the ICD-10th code (R100),
whereas many patients presenting with acute abdominal
pain may be included in each diagnosis as the principal
diagnosis (e.g. acute appendicitis or ileus) on our administrative database. However, our study may show an important difference in the rate of surgical cases or outcomes
between age categories. Although this study is not someaningful for comprehending the real rate of surgicalcases for acute abdominal pain, it does reveal the differencein circumstances between age categories. Our study may
therefore highlight the importance of improving the qualityof medical care for patients with acute abdominal pain. The
current findings provide good evidence on the present circumstances of patients with acute abdominal pain, and may
be useful in assisting future epidemiological investigationsin Japan. In addition, increasing life expectancy and an
aging population will inevitably lead to a growing numberof elderly patients with abdominal pain in Japan and otherdeveloped countries (Murata et al. 2013). Therefore, consecutive monitoring of outcomes in elderly patients should
be conducted in the future. The monitoring of LOS and inhospital mortality via an administrative database in elderly
patients may be a promising policy initiative, allowing theimprovement of the quality of medical care for elderly
patients. If an improvement in quality of care is achievedin elderly patients, it could be useful for many other countries that have also been facing problems in the quality of
medical care for this population. Further studies of successive monitoring of LOS and in-hospital mortality of elderly
patients should be conducted. In addition, the differencesin etiology of acute abdominal pain should be investigatedin the near future.
In conclusion, this study demonstrated significant differences between age categories in outcomes and etiologyof acute abdominal pain using a national administrative
database. We hope that this study will provide useful information and assist future epidemiological investigations inJapan.

Acknowledgements
This study was funded by Grants-in-Aid for Research on
Policy Planning and Evaluation from the Ministry of Health,
Labor and Welfare, Japan.

Conflict of Interest
The authors declare no conflict of interest.

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