This document describes the development and validation of a new clinical scoring system called the Appendicitis Inflammatory Response Score (AIRS) to aid in the diagnosis of acute appendicitis. The AIRS was constructed using data from 545 patients prospectively admitted for suspected appendicitis. Eight clinical and laboratory variables were identified via logistic regression as having independent diagnostic value and were used to create the scoring system. When validated on 229 additional patients, the AIRS demonstrated superior diagnostic accuracy compared to the existing Alvarado score, with an area under the ROC curve of 0.97 for advanced appendicitis versus 0.92 for the Alvarado score. The AIRS is able to correctly classify the majority of

1. The Appendicitis Inflammatory Response Score: A Tool for the
Diagnosis of Acute Appendicitis that Outperforms the Alvarado
Score
Manne Andersson Æ Roland E. Andersson
Published online: 14 June 2008
Ó Socie´te´ Internationale de Chirurgie 2008
Abstract
Background The clinical diagnosis of appendicitis is a
subjective synthesis of information from variables with ill-
defined diagnostic value. This process could be improved
by using a scoring system that includes objective variables
that reflect the inflammatory response. This study describes
the construction and evaluation of a new clinical appen-
dicitis score.
Methods Data were collected prospectively from 545
patients admitted for suspected appendicitis at four hospi-
tals. The score was constructed from eight variables with
independent diagnostic value (right-lower-quadrant pain,
rebound tenderness, muscular defense, WBC count, pro-
portion neutrophils, CRP, body temperature, and vomiting)
in 316 randomly selected patients and evaluated on the
remaining 229 patients. Ordered logistic regression was
used to obtain a high discriminating power with focus on
advanced appendicitis. Diagnostic performance was com-
pared with the Alvarado score.
Results The ROC area of the new score was 0.97 for
advanced appendicitis and 0.93 for all appendicitis com-
pared with 0.92 (p = 0.0027) and 0.88 (p = 0.0007),
respectively, for the Alvarado score. Sixty-three percent of
the patients were classified into the low- or high-proba-
bility group with an accuracy of 97.2%, leaving 37% for
further investigation. Seventy-three percent of the nonap-
pendicitis patients, 67% of the advanced appendicitis, and
37% of all appendicitis patients were correctly classified
into the low- and high-probability zone, respectively.
Conclusion This simple clinical score can correctly
classify the majority of patients with suspected appendi-
citis, leaving the need for diagnostic imaging or diagnostic
laparoscopy to the smaller group of patients with an
indeterminate scoring result.
Introduction
Acute appendicitis (AA) is a common condition and a fre-
quently suspected differential diagnosis in patients presenting
with acute abdominal pain. The diagnosis is often elusive and
the management of patients with an equivocal diagnosis is
controversial. Some advocate early surgical exploration on
wide indications hoping to prevent perforation, with an
associated high frequency of negative explorations as an
acceptable tradeoff [1]. Others propose early exploration in
patients with obvious disease and active observation of
patients with an equivocal diagnosis, which gives fewer
negative explorations without increasing the number of per-
forations [2–5]. In this latter approach it is important to detect
patients with advanced appendicitis early [6].
Imaging techniques such as ultrasound (US) and com-
puterized tomography (CT) and diagnostic laparoscopy
have been used with the hope of yielding a rapid and
accurate diagnosis. The main problems with routine use of
diagnostic imaging are potentially harmful ionizing radia-
tion (CT), examiner-dependent efficacy (US), and
technique-associated morbidity (diagnostic laparoscopy)
[7]. Diagnostic imaging performs less well in groups of
patients with low or high prevalence of disease in spite of
high sensitivity and specificity [8].
M. Andersson (&) Á R. E. Andersson
Department of Surgery, County Hospital Ryhov,
551 85 Jo¨nko¨ping, Sweden
e-mail: manne.andersson@lj.se
R. E. Andersson
Department of Surgery, University Hospital,
581 85 Linko¨ping, Sweden
123
World J Surg (2008) 32:1843–1849
DOI 10.1007/s00268-008-9649-y

2. The initial management of patients with suspected
appendicitis therefore still needs to be based on the disease
history, physical signs, and basic laboratory tests reflecting
the inflammatory response. This involves a subjective
synthesis of a large amount of complex information, which
relies on the surgeon’s knowledge and previous experience
with similar patients. This process could be improved by
using a clinical scoring system that can objectively deter-
mine the prognosis for the current patient from those of
similar patients from which the score was constructed. A
clinical scoring system can be used as a basis for a struc-
tured algorithm for the management of the patients,
including selective use of diagnostic imaging depending on
the probability of appendicitis.
A large number of scoring systems have been proposed.
The Alvarado score is the most well known and best per-
forming in validation studies [9, 10]. The Alvarado score
can be improved because it has some weaknesses. Its
construction was based on a retrospective review of
patients who had all been operated on for suspicion of
appendicitis, whereas the score is supposed to be used on
patients with suspicion of appendicitis. Because of the
difference in the spectrum of disease between these groups
of patients, the scoring weights may be biased [11]. The
variables were chosen without using an appropriate math-
ematical model to identify the variables with an
independent diagnostic value and to determine their scor-
ing weights. Finally, discriminating capacity was lost
because of the dichotomization of the variables.
The aim of this study was to construct and validate a
user-friendly clinical scoring system based on prospec-
tively collected data from patients admitted for suspected
appendicitis using an appropriate mathematic model
focused on detecting advanced appendicitis. It includes
inflammatory markers which have been shown to have high
discriminating power [12, 13]. Instead of dichotomous
variables, the clinical variables are graded according to the
severity of the symptoms and signs and the laboratory
variables are divided into intervals. Three diagnostic test
zones are defined: one with a high sensitivity for appen-
dicitis to identify the patients who can be safely discharged
with an outpatient followup, another with a high specificity
for appendicitis to identify patients who can be operated on
without further examination, and an indeterminate group of
patients who need additional diagnostic workup [14].
Patients and methods
Patients
Information on the disease history, clinical findings, and
results of laboratory tests was recorded for 502 consecutive
patients who were admitted for suspicion of appendicitis to
the hospitals in the towns of Jo¨nko¨ping and Eksjo¨ between
October 1992 and December 1993. Details about these
patients have been presented elsewhere [12]. Another 249
consecutive patients admitted to the hospitals La¨nssjukhuset
Ryhov in Jo¨nko¨ping, Ho¨glandssjukhuset in Eksjo¨, Lasarettet
in Motala, and La¨nssjukhuset in Kalmar during a 3-month
period in 1997 were also included. Of these 751 patients a
complete data set was available for 545 patients. The
remaining 206 patients were excluded because of missing
values of neutrophils (n = 154), pain migration (n = 37),
defense (n = 7), vomiting (n = 3), CRP (n = 2), anorexia
(n = 2), and body temperature (n = 1). The patients who
were excluded because of missing values had the same dis-
tribution of appendicitis diagnoses as the study patients but
were more often women (62 vs. 51%, p 0.009), had a
significantly higher proportion of negative appendectomies
(18 vs. 11%, p 0.009), and were older (median
age = 24.4 vs. 21.0 years, p 0.004). Although surgeons
with all levels of experience were involved, the majority of
patients admitted for suspicion of appendicitis were initially
evaluated by surgeons in training with limited experience.
All excised appendices were examined by microscopy.
The criterion for phlegmonous appendicitis was histopa-
thologic evidence of transmural inflammation and the
criterion for advanced appendicitis was histopathologic
evidence of transmural gangrene or perforation.
The nonoperated patients were followed up by a review
of their files, which is an accurate method of follow-up
according to the Swedish health care structure. None had
developed appendicitis at follow-up after 1 month. The
study was approved by the Human Ethical Committee at
Linko¨ping University Hospital.
Construction of the scores
Ordered logistic regression score
All included patients (n = 545) were randomly assigned a
value between 0 to 9. Patients with a value of 0–5
(n = 316) were used for the construction of the scoring
system and patients with a value of 6–9 (n = 229) were
used for validation of the scoring system. The variables in
the Alvarado score and a set of variables that were found to
have independent diagnostic importance for appendicitis in
a previous study [12] (right-lower-quadrant pain, pain
migration, muscular defense, rebound tenderness, WBC
count, proportion neutrophils, CRP, body temperature,
vomiting, anorexia, and gender) were included in an
ordered logistic regression analysis model, with the out-
come coded as 0 for no appendicitis, 1 for phlegmonous,
and 2 for advanced (i.e., gangrenous or perforated)
appendicitis. To optimize the discrimination of advanced
1844 World J Surg (2008) 32:1843–1849
123

3. appendicitis, we used weighted ordered logistic regression
models with the weight of 1 for no appendicitis, 2 for
phlegmonous appendicitis, and 5 for advanced appendici-
tis. Dummy variables were constructed for a large range of
intervals for the continuous variables. Adjacent intervals
with similar regression coefficients were successively
combined until a set of intervals with distinct and signifi-
cant regression coefficients was obtained. Variables and
intervals with a p 0.10 were kept in the final model [15].
The regression coefficients of the final, most parsimonious
model were used as scoring points.
Simplified score
A simplified score was constructed based on the regression
coefficients which were rounded up to the nearest integer,
except for pain in the right iliac fossa which had a
regression coefficient close to 1 and light rebound pain/
muscular defense, which were rounded down to obtain a
trend of increasing risk of appendicitis with increasing
intensity in this variable.
Validation of the scores
The scores were validated on the validation sample of 229
patients. The discriminating capacity of the scores was
compared with that of the Alvarado score from the ROC
areas. Separate analyses were done for the discrimination of
all appendicitis and for advanced appendicitis. Two cutoff
points were defined: one to obtain a high sensitivity for
advanced appendicitis and another with high specificity for
appendicitis. The sensitivity and specificity for all and for
advanced appendicitis were calculated for both cutoff points.
Statistical methods
Weighted ordered logistic regression analysis was used in the
construction of the scores to identify the variables with an
independent predicting capacity and to obtain the variables’
scoring weights. The ROC area was used for comparing the
discriminating capacity of the scores. Student’s t test, the v2
test, and Fisher’s exact test were used for analyzing differ-
ences in continuous variables and proportions. The
sensitivity and specificity of the new score were compared
with the Alvarado score using McNemars’ test. A p value of
less than 0.05 was regarded as significant. Patients with
phlegmonous appendicitis were excluded from the analyses
of the diagnostic value for advanced appendicitis.
Results
The construction and validation samples were similar with
regard to gender, prevalence of appendicitis, and Alvarado
score (Table 1). However, the patients in the construction
sample were older (mean age = 25.9 vs. 23.4 years for the
validation sample, p = 0.022). In total, 250 of the 545
patients underwent surgery. The prevalence of appendicitis
was 36 and 33% in the construction and validation samples,
and the prevalence of negative appendectomy was 11 and
10%, respectively.
Construction of the score
The regression coefficients of the weighted ordered logistic
regression analysis of the random sample of 316 patients
for the construction of the score are presented in Table 2.
Migration of pain, anorexia, and male gender were found to
have p [ 0.10 and were excluded from further analysis.
Eight variables reflecting the gastric upset, peritoneal irri-
tation and the inflammatory response (right-lower-quadrant
pain, vomiting, muscular defense, rebound tenderness,
WBC count, proportion neutrophils, CRP and body tem-
perature) remained in the final model. The simplified
integer-based score ranged from 0 to 12 points.
Validation of the score
The regression-based and the simplified scores were eval-
uated and compared with the Alvarado score on the
Table 1 Characteristics of the
patients in the construction and
validation samples
Characteristic Construction sample Validation sample p value
Number of patients 316 229
Men 145 (46%) 105 (46%)
Women 171 (54%) 124 (54%) 0.994
Mean age (years) 25.9 23.4 0.022
Number with appendicitis 115 (36%) 76 (33%)
Phlegmonous appendicitis 71 (22%) 46 (20%)
Advanced appendicitis 44 (14%) 30 (13%) 0.731
Number with negative appendectomy 36 (11%) 23 (10%)
Mean Alvarado score 5.1 5.2 0.735
World J Surg (2008) 32:1843–1849 1845
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4. validation sample of 229 patients. The discriminating
capacity of the scores is presented in Table 3. In all anal-
yses the simplified score performed at least as good as the
regression-based score. Therefore, the remaining results are
presented for the simplified score only. The score that was
constructed from the ordered logistic regression model
performed better in discriminating for advanced appendi-
citis compared with a score based on a logistic regression
model (data not shown).
The simplified score had a better discriminating capacity
for all appendicitis compared with the Alvarado score, with
ROC area of 0.93 vs. 0.88 (p = 0.0007). The same was
true for advanced appendicitis with ROC area of 0.97 vs.
0.92 for the Alvarado score (p = 0.0027). The perfor-
mance of the scores was similar in males and females
(Table 4). There was a nonsignificant trend toward a poorer
performance with increasing patient age (p = 0.058).
Two cutoff points were defined to obtain three diag-
nostic test zones: one with a high sensitivity for
appendicitis that could be used to rule out appendicitis, and
one with a high specificity for appendicitis that could be
used to rule in appendicitis. The results were compared
with the corresponding test zones for the Alvarado score
(Table 5).
The simplified score classified 144 of the 229 patients
(63%) to either the low- or the high-risk group with an
accuracy of 0.97 compared with 119 patients (52%) used
for the Alvarado score (p = 0.023) with an accuracy of
0.98. Eighty-five patients (37%) had an indeterminate
result with the simplified score compared with 110 patients
(48%) with the Alvarado score (p = 0.023).
Twenty-nine of the 229 patients (13%) were classified to
the high-risk group with more than 8 scoring points
(Table 5). This included 20 of the 30 patients with
advanced and 8 of the 46 patients with phlegmonous
appendicitis and 1 patient with nonoperatively treated
diverticulitis, giving a sensitivity of 0.37 and a specificity
of 0.99 for all appendicitis and a sensitivity of 0.67 and a
specificity of 0.99 for advanced appendicitis (Table 6). The
corresponding result for the Alvarado score was 23 patients
(10% of all patients, p = 0.42) of which 12 patients had
advanced and 9 patients had phlegmonous appendicitis, 1
Table 2 The new scores and the Alvarado score for comparison
Score Proposed score
Regression Simplified Alvarado
Relocation of pain ns - +1
Vomiting 0.45 +1 +1
Pain in RIF 1.12 +1 +2
Anorexia ns - +1
Male gender ns - -
Rebound tenderness or muscular defense
None 0 0 0
Light 1.54 +1 +1
Medium 1.90 +2 +1
Strong 2.32 +3 +1
Body temperature
37.5–37.9°C 0 0 +1
38.0–38.4°C 0 0 +1
C38.5°C 0.85 +1 +1
Proportion polymorphonuclear leukocytes
70–74% 0.92 +1 0
75–84% 0.92 +1 +1
C85% 1.41 +2 +1
WBC count
10.0–14.9 9 109
/L 0.96 +1 +2
C15.0 9 109
/L 1.46 +2 +2
CRP concentration
10–49 g/L 1.04 +1 -
C50 g/L 2.35 +2 -
Table 3 Discriminating capacity of the new scores compared with
the Alvarado score, according to the ROC areas
ROC area
Regression Simplified
Patients Alvarado Score p value Score p value
All appendicitis
Construction sample 0.868 0.913 0.003 0.913 0.0007
Validation sample 0.879 0.922 0.024 0.927 0.0007
Advanced appendicitis
Construction sample 0.912 0.965 0.0004 0.961 0.0004
Validation sample 0.924 0.962 0.037 0.972 0.0027
Table 4 Discriminating capacity of the simplified score compared to
the Alvarado score in subsets of the validation sample according to
the patients’ gender and age
ROC area
Patients Numbers Alvarado
score
Simplified
score
p
value
Gender
Men 105 0.850 0.917 0.0021
Women 124 0.914 0.935 0.27
p value, men vs. women 0.16 0.59
Age
0–12 years 49 0.925 0.977 0.13
13–29 years 124 0.892 0.925 0.053
30+ years 56 0.814 0.889 0.02
p value, between age
groups
0.25 0.058
1846 World J Surg (2008) 32:1843–1849
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5. patient with diverticulitis, and 1 with no pathology found,
giving a sensitivity of 0.28 (p = 0.07) and a specificity of
0.99 for all appendicitis and a sensitivity of 0.40
(p 0.005) and a specificity of 0.99 for advanced
appendicitis.
One hundred fifteen of the 229 patients (50%) were
classified to the low-risk group with less than 5 scoring
points (Table 5). There were three patients with phleg-
monous appendicitis giving an accuracy of 0.97. The
corresponding result for the Alvarado score was 96 patients
(42%) (p = 0.091) of which two patients had phlegmonous
appendicitis, giving an accuracy of 0.98. Of the nine neg-
ative appendectomies, there was one patient each with
salpingitis, retrograde menstruation, and ruptured ovarian
cyst, respectively, and two patients with omental torsion.
Of the 153 nonappendicitis patients, the simplified score
correctly classified 112 (73%) to the low-probability group
compared to 94 (61%, p 0.039) for the Alvarado score.
A score of greater than 4 points gave a similar sensitivity
for the simplified score and the Alvarado score (0.96 for all
and 1.00 for advanced appendicitis vs. 0.97 and 1.00,
respectively) but a higher specificity (0.73 vs. 0.61 irre-
spective of stage of disease, p 0.0007) (Table 6). This
corresponds to a negative predictive value of 0.97 for all
and 1.00 for advanced appendicitis at a score of less than 5
for the simplified score compared to 0.98 and 1.00,
respectively, for the Alvarado score. The positive predic-
tive value of a score greater than 8 was 0.97 for all
appendicitis and 0.95 for advanced appendicitis for the
simplified score and 0.91 and 0.86, respectively, for the
Alvarado score.
Discussion
The scoring system presented in this study could correctly
classify 73% of the nonappendicitis patients to the low-
probability group and 67% of the patients with advanced
appendicitis to the high-probability group with high accu-
racy. Only 37% of the patients remained in the
indeterminate group. This compares favorably with the
Alvarado score which gave 61, 40, and 48% for the cor-
responding results. This shows the potential of our clinical
scoring system to improve the clinical diagnosis of
appendicitis and to decrease the number of patients that
need in-hospital observation or further examination with
diagnostic imaging or diagnostic laparoscopy.
A clinical scoring system estimates the probability of
appendicitis in a patient compared with a large number of
similar patients from which the score was designed. This
information can be used for decision support for the less
experienced surgeon and may facilitate communication
between emergency room physicians and surgeons. A
clinical scoring system can also be the basis for a structured
management of patients with suspected appendicitis as
described in Table 7. Today it is common practice to
perform CT or US in all patients suspected of having
appendicitis. However, imaging does not perform well in
patients with low and high prevalence of the disease, and
CT should be used selectively to minimize exposure to
ionizing radiation [8]. Recent reports also suggest that the
indiscriminate use of CT scans may lead to the detection of
low-grade appendicitis that would otherwise have resolved
spontaneously [16–18].
A clinical score may therefore be a suitable instrument
for selecting patients for immediate surgery, observation at
Table 5 Distribution of patients according to the diagnostic test zone
and diagnosis for the simplified score and the Alvarado score
Diagnostic test zones
and diagnoses
Simplified
score
Alvarado
score
Score [ 8 = High probability 29 23
Advanced appendicitis 20 12
Phlegmonous 8 9
Negative appendectomy 1 2
Nonoperated 0 0
Score = 5–8 = Indeterminate
result
85 110
Advanced appendicitis 10 18
Phlegmonous 35 35
Negative appendectomy 13 12
Nonoperated 27 45
Score 5 = Low probability 115 96
Advanced appendicitis 0 0
Phlegmonous 3 2
Negative appendectomy 9 9
Nonoperated 103 85
Table 6 Diagnostic characteristics of the new simplified score
according to the cutoff points compared with the Alvarado score,
tested on the validation sample
Cutoff point
Simplified score Alvarado score
Diagnostic value [4 points [8 points [4 points [8 points
All appendicitis
Sensitivity 0.96 0.37* 0.97 0.28*
Specificity 0.73
0.99 0.61
0.99
PV+ 0.64 0.97 0.56 0.91
PV- 0.97 0.76 0.98 0.73
Advanced appendicitis
Sensitivity 1.00 0.67à
1.00 0.40à
Specificity 0.73
0.99 0.61 0.99
PV+ 0.42 0.95 0.34 0.86
PV- 1.00 0.94 1.00 0.89
* p = 0.07,
p 0.0007, à
p 0.005
World J Surg (2008) 32:1843–1849 1847
123

6. home, or further examination with imaging techniques. The
score can be repeated in equivocal cases during active
observation which improves the diagnostic accuracy [19,
20]. It can be used to monitor the evolution of the disease
in cases that are treated conservatively or that show signs
of spontaneous resolution. A clinical score can also be used
to describe the patients that are included in clinical studies
to facilitate the comparison of results.
The Alvarado score is the most well known and best
performing compared with others and performed well in
this study [10]. However, it has not gained wide acceptance
in everyday clinical practice probably because of an
insufficient discriminating capacity, although it has been
used in a number of prospective studies. The present score
is similar to the Alvarado score in many respects, but there
are important differences that may explain the better per-
formance. The Alvarado score was constructed using
retrospective material and univariate analysis, whereas our
score is based on prospectively collected data of variables
with independent prognostic value using a mathematically
more appropriate method for the construction. The unspe-
cific and subjective variables ‘‘anorexia,’’ ‘‘nausea,’’ and
‘‘relocation of pain’’ were exchanged for the more specific
and objective variables ‘‘vomiting,’’ CRP,’’ and ‘‘guard-
ing.’’ Less diagnostic information is lost by the use of
graded clinical findings and intervals of laboratory vari-
ables instead of dichotomization of variables. Many
surgeons of all levels of experience serving at four different
centers were involved in the collection of data. All these
features will probably increase the reproducibility and
generalizability of the score.
However, although the diagnostic data were collected
prospectively, a disturbingly high proportion of patients
had to be excluded because of missing data. One reason
was that at the time of the study the proportion of poly-
morphonuclear leukocytes had not been part of the routine
diagnostic workup, its diagnostic properties were not rec-
ognized, and the laboratory did not automatically deliver
this information. Today the neutrophil count is automati-
cally performed in most laboratories together with the
WBC count. We do not think that the scoring points for the
proportion of polymorphs is biased because the distribution
of missing values was random over the diagnoses.
To conclude, management of patients with suspected
acute appendicitis is still challenging and the optimal
management algorithm is still being debated even after the
introduction of CT, US, and diagnostic laparoscopy. This
study described the construction and evaluation of a simple
clinical scoring system that has a high discriminating
power, especially for advanced appendicitis. The score
outperforms the Alvarado score, which is currently the
most well-known scoring system. It can correctly classify
the majority of patients into those who can be sent home
for outpatient follow up or to be operated on immediately,
leaving a smaller number of patients with an indeterminate
result who are suitable for further investigation. The score
needs further evaluation in a prospective interventional
study, including external centers.
Acknowledgment This study was supported by the Jo¨nko¨ping
County Research Council.
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