Radiol Oncol 2023; 57(4): 524-529. doi: 10.2478/raon-2023-0060
524
research article
Phase angle as a prognostic indicator 
of surgical outcomes in patients with 
gastrointestinal cancer
Jana Gulin
1
, Ester Ipavic
1
, Denis Mlakar Mastnak
2
, Erik Brecelj
2
, Ibrahim Edhemovic
2
, 
Nada Rotovnik Kozjek
2,3
1 
Medical Centre Ljubljana, Ljubljana, Slovenia
2
 Institute of Oncology Ljubljana, Ljubljana, Slovenia
3
 University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
Radiol Oncol 2023; 57(4): 524-529.
Received 3 August 2023 
Accepted 30 September 2023
Correspondence to: Asst. Prof. Nada Rotovnik Kozjek, M.D., Ph.D., Institute of Oncology Ljubljana, Zaloška 2, SI-1000 Ljubljana, Slovenia. 
E-mail: nkozjek1@gmail.com.
Disclosure: No potential conflicts of interest were disclosed. 
This is an open access article distributed under the terms of the CC-BY license (https://creativecommons.org/licenses/by/4.0/).
Background. In patients with gastrointestinal cancer with planned elective surgery, malnutrition increases the risk of 
adverse outcomes in the postoperative period. The phase angle, measured by the bioelectrical impedance analysis 
is an indicator of the metabolic and functional status of the patient. It may be an important prognostic indicator for 
the clinical outcome of post-surgical treatment in patients with gastrointestinal cancer.
Patients and methods. In this prospective study, 70 patients with gastrointestinal cancer had their phase angles 
measured by the bioelectrical impedance analysis before the surgery. During the first month after the surgery, we 
documented the postoperative complications from the patient’s records and classified them according to the 
Clavien Dindo classification of surgical complications. The time of hospitalization was also recorded. The data was 
statistically analysed in SPSS.
Results. We found a statistically significant difference (p = 0.036) in the average value of phase angles between the 
group of patients who had postoperative complications (phase angle 5.09°) and the group without postoperative 
complications (5.64°). We noted a correlating trend of decreasing phase angle values and increasing hospitalization 
time (Pe R = –0,40, p = 0,001). The phase angle cut-off value (5.5°) was calculated using the ROC curve method, pre-
dicting a higher risk of the postoperative complications (p = 0,037) in patients with lower phase angle.
Conclusions. Lower phase angle values before surgery were associated with more complications during the first 
month after surgery and longer hospitalization time. We found that a phase angle below than 5.5° could serve as a 
marker that predicts a greater risk of postoperative complications.
Key words: phase angle; colorectal cancer; postoperative complications; malnutrition
Introduction
Bioelectric Impedance Analysis (BIA) is a tech-
nique used to assess body composition and is be-
coming increasingly established as a tool to assess 
nutritional status in patients due to its ease of use, 
low cost, and non-invasiveness.
1,2
 BIA does not di-
rectly measure the body composition, but instead 
measures the drop in voltage of an alternating 
electric current, as it travels across the body. The 
phase angle is the quotient of measured resistance 
and reactance.
1-4
 It is interpreted as an indicator 
of membrane integrity and water distribution be-
tween the intracellular and extracellular spaces. 

Radiol Oncol 2023; 57(4): 524-529.
Gulin J et al. / Phase angle as a prognostic indicator of surgical outcome 525
Phase Angle is used to evaluate body cell mass, 
which serves as a tool to assess nutritional status 
in adults and children. Lower phase angle sug-
gests cell degradation with a concomitant decrease 
in overall cell number with reduced integrity and 
functional capacity of cell membranes. On the oth-
er hand, higher phase angle points to the presence 
of more functional, intact cell membranes.
5-9
 
Malnutrition is a common manifestation of ad-
vanced stage cancer and can severely affect the pa-
tient morbidity and mortality.
10
 On a cellular level 
malnutrition is reflected by the diminished integ-
rity of the cell membranes and by altered water 
distribution throughout the body.
11
 Body compo-
sition analysis is therefore an essential tool in as-
sessing nutritional status in cancer patients.
12
 The 
clinical role of measuring the patient’s phase angle 
is becoming progressively more important. BIA-
derived phase angle can help establish guidelines 
for preventive and supportive measures in patients 
with malnutrition, as it allows for early identifica-
tion of high-risk patients with inadequate physi-
ological reserves. The method has previously been 
shown to have prognostic value in patients with 
liver cirrhosis, haemodialysis, cancer, HIV/AIDS 
infection, and lung disease.
5,13-18
 For example, pa-
tients with stage III or IV colorectal cancer who 
had a phase angle less than or equal to 5.57° had 
a median survival of 8.6 months, while those who 
had a phase angle greater than 5.57° had a median 
survival of 40.4 months.
14
 
The primary objective of this study was to de-
termine if the phase angle can be useful as an inde-
pendent predictor of post-surgical complications 
in gastrointestinal cancer patients.
Patients and methods
Setting and patients
Our study was a prospective observational study 
that was performed at the Institute of Oncology 
Ljubljana, Slovenia, between November 2018 and 
February 2019. During the study period, BIA was 
performed on every gastrointestinal cancer patient 
over 18 years of age that was admitted for elective 
surgery at the Institute of Oncology Ljubljana and 
agreed to participate in the study. Exclusion criteria 
were pregnancy or an implanted pacemaker. The 
study protocol was approved by the Ministry of 
Health Medical Ethics Committee and the Institute 
of Oncology (No. 0120-518/2018/7). Every included 
patient was fully informed of the study design and 
signed a written informed consent form. 
Bioelectrical Impedance Analysis (BIA) 
and other measurements
BIA was performed with a Bodystat (R) Quadscan 
4000 machine (Douglas, UK). This phase-sensitive 
BIA device uses an alternating current of 0.8 mA 
with frequencies of 5, 50, 100, and 2000 kHz to 
measure the body impedance. The BIA-derived 
phase angle was calculated from the impedance at 
100 kHz.
Every patient had their phase angle measured 
the day before surgery and then a week and a 
month after the surgery. The patients were in-
structed to abstain from eating and drinking for 
at least 4 hours prior to the measurement and to 
abstain from any physical exercise for 8 hours pri-
or to the measurement as well. Two pairs of elec-
trodes were placed on the dorsal side of their right 
hand and right foot, and they were instructed to 
lie still in a supine position with no parts of the 
body touching one another. Clinical data, includ-
ing gender, age, the exact location of malignant 
disease, complications in the postoperative course, 
and hospitalization time were obtained from the 
hospital information system.
Clavien Dindo Classification of surgical 
complications
The patients were categorized in different grades 
of the Clavien Dindo classification of surgical 
complications (revised 2004).
19
 The classification 
uses the degree of most severe pharmacological 
or surgical treatment needed after surgery, to dis-
tinguish between the grades of post-surgical com-
plications. A normal postoperative course without 
any complications (use of analgesics is considered 
as normal postoperative course) is classified as de-
gree 0. Degree 1 allows the use of antiemetics, an-
tipyretics, potent analgesics, diuretics, physiother-
apy, and treatment of wound infections. Degree 2 
additionally includes the use of other drugs, blood 
transfusion, and total parenteral nutrition. Degree 
3 allows surgical, endoscopic, or radiological inter-
ventions. Degree 4 includes life-threatening com-
plications that require treatment in an intensive 
care setting. Fatal complications are classified as 
a degree 5.
Statistics
Numeric variables are expressed in terms of 
their mean values and a 95% confidence interval. 
Discrete variables are expressed as percentages. 

Radiol Oncol 2023; 57(4): 524-529.
Gulin J et al. / Phase angle as a prognostic indicator of surgical outcome 526
The Shapiro-Wilk test was used to check wheth-
er the data is normally distributed. The limit for 
statistical significance was set at p < 0.05. Logistic 
regression was used to test whether the initial pre-
operative phase angle, as an independent variable, 
impacts the odds of post-surgical complications. 
The results are expressed as quotients. A cut-off 
value for the phase angle as a predictive factor for 
post-surgical complications was estimated with a 
ROC curve, and its sensitivity and specificity were 
calculated. The statistical analysis was done with 
the IBM SPSS 23.0 statistical program.
Results 
During the study period (between November 2018 
and February 2019), BIA analysis was performed 
on every gastrointestinal cancer patient planned 
for elective surgery at the Institute of Oncology 
Ljubljana that agreed to participate in the study. 
Seventy patients were recruited. Characteristics of 
the included patients (column 1), of patients with-
out any complications (column 2) and patients with 
complications (column 3) are presented in Table 1. 
The mean age of all patients was 65.0 ± 10.7 years, 
and 71% were male. Most patients were admitted 
because of rectal cancer (64.3%). Mean phase angle 
of all patients was 5.23° ± 2.77°. In total, 52 (74,3%) 
patients had a complication (Clavien Dindo grade 
1-5) after surgery (Table 1 and Table 2).
Phase angle and the likelihood of 
complications
The phase angle of patients without a complication 
was significantly higher than that of the patients 
with a complication (5.64° ± 0.72° vs. 5.09° ± 0.98°, 
p = 0.036). Univariate logistic regression analysis 
showed that the phase angle was associated with 
the likelihood of a complication (phase angle: odds 
ratio = 0.48). The odds of a complication in a patient 
with a phase angle of 5.0 was 3.83, whereas it was 
only 1.84 in a patient with a phase angle of 6.0. The 
probabilities of the occurrence of a complication 
at different phase angles were calculated and are 
shown in Table 3. The area under the curve (AUC) 
of the ROC curve for phase angle for the likeli-
TABLE 1. Characteristics of patients
Characteristics All patients
Patients with no
complications (G0)
Patients with
complications (G1–G5)
p-value
Gender
    Male 50 (71 %)
    Female 20 (29 %)
Age (years)
a
65.0 (10.7)
[62.4 – 67.6]
61.7 (9.8)
[56.9–66.6]
66.1 (10.9)
[63.1– 69.2]
0.137
Phase Angle (°)
a
5.23 (2.77)
[5.0–5.5]
5.64 (0.72)
[5.3–6.0]
5.09 (0.98)
[4.8–5.4]
0.036*
Location of the primary tumor (%)
    Colon 17 (24,3) 4 (22.2) 13 (25.0)
    Rectosigmoid 2 (2,9) 1 (5.5) 1 (1.9)
    Rectum 45 (64,3) 11 (61.1) 34 (65.4)
    Anus 1 (1,4) 1 (5.5) 0 (0)
    Breast 1 (1,4) 0 (0) 1 (1.9)
    Ovary 4 (5,7) 1 (5.5) 3 (5.8)
a 
Arithmetic mean (standard deviation) [confidence interval].
* Statistically significant p-value
TABLE 2. Mean age and mean phase angle in each Clavien Dindo grade
Number of 
patients (%)
Age (years) a Phase angle (°)
a
Grade 0 18 (26) 61.7 [56.9–66.6] 5.64 [5.28–6.00]
Grade I 5 (7) 56.0 [50.2–61.8] 6.22 [5.64–6.80]
Grade II 38 (54) 67.1 [63.4 –70.7] 4.99 [4.67–5.31]
Grade III 4 (6) 62.2 [45.0 –79.5] 5.15 [3.41–6.88]
Grade IV 5 (7) 72.2 [60.5–83.9] 4.64 [3.77–5.51]
Grade V 0 (0)
a 
Arithmetic mean (standard deviation) [95% confidence interval].

Radiol Oncol 2023; 57(4): 524-529.
Gulin J et al. / Phase angle as a prognostic indicator of surgical outcome 527
6.0°, the odds of a complication are reduced to 1.84, 
and the likelihood of a complication is reduced to 
64.8%. 
We are not aware of any prospective studies in-
vestigating the role of phase angle as a prognostic 
indicator of post-surgical complications in colorec-
tal cancer patients. The retrospective data analysis 
from 210 elderly patients (aged ≥ 65 years) under-
going gastrectomy showed that preoperative low 
phase angle predicts a higher risk of postoperative 
complications.
20
 Similar observations were made 
in a study among patients admitted to the ICU, 
where phase angle at admission was shown to be 
a predictor of 90-day mortality. The mean phase 
angle of survivors was significantly higher than 
that of the non-survivor group (5.0° ± 1.3° versus 
4.1° ± 1.2°, p < 0.001).
21
 In a study that compared 
outcomes after cardiothoracic surgery between a 
group of low phase angle (< 5.38°) patients and a 
group of normal phase angle patients, the partici-
pants from the first group had a higher number 
of post-operative infections, a larger percentage 
of them were ventilated for more than 12 hours, 
and had higher rates of mortality. However, after 
considering other parameters like sex, age, the 
type of operative procedure, risk assessment, in-
flammation activity, hypoalbuminemia, heart fail-
ure, time of cardiopulmonary bypass, and time of 
aortic cross-clamp, the phase angle was found not 
to be statistically significant in correlation with 
aforementioned complications. Still, the difference 
between the groups stayed statistically significant 
in regard to the hospitalization time and the time 
spent in the intensive care unit.
22
FIGURE 1. The ROC curve for the phase angle.
TABLE 3. Odds for developing a complication and probabilities of developing a 
complication at different values of phase angle
Phase Angle (°)
Odds of a  
complication
Probability of a 
complication (%)
4.5 5.532 84.7
5.0 3.831 79.3
5.5 2.651 72.6
6.0 1.837 64.8
TABLE 4. Contingency Table with the sensitivity and a specificity of the phase 
angle
Phase angle < 5,5 Phase angle ≥ 5,5
Complication 33 (true positive) 19 (false negative) 52
No complication 7 (false positive) 11 (true negative) 18
40 30
hood of a complication is 0.666 (CI: 0.529 - 0.803, p = 
0.037), see Figure 1. The determination coefficient 
(Nagelkerke R square) is 0.104, which means that 
our model explains 10.4% of the complication like-
lihood variance. The Hosmer and Lemeshow test 
value for the model is 0.766.
The optimal cut-off value for the phase 
angle
The cut-off value of phase angle that was derived 
from the ROC-curve was 5.5° (Figure 1). It yielded a 
sensitivity of 63% and a specificity of 61% (Table 4). 
The likelihood of a complication was higher in pa-
tients with phase angle below 5.5° than in the pa-
tients with phase angle above that value (82.5% vs. 
63.3%, Figure 1).
Discussion
The patients with a lower initial phase angle were 
shown to have a statistically significant higher 
likelihood of post-surgical complications. The 
mean phase angle in the group with complications 
(5,64°) was statistically higher than the mean phase 
angle in the group without complications (5,09°). 
We used univariate logistic regression to cal-
culate the likelihood of a complication at different 
initial phase angle values. At a phase angle of 5.0°, 
the odds of a complication are 3.83, and the likeli-
hood of a complication is 79.3%. At a phase angle of 

Radiol Oncol 2023; 57(4): 524-529.
Gulin J et al. / Phase angle as a prognostic indicator of surgical outcome 528
In addition, we aimed to find a cut-off phase an-
gle value that can be used to identify high-risk pa-
tients that are more likely to have a severe compli-
cation after gastrointestinal cancer surgery. Using 
5.5° as a cut-off value, we were able to successfully 
identify these patients in in 67% of the cases with a 
sensitivity of 63% and a specificity of 61%. 
Different phase angle cut-off values have ap-
peared in literature to identify patients with lower 
physiological reserves who are at risk for increased 
morbidity and mortality. The proposed PA values 
in literature are 5.5° for patients newly admitted to 
the hospital
23
, 4.73° for patients newly diagnosed 
with head and neck cancer
24
, and 5.2° for patients 
with various cancers before starting radiother-
apy
25
. The phase angle values put forward as a 
predictor of survival were 4.5° for patients with a 
non-small cell lung cancer
15
, 5.0° for patients with 
advanced pancreatic cancer
26
, 5.4° for patients with 
liver cirrhosis
5
, and 5.57° for patients with colon 
and rectum cancer
14
. 
One of the limitations of this study is a relative-
ly heterogeneous group of patients. The patients 
included in our study had cancer in different loca-
tions and stages in abdomen and they were under-
going different treatment protocols. Additionally, 
our analysis only took into account the pre-opera-
tive value of the phase angle. The patients’ phase 
angle might have changed in the peri-operative 
period, especially on account of nutritional sup-
port or further medical interventions. Therefore, 
the value might not have been representative of 
the patients overall physical state within the entire 
observed period. The obtained cut-off phase angle 
value of 5.5° needs to be considered as a tentative 
value as it was calculated using a specific sample 
in one population. Further research is needed to 
identify the cut-off value for different subtypes of 
colorectal cancer and to evaluate the validity of 
our obtained cut-off value in distinct clinical set-
tings. 
The primary clinical implication of this study 
is that the phase angle measurement can assist in 
identifying GI cancer patients with a higher risk 
of post-operative complications. This could benefit 
patients that would otherwise not have been iden-
tified. Further research is needed to investigate 
if nutritional or other medical interventions can 
significantly alter the phase angle and thus affect 
surgical outcomes.
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