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Original Article
CRC
 Impact of iron-deficiency anemia on short-term outcomes after resection of colorectal cancer liver metastasis: a US National (Nationwide) Inpatient Sample (NIS) analysis
Ko-Chao Lee1,2,3orcid, Yu-Li Su4orcid, Kuen-Lin Wu1orcid, Kung-Chuan Cheng1orcid, Ling-Chiao Song5orcid, Chien-En Tang1orcid, Hong-Hwa Chen1orcid, Kuan-Chih Chung6orcid
Annals of Coloproctology 2025;41(2):119-126.
DOI: https://doi.org/10.3393/ac.2024.00591.0084
Published online: April 24, 2025

1Division of Colorectal Surgery, Department of Surgery, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kaohsiung, Taiwan

2Division of Colorectal Surgery, Department of Surgery, Kaohsiung Municipal Fong Shan Hospital (under the management of Chang Gung Medical Foundation), Kaohsiung, Taiwan

3Division of Colorectal Surgery, Department of Surgery, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung, Taiwan

4Division of Hematology Oncology, Department of Internal Medicine, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kaohsiung, Taiwan

5Division of Colon and Rectal Surgery, Department of Surgery, E-DA Hospital, I-Shou University, Kaohsiung, Taiwan

6Department of Anesthesiology, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kaohsiung, Taiwan

Correspondence to: Kuan-Chih Chung, MD Department of Anesthesiology, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, No. 123, Dapi Rd, Niaosong District, Kaohsiung 83301, Taiwan Email: s21096@cgmh.org.tw
• Received: September 3, 2024   • Revised: December 27, 2024   • Accepted: December 30, 2024

© 2025 The Korean Society of Coloproctology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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  • Purpose
    Colorectal cancer (CRC) often spreads to the liver, necessitating surgical treatment for CRC liver metastasis (CRLM). Iron-deficiency anemia is common in CRC patients and is associated with fatigue and weakness. This study investigated the effects of iron-deficiency anemia on the outcomes of surgical resection of CRLM.
  • Methods
    This population-based, retrospective study evaluated data from adults ≥20 years old with CRLM who underwent hepatic resection. All patient data were extracted from the 2005–2018 US National (Nationwide) Inpatient Sample (NIS) database. The outcome measures were in-hospital outcomes including 30-day mortality, unfavorable discharge, and prolonged length of hospital stay (LOS), and short-term complications such as bleeding and infection. Associations between iron-deficiency anemia and outcomes were determined using logistic regression analysis.
  • Results
    Data from 7,749 patients (representing 37,923 persons in the United States after weighting) were analyzed. Multivariable analysis revealed that iron-deficiency anemia was significantly associated with an increased risk of prolonged LOS (adjusted odds ratio [aOR], 2.76; 95% confidence interval [CI], 2.30–3.30), unfavorable discharge (aOR, 2.42; 95% CI, 1.83–3.19), bleeding (aOR, 5.05; 95% CI, 2.92–8.74), sepsis (aOR, 1.60; 95% CI, 1.04–2.46), pneumonia (aOR, 2.54; 95% CI, 1.72–3.74), and acute kidney injury (aOR, 1.71; 95% CI, 1.24–2.35). Subgroup analyses revealed consistent associations between iron-deficiency anemia and prolonged LOS across age, sex, and obesity status categories.
  • Conclusion
    In patients undergoing hepatic resection for CRLM, iron-deficiency anemia is an independent risk factor for prolonged LOS, unfavorable discharge, and several critical postoperative complications. These findings underscore the need for proactive anemia management to optimize surgical outcomes.
  • Keywords: Colorectal neoplasms; Neoplasm metastases; Iron-deficiency anemia; Postoperative complications
Colorectal carcinoma (CRC) is the third most common cancer worldwide [1, 2]. Due to the portal circulation between the colon and liver, the liver is the most frequently observed site of CRC metastasis [3]. Approximately 15% to 25% of CRC patients have distant metastases at the time of the primary diagnosis [4], and an additional 18% to 25% of patients may develop distant metastasis within 5 years of diagnosis [5]. Surgery, whether performed through open or laparoscopic techniques, remains the predominant treatment method for CRC liver metastasis (CRLM) [6].
Iron-deficiency anemia occurs when the body lacks enough iron to produce an adequate amount of hemoglobin, which is crucial for efficient oxygen transport [7]. Between 30% and 60% of CRC patients develop iron-deficiency anemia, mainly due to chronic blood loss and inflammation linked to the cancer. This condition leads to functional iron deficiency by increasing the levels of hepcidin, a hormone that inhibits iron absorption in the duodenum [8, 9].
Fatigue and weakness are common symptoms of iron-deficiency anemia [10]. Furthermore, this condition has been established as a risk factor for unfavorable postsurgical outcomes, including higher rates of infection, prolonged hospitalization, circulatory overload, and increased mortality and morbidity [11]. This issue is particularly concerning in the context of major surgery, such as the operations performed for CRLM, where optimal tissue oxygenation is critical for postoperative recovery. Hemoglobin, an essential component of red blood cells, plays a pivotal role in delivering oxygen to tissues and supporting immune function, both of which are crucial for wound healing and infection control [12]. Given that surgery for CRLM is often complex and involves extensive tissue manipulation, the increased oxygen demand during both the intraoperative and postoperative phases is particularly relevant. Patients with iron-deficiency anemia may not have the necessary hemoglobin levels to meet these demands, which can result in suboptimal outcomes. Furthermore, the high-risk nature of CRLM patients, many of whom may already have compromised immune function or other comorbidities, makes them particularly vulnerable to the adverse effects of anemia. Despite its importance, however, research on this issue remains limited.
This retrospective study investigated the association between iron-deficiency anemia and surgical outcomes in patients with CRLM using data from the US National (Nationwide) Inpatient Sample (NIS) database.
Ethics statement
The study protocol was approved by Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine (No. 202401647B0B1). The study conforms to the data-use agreement for the NIS from the Healthcare Cost and Utilization Project (HCUP) [13]. Permission to use the database was obtained from HCUP-NIS (No. HCUP-4X38L41JU). Because the NIS originally received signed informed consent from all included patients to participate in data collection for later evaluation, and patient data in the NIS database were subsequently de-identified, the requirement for signed informed consent was waived for the present study.
Study design and data source
This was a cross-sectional, population-based retrospective study that analyzed inpatient data collected at patient discharge by the HCUP-NIS administrative database from 2005 to 2018. Data for this study were extracted from the 2005–2018 NIS database, which was developed by the HCUP and is maintained by the US Agency for Healthcare Research and Quality [13]. The NIS database represents a 20% sample of inpatient admissions from 45 states and 1,051 hospitals that participate by collecting patient data at discharge. Principal and secondary diagnoses, principal and secondary procedures, admission date and diagnosis, discharge status, patient demographic data, and length of hospital stay (LOS) are included for each inpatient. The NIS also provides statistical weights that enable generalized estimates of national case volumes.
Study population
Data from patients >20 years old diagnosed with CRLM who received hepatic resection were included in the analysis. Patients without information on sex and/or with incomplete information on the outcome measures were excluded. Surgical procedures and diagnoses were identified using the International Classification of Diseases, 9th and 10th Revision, Clinical Modification (ICD-9-CM and ICD-10-CM) codes. The included patients were separated into 2 groups based on whether or not they had iron-deficiency anemia (ICD-9-CM code 280.x and ICD-10-CM code D50.x). The other codes used in this study are listed in Supplementary Table 1.
Main outcomes and variables
The main outcome measures were in-hospital outcomes and short-term complications. In-hospital outcomes included in-hospital mortality, unfavorable discharge (not discharged to home), and prolonged LOS. Short-term postoperative complications included stroke, biliary leaks, bleeding, sepsis, system infections, pneumonia, respiratory failure/mechanical ventilation, fever, nausea, and abdominal pain, acute liver failure, acute kidney injury, and urinary tract infection.
The demographic data extracted from the records included patient age, sex, ethnicity (grouped by NIS into White, Black, Hispanic, and others), household income, insurance status/primary payer, weekend admission, and lifestyle factors of smoking and obesity status. Hospital-related variables included hospital bed size and hospital location/teaching status.
Statistical analysis
Descriptive statistics for the patients were presented as unweighted counts (n) and weighted percentage (%) or mean±standard error. Since the NIS database covers 20% of the US annual inpatient admissions, weighted samples, strata, and clusters were used to produce national estimates for all analyses. The P-value for group comparisons was calculated for categorical and continuous data. Logistic regression models were performed to identify the risk for in-hospital mortality, prolonged LOS, unfavorable discharge, and short-term complications in patients with iron-deficiency anemia. Prolonged LOS was defined as a hospital LOS longer than the 75th percentile of the study population. Multivariable regression was adjusted for related variables with a value of P<0.05 in univariate analysis (except for surgical type). Stratified analyses were performed based on patients’ age, sex, and obesity status. All P-values were 2-sided, and a P-value of <0.05 was considered statistically significant. All statistical analyses were performed using SAS ver. 9.4 (SAS Institute Inc).
Study population selection
The study population selection process is depicted in Fig. 1. In total, 7,766 hospitalized patients aged >20 years old with CRLM who underwent hepatic resection were identified in the NIS database from 2005 to 2018. Twelve patients with missing information on sex and study outcomes were excluded. We further excluded 5 patients without the weight values of the dataset. Finally, a total of 7,749 patients were included in the analysis. This sample represents 37,923 hospitalized patients in the entire United States after weighting.
Characteristics of patients with CRLM
Patient outcomes, demographic characteristics, and hospital-related information are summarized in Table 1. The mean age of all patients was 59.6 years. Furthermore, 4,360 patients (56.3%) were male, and 3,880 (50.1%) had insurance from private companies or health maintenance organizations. Patients diagnosed with iron-deficiency anemia had higher percentages of prolonged LOS, unfavorable discharge, bleeding, sepsis, pneumonia, and acute kidney injury than their counterparts without anemia.
Associations between iron-deficiency anemia and outcomes in patients with CRLM undergoing liver resection
Multivariable analysis showed that iron-deficiency anemia was significantly associated with an increased risk of prolonged LOS (adjusted odds ratio [aOR], 2.76; 95% confidence interval [CI], 2.30–3.30; P<0.001) and unfavorable discharge (aOR, 2.42; 95% CI, 1.83–3.19; P<0.001) than patients without anemia. Iron-deficiency anemia was also significantly associated with higher odds of bleeding (aOR, 5.05; 95% CI, 2.92–8.74; P<0.001), sepsis (aOR, 1.60; 95% CI, 1.04–2.46; P=0.032), pneumonia (aOR, 2.54; 95% CI, 1.72–3.74; P<0.001), and acute kidney injury (aOR, 1.71; 95% CI, 1.24–2.35; P=0.001) (Table 2).
Associations between iron-deficiency anemia and outcomes, stratified by age, sex, and obesity status
Subgroup analyses between iron-deficiency anemia and outcomes, stratified by age, sex, and obesity status are shown in Table 3. Further analyses stratified by age, sex, and obesity revealed that iron-deficiency anemia was significantly associated with prolonged LOS across all subgroups. Iron-deficiency anemia was significantly associated with higher odds of prolonged LOS among patients aged <60 years (aOR, 1.84), ≥60 years (aOR, 1.97), men (aOR, 2.02), women (aOR, 1.79), obese individuals (aOR, 2.29), and nonobese individuals (aOR, 1.85), with all P-values of <0.001.
Compared to patients without iron-deficiency anemia, those with the condition had a significantly higher risk of bleeding across all subgroups except the obese group. The aOR was 3.43 for patients <60 years, 3.46 for those ≥60 years, 3.97 for men, 3.12 for women, and 3.61 for nonobese patients.
Iron-deficiency anemia was significantly associated with pneumonia across all subgroups except obese patients. The aOR was 2.34 for patients <60 years, 1.74 for those ≥60 years, 1.75 for men, 2.24 for women, and 1.90 for nonobese patients.
Further, iron-deficiency anemia was significantly associated with an increased risk of unfavorable discharge among 3 subgroups: patients <60 years (aOR, 4.80), men (aOR, 1.69), and obese patients (aOR, 2.81).
In patients hospitalized for liver resection for CRLM, preoperative iron-deficiency anemia was independently associated with worse in-hospital outcomes, including prolonged LOS, unfavorable discharge (discharge to long-term facility of survivors), bleeding, sepsis, pneumonia, and acute kidney injury. These findings highlight the need for proactive management of anemia in these patients to reduce in-hospital complications.
Up to 40% of patients undergoing major surgery have preoperative anemia, and anemia is an independent risk factor for the need for blood transfusion, morbidity, and mortality [14]. In nonemergent surgical cases, it is advisable to address anemia through iron supplementation or the use of erythropoiesis-stimulating agents, reserving red blood cell transfusions for essential situations only [15, 16]. Research indicates that managing anemia before surgery can lead to better patient outcomes [15, 16]. Additionally, a recent systematic review found that intravenous iron therapy significantly and rapidly increased hemoglobin levels in patients with preoperative anemia who were undergoing abdominal surgery [17].
Approximately 50% of patients with CRC develop CRLM, which is the leading cause of CRC-related deaths [18]. Although various treatments are available, such as radiofrequency ablation, metastasectomy remains the most effective option when feasible [18]. Approximately 20% of patients with CRLM who undergo metastasectomy achieve a cure, and roughly 50% survive for at least 5 years [18]. For patients initially deemed ineligible for metastasis removal, multimodal therapies—including chemotherapy for downstaging prior to surgery and locoregional treatments—have significantly improved outcomes [19].
While limited studies have focused on anemia in CRLM, several have examined its impact on the outcomes of CRC surgery [20–23]. A systematic review and meta-analysis published in 2017 examined the prognostic value of preoperative anemia in patients with CRC [21]. Another study of 35,000 colon cancer patients who underwent colectomy found that 50% had preoperative anemia, leading to higher rates of 30-day complications and mortality, although regression analysis showed that anemia was independently linked only to an elevated risk of 30-day complications [23].
An additional study by Gvirtzman et al. [22] suggested anemia could predict CRC prognosis, finding that advanced CRC stages correlated with severe anemia. Long et al. [20] analyzed 2,018 patients with CRLM and found that chronic anemia, emergency admissions, and hepatic lobectomy were associated with higher transfusion needs, which increased in-hospital mortality, complications, and LOS. Moreover, some research has suggested that the presence of anemia can predict the presence of CRLM. Heedman et al. [24] reported that 41% of CRC patients with metastasis had anemia at presentation, while Sala et al. [25] found that CRC patients with CRLM were more likely to develop anemia in the 3 months prior to diagnosis than those without CRLM.
In conclusion, this study, along with prior research, underscores the significant impact of iron-deficiency anemia on CRLM management. Addressing anemia before surgery is crucial for improving surgical outcomes and survival among patients with CRLM.
Strengths and limitations
This population-based study analyzed secondary data from a large and nationally representative patient database. A notable strength of the study is that its conclusions are applicable to the general population. However, the study's retrospective and observational design inherently limits the generalizability of the results to other populations and does not eliminate the possibility of selection bias. Like other studies utilizing ICD code systems, this study may also be susceptible to coding errors in data recording. Additionally, due to the focus on in-hospital outcomes, the study does not include data on clinical laboratory parameters or long-term follow-up data post-discharge.
Conclusions
In US patients who receive surgery for CRLM, iron-deficiency anemia was associated with a higher risk of prolonged LOS, unfavorable discharge, and several postoperative complications, including bleeding, pneumonia, sepsis, and acute kidney injury. Future research should focus on prospective clinical trials to evaluate the effectiveness of anemia management strategies, such as preoperative iron supplementation, in improving surgical outcomes in this population.

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Author contributions

Conceptualization: KCL, YLS, KLW, KC Cheng, LCS, CET; Data curation: KCL, YLS, KLW, KC Cheng, LCS, CET, HHC; Formal analysis: all authors; Methodology: KCL, YLS, KLW, KC Cheng, LCS, CET; Supervision: KCL, YLS; Validation: KCL, YLS; Writing–original draft: KCL, YLS, KC Chung; Writing–review & editing: KLW, KC Cheng, LCS, CET, HHC, KC Chung. All authors read and approved the final manuscript.

Supplementary Table 1.

ICD codes utilized in the analyses
ac-2024-00591-0084-Supplementary-Table-1.pdf
Supplementary materials are available from https://doi.org/10.3393/ac.2024.00591.0084.
Fig. 1.
Flowchart of study population selection. HCUP, Healthcare Cost and Utilization Project; NIS, National (Nationwide) Inpatient Sample. aThis sample represents 37,923 hospitalized patients in the entire United States after weighting.
ac-2024-00591-0084f1.jpg
Table 1.
Patient demographic characteristics and in-hospital outcomes
Characteristic Total (n=7,749) Iron-deficiency anemia
 P-value
Yes (n=446) No (n=7,303)
Age (yr) 59.6±0.2 62.1±0.5 59.5±0.2 <0.001*
 20–29 77 (1.0) 1 (0.2) 76 (1.0) <0.001*
 30–39 356 (4.6) 21 (4.7) 335 (4.6)
 40–49 1,151 (14.9) 56 (12.6) 1,095 (15.0)
 50–59 2,293 (29.6) 111 (24.9) 2,182 (29.9)
 60–69 2,071 (26.7) 122 (27.4) 1,949 (26.7)
 70–79 1,394 (18.0) 93 (20.9) 1,301 (17.8)
 ≥80 407 (5.3) 42 (9.4) 365 (5.0)
Sex <0.001*
 Male 4,360 (56.3) 212 (47.5) 4,148 (56.8)
 Female 3,389 (43.7) 234 (52.5) 3,155 (43.2)
Insurance status 0.001*
 Medicare/Medicaid 3,415 (44.1) 231 (51.8) 3,184 (43.6)
 Private including health maintenance organization 3,880 (50.1) 186 (41.7) 3,694 (50.6)
 Self-pay, no-charge, or other 439 (5.7) 29 (6.5) 410 (5.6)
 Missing 15 (0.2) 0 (0) 15 (0.2)
Household income 0.290
 Quartile 1 1,807 (23.3) 119 (26.7) 1,688 (23.1)
 Quartile 2 1,855 (23.9) 102 (22.9) 1,753 (24.0)
 Quartile 3 1,865 (24.1) 100 (22.4) 1,765 (24.2)
 Quartile 4 2,032 (26.2) 113 (25.3) 1,919 (26.3)
 Missing 190 (2.5) 12 (2.7) 178 (2.4)
Smoking 2,049 (26.4) 123 (27.6) 1,926 (26.4) 0.528
Obesity status 801 (10.3) 75 (16.8) 726 (9.9) <0.001*
Surgical type 0.797
 Open 2,142 (27.6) 129 (28.9) 2,013 (27.6)
 Laparoscopic 581 (7.5) 33 (7.4) 548 (7.5)
 Other 5,026 (64.9) 284 (63.7) 4,742 (64.9)
Weekend admission 205 (2.6) 30 (6.7) 175 (2.4) <0.001*
Emergent admission 1,057 (13.6) 166 (37.2) 891 (12.2) <0.001*
 Missing 14 (0.2) 0 (0) 14 (0.2)
Hospital bed size <0.001*
 Small 753 (9.7) 50 (11.2) 703 (9.6)
 Medium 1,325 (17.1) 111 (24.9) 1,214 (16.6)
 Large 5,626 (72.6) 284 (63.7) 5,342 (73.2)
 Missing 45 (0.6) 1 (0.2) 44 (0.6)
Hospital location/teaching status <0.001*
 Rural 207 (2.7) 21 (4.7) 186 (2.5)
 Urban nonteaching 1,115 (14.4) 117 (26.2) 998 (13.7)
 Urban teaching 6,382 (82.4) 307 (68.8) 6,075 (83.2)
 Missing 45 (0.6) 1 (0.2) 44 (0.6)
In-hospital mortality 120 (1.5) 7 (1.6) 113 (1.5) 0.994
Prolonged LOSa,b 1,714 (22.5) 187 (42.6) 1,527 (21.2) <0.001*
Unfavorable dischargea 516 (6.8) 61 (13.9) 455 (6.3) <0.001*
Postoperative complication
 Stroke 43 (0.6) 1 (0.2) 42 (0.6) 0.264
 Biliary leaks 266 (3.4) 21 (4.7) 245 (3.4) 0.090
 Bleeding 65 (0.8) 15 (3.4) 50 (0.7) <0.001*
 Sepsis 228 (2.9) 20 (4.5) 208 (2.8) 0.029*
 System infection 38 (0.5) 2 (0.5) 36 (0.5) 0.918
 Pneumonia 229 (2.9) 29 (6.5) 200 (2.7) <0.001*
 Respiratory failure/mechanical ventilation 603 (7.8) 41 (9.2) 562 (7.7) 0.206
 Fever 199 (2.6) 16 (3.6) 183 (2.5) 0.171
 Nausea 250 (3.2) 10 (2.2) 240 (3.3) 0.159
 Abdominal pain 43 (0.6) 5 (1.1) 38 (0.5) 0.091
 Acute liver failure 59 (0.8) 3 (0.7) 56 (0.8) 0.813
 Acute kidney injury 473 (6.1) 43 (9.7) 430 (5.9) <0.001*
 Urinary tract infection 151 (2.0) 12 (2.7) 139 (1.9) 0.176

Values are presented as number (%) or mean±standard error. Percentages may not total 100 due to rounding.

LOS, length of hospital stay.

a7,629 Patients who died in the hospital were excluded (439 with iron-deficiency anemia and 7,190 without).

bLOS >75th percentile (9 days).

*P<0.05.

Table 2.
Associations between iron-deficiency anemia (with vs. without) and in-hospital outcomes
Outcome aOR (95% CI) P-value
In-hospital mortalitya 1.00 (0.49–2.04) 0.993
Prolonged LOSb,c,d 2.76 (2.30–3.30) <0.001*
Unfavorable dischargeb,e 2.42 (1.83–3.19) <0.001*
Complication
 Bleedingf 5.05 (2.92–8.74) <0.001*
 Sepsisg 1.60 (1.04–2.46) 0.032*
 Pneumoniah 2.54 (1.72–3.74) <0.001*
 Acute kidney injuryi 1.71 (1.24–2.35) 0.001*

aOR, adjusted odds ratio; CI, confidence interval; LOS, length of hospital stay.

aAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, smoking, weekend admission, emergent admission, and hospital location/teaching status.

bPatients who died in the hospital were excluded.

cLOS >75th percentile (9 days).

dAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, weekend admission, emergent admission, and hospital location/teaching status.

eAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), sex, insurance status, weekend admission, emergent admission, hospital bed size, and hospital location/teaching status.

fAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including smoking, emergent admission, hospital bed size, and hospital location/teaching status.

gAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), sex, insurance status, smoking, weekend admission, emergent admission, and hospital location/teaching status.

hAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, and obesity status.

iAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), sex, insurance status, household income, obesity status, weekend admission, emergent admission, and hospital location/teaching status.

*P<0.05.

Table 3.
Associations between iron-deficiency anemia and patient outcomes stratified by age, sex, and obesity status
Variable Prolonged LOSa,b,c
 Unfavorable dischargeb,d
 Bleedinge
 Pneumoniaf
aOR (95% CI) P-value aOR (95% CI) P-value aOR (95% CI) P-value aOR (95% CI) P-value
Age (yr)
 <60 1.84 (1.38–2.45) <0.001* 4.80 (2.52–9.14) <0.001* 3.43 (1.31–8.96) 0.012* 2.34 (1.24–4.43) 0.009*
 ≥60 1.97 (1.55–2.51) <0.001* 1.12 (0.80–1.58) 0.513 3.46 (1.75–6.85) <0.001* 1.74 (1.06–2.86) 0.030*
Sex
 Male 2.02 (1.56–2.62) <0.001* 1.69 (1.09–2.62) 0.020* 3.97 (1.60–9.88) 0.003* 1.75 (1.05–2.92) 0.031*
 Female 1.79 (1.37–2.33) <0.001* 1.26 (0.80–1.98) 0.326 3.12 (1.57–6.19) 0.001* 2.24 (1.25–3.99) 0.006*
Obesity
 No 1.85 (1.51–2.27) <0.001* 1.24 (0.86–1.77) 0.253 3.61 (1.99–6.54) <0.001* 1.90 (1.25–2.90) 0.003*
 Yes 2.29 (1.55–3.37) <0.001* 2.81 (1.41–5.59) 0.003* 2.92 (0.94–9.08) 0.064 2.27 (0.93–5.54) 0.072

LOS, length of hospital stay; aOR, adjusted odds ratio; CI, confidence interval.

aAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type and the stratified variable), including age (continuous), insurance status, weekend admission, emergent admission, and hospital location/teaching status.

bPatients who died in the hospital were excluded.

cLOS >75th percentile (9 days).

dAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type and the stratified variable), including age (continuous), sex, insurance status, weekend admission, emergent admission, hospital bed size, and hospital location/teaching status.

eAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including smoking, emergent admission, hospital bed size, and hospital location/teaching status.

fAdjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, and obesity status.

*P<0.05.

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        Impact of iron-deficiency anemia on short-term outcomes after resection of colorectal cancer liver metastasis: a US National (Nationwide) Inpatient Sample (NIS) analysis
        Ann Coloproctol. 2025;41(2):119-126.   Published online April 24, 2025
        DOI: https://doi.org/10.3393/ac.2024.00591.0084
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      Impact of iron-deficiency anemia on short-term outcomes after resection of colorectal cancer liver metastasis: a US National (Nationwide) Inpatient Sample (NIS) analysis
      Image
      Fig. 1. Flowchart of study population selection. HCUP, Healthcare Cost and Utilization Project; NIS, National (Nationwide) Inpatient Sample. aThis sample represents 37,923 hospitalized patients in the entire United States after weighting.

      Fig. 1.

      Impact of iron-deficiency anemia on short-term outcomes after resection of colorectal cancer liver metastasis: a US National (Nationwide) Inpatient Sample (NIS) analysis
      Characteristic Total (n=7,749) Iron-deficiency anemia
      		 P-value
      Yes (n=446) No (n=7,303)
      Age (yr) 59.6±0.2 62.1±0.5 59.5±0.2 <0.001*
       20–29 77 (1.0) 1 (0.2) 76 (1.0) <0.001*
       30–39 356 (4.6) 21 (4.7) 335 (4.6)
       40–49 1,151 (14.9) 56 (12.6) 1,095 (15.0)
       50–59 2,293 (29.6) 111 (24.9) 2,182 (29.9)
       60–69 2,071 (26.7) 122 (27.4) 1,949 (26.7)
       70–79 1,394 (18.0) 93 (20.9) 1,301 (17.8)
       ≥80 407 (5.3) 42 (9.4) 365 (5.0)
      Sex <0.001*
       Male 4,360 (56.3) 212 (47.5) 4,148 (56.8)
       Female 3,389 (43.7) 234 (52.5) 3,155 (43.2)
      Insurance status 0.001*
       Medicare/Medicaid 3,415 (44.1) 231 (51.8) 3,184 (43.6)
       Private including health maintenance organization 3,880 (50.1) 186 (41.7) 3,694 (50.6)
       Self-pay, no-charge, or other 439 (5.7) 29 (6.5) 410 (5.6)
       Missing 15 (0.2) 0 (0) 15 (0.2)
      Household income 0.290
       Quartile 1 1,807 (23.3) 119 (26.7) 1,688 (23.1)
       Quartile 2 1,855 (23.9) 102 (22.9) 1,753 (24.0)
       Quartile 3 1,865 (24.1) 100 (22.4) 1,765 (24.2)
       Quartile 4 2,032 (26.2) 113 (25.3) 1,919 (26.3)
       Missing 190 (2.5) 12 (2.7) 178 (2.4)
      Smoking 2,049 (26.4) 123 (27.6) 1,926 (26.4) 0.528
      Obesity status 801 (10.3) 75 (16.8) 726 (9.9) <0.001*
      Surgical type 0.797
       Open 2,142 (27.6) 129 (28.9) 2,013 (27.6)
       Laparoscopic 581 (7.5) 33 (7.4) 548 (7.5)
       Other 5,026 (64.9) 284 (63.7) 4,742 (64.9)
      Weekend admission 205 (2.6) 30 (6.7) 175 (2.4) <0.001*
      Emergent admission 1,057 (13.6) 166 (37.2) 891 (12.2) <0.001*
       Missing 14 (0.2) 0 (0) 14 (0.2)
      Hospital bed size <0.001*
       Small 753 (9.7) 50 (11.2) 703 (9.6)
       Medium 1,325 (17.1) 111 (24.9) 1,214 (16.6)
       Large 5,626 (72.6) 284 (63.7) 5,342 (73.2)
       Missing 45 (0.6) 1 (0.2) 44 (0.6)
      Hospital location/teaching status <0.001*
       Rural 207 (2.7) 21 (4.7) 186 (2.5)
       Urban nonteaching 1,115 (14.4) 117 (26.2) 998 (13.7)
       Urban teaching 6,382 (82.4) 307 (68.8) 6,075 (83.2)
       Missing 45 (0.6) 1 (0.2) 44 (0.6)
      In-hospital mortality 120 (1.5) 7 (1.6) 113 (1.5) 0.994
      Prolonged LOSa,b 1,714 (22.5) 187 (42.6) 1,527 (21.2) <0.001*
      Unfavorable dischargea 516 (6.8) 61 (13.9) 455 (6.3) <0.001*
      Postoperative complication
       Stroke 43 (0.6) 1 (0.2) 42 (0.6) 0.264
       Biliary leaks 266 (3.4) 21 (4.7) 245 (3.4) 0.090
       Bleeding 65 (0.8) 15 (3.4) 50 (0.7) <0.001*
       Sepsis 228 (2.9) 20 (4.5) 208 (2.8) 0.029*
       System infection 38 (0.5) 2 (0.5) 36 (0.5) 0.918
       Pneumonia 229 (2.9) 29 (6.5) 200 (2.7) <0.001*
       Respiratory failure/mechanical ventilation 603 (7.8) 41 (9.2) 562 (7.7) 0.206
       Fever 199 (2.6) 16 (3.6) 183 (2.5) 0.171
       Nausea 250 (3.2) 10 (2.2) 240 (3.3) 0.159
       Abdominal pain 43 (0.6) 5 (1.1) 38 (0.5) 0.091
       Acute liver failure 59 (0.8) 3 (0.7) 56 (0.8) 0.813
       Acute kidney injury 473 (6.1) 43 (9.7) 430 (5.9) <0.001*
       Urinary tract infection 151 (2.0) 12 (2.7) 139 (1.9) 0.176
      Outcome aOR (95% CI) P-value
      In-hospital mortalitya 1.00 (0.49–2.04) 0.993
      Prolonged LOSb,c,d 2.76 (2.30–3.30) <0.001*
      Unfavorable dischargeb,e 2.42 (1.83–3.19) <0.001*
      Complication
       Bleedingf 5.05 (2.92–8.74) <0.001*
       Sepsisg 1.60 (1.04–2.46) 0.032*
       Pneumoniah 2.54 (1.72–3.74) <0.001*
       Acute kidney injuryi 1.71 (1.24–2.35) 0.001*
      Variable Prolonged LOSa,b,c
      		 Unfavorable dischargeb,d
      		 Bleedinge
      		 Pneumoniaf
      aOR (95% CI) P-value aOR (95% CI) P-value aOR (95% CI) P-value aOR (95% CI) P-value
      Age (yr)
       <60 1.84 (1.38–2.45) <0.001* 4.80 (2.52–9.14) <0.001* 3.43 (1.31–8.96) 0.012* 2.34 (1.24–4.43) 0.009*
       ≥60 1.97 (1.55–2.51) <0.001* 1.12 (0.80–1.58) 0.513 3.46 (1.75–6.85) <0.001* 1.74 (1.06–2.86) 0.030*
      Sex
       Male 2.02 (1.56–2.62) <0.001* 1.69 (1.09–2.62) 0.020* 3.97 (1.60–9.88) 0.003* 1.75 (1.05–2.92) 0.031*
       Female 1.79 (1.37–2.33) <0.001* 1.26 (0.80–1.98) 0.326 3.12 (1.57–6.19) 0.001* 2.24 (1.25–3.99) 0.006*
      Obesity
       No 1.85 (1.51–2.27) <0.001* 1.24 (0.86–1.77) 0.253 3.61 (1.99–6.54) <0.001* 1.90 (1.25–2.90) 0.003*
       Yes 2.29 (1.55–3.37) <0.001* 2.81 (1.41–5.59) 0.003* 2.92 (0.94–9.08) 0.064 2.27 (0.93–5.54) 0.072
      Table 1. Patient demographic characteristics and in-hospital outcomes

      Values are presented as number (%) or mean±standard error. Percentages may not total 100 due to rounding.

      LOS, length of hospital stay.

      7,629 Patients who died in the hospital were excluded (439 with iron-deficiency anemia and 7,190 without).

      LOS >75th percentile (9 days).

      P<0.05.

      Table 2. Associations between iron-deficiency anemia (with vs. without) and in-hospital outcomes

      aOR, adjusted odds ratio; CI, confidence interval; LOS, length of hospital stay.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, smoking, weekend admission, emergent admission, and hospital location/teaching status.

      Patients who died in the hospital were excluded.

      LOS >75th percentile (9 days).

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, weekend admission, emergent admission, and hospital location/teaching status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), sex, insurance status, weekend admission, emergent admission, hospital bed size, and hospital location/teaching status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including smoking, emergent admission, hospital bed size, and hospital location/teaching status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), sex, insurance status, smoking, weekend admission, emergent admission, and hospital location/teaching status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, and obesity status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), sex, insurance status, household income, obesity status, weekend admission, emergent admission, and hospital location/teaching status.

      P<0.05.

      Table 3. Associations between iron-deficiency anemia and patient outcomes stratified by age, sex, and obesity status

      LOS, length of hospital stay; aOR, adjusted odds ratio; CI, confidence interval.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type and the stratified variable), including age (continuous), insurance status, weekend admission, emergent admission, and hospital location/teaching status.

      Patients who died in the hospital were excluded.

      LOS >75th percentile (9 days).

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type and the stratified variable), including age (continuous), sex, insurance status, weekend admission, emergent admission, hospital bed size, and hospital location/teaching status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including smoking, emergent admission, hospital bed size, and hospital location/teaching status.

      Adjusted for related variables with a P-value of <0.05 (univariate analysis, except for surgical type), including age (continuous), insurance status, and obesity status.

      P<0.05.

      Table 1.

      Table 2.

      Table 3.

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