Abstract
To evaluate the association between red blood cell (RBC) indices (mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], MCH concentration [MCHC], red cell distribution width [RDW], hemoglobin [Hb], hematocrit [Hct], and neutrophil-to-lymphocyte ratio [NLR]) and the severity of endometriosis.
Data were obtained from the medical records of 200 patients with endometriosis (stage I/II and stage III/IV groups), and 100 patients with benign ovarian tumors (control group), treated between September 2011 and April 2021.
The mean Hb and Hct were significantly lower in the stage III/IV group compared to those in the control and stage I/II group (P = .015 and P = .004, respectively). The mean MCV, MCH, and Hb at postoperative day (POD)#1 were significantly lower in the stage III/IV group compared to those in the control and stage I/II group (P = .007, P = .032, and P < .0001, respectively). In addition, NLR at POD#1 was significantly higher in stage III/IV group compared to that in the control and stage I/II group. Multivariate analysis revealed that younger age (≤38 years old), lower preoperative MCV (≤88.5 fL), lower POD#1 Hb (<11.6g/dL), and higher POD#1 NLR (>2.5) were independent risk factors of stage III/IV endometriosis.
Lower levels of RBC indices, including preoperative MCV and postoperative Hb, and higher postoperative NLR were significantly associated with the severity of endometriosis, which is potentially derived from a dysregulation in iron metabolism and inflammation.
Keywords: endometriosis, mean corpuscular hemoglobin, mean corpuscular volume, RBC indices, red blood cell, red cell distribution width
1. Introduction
Endometriosis is defined as the presence of endometrial tissue outside the uterine cavity. The estimated prevalence of endometriosis is 10 to 15% in the general population, and up to 70% in women with chronic pelvic pain.[1,2] Patients with endometriosis often experience dysmenorrhea and infertility, resulting in a severely limited quality of life.[2] Despite a large research effort, the etiology and pathophysiology of the disease have not been fully elucidated.[2]
However, it has recently been suggested that endometriosis has a connection with the complete blood cell count.[3–5] Endometriosis is a chronic inflammatory disease, therefore, various inflammatory markers, including lymphocytes, interleukin, and neutrophil-to-lymphocyte ratio (NLR) are elevated in severe endometriosis.[6–8]
Specifically, the NLR has been proposed as a simple and feasible diagnostic or prognostic indicator for various diseases.[3,6,9]
Furthermore, other evidence suggests that an increase in reactive oxygen species (ROS) formation induced by a high iron concentration is an early event in the development of endometriosis.[10]
In addition, several recent studies suggest that more severe endometriosis is associated with a lower hemoconcentration, along with dysregulation of red blood cells (RBC) or iron metabolism.[11,12]
In this study, we aimed to evaluate relationship among the RBC indices (mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], MCH concentration [MCHC], red cell distribution width [RDW], hemoglobin [Hb], hematocrit blood test [Hct]), NLR, and endometriosis.
2. Materials and Methods
Retrospective data was collected from chart review of premenopausal women who underwent laparoscopic surgery for the treatment of benign ovarian tumor at the Department of Obstetrics and Gynecology, Kangnam Sacred Heart Hospital, between September 2011 and April 2021. The study received approval from the institutional review board (IRB no. 2017-02-13). Women who were pathologically confirmed or clinically suspected of pregnancy, leiomyoma, adenomyosis, pelvic inflammatory disease, tuberculosis, hematemesis, endocrine disease, abnormal liver function, heart disease, diabetes, kidney disease, cancer, or an immune system disease were excluded. In addition, women who underwent combined surgery, such as laparoscopic myomectomy and laparoscopic adenomyomectomy were excluded.
Total 300 women were included in this study, of which 200 were pathologically confirmed with endometriosis (study group) and other 100 were pathologically confirmed with other benign adnexal diseases (control group), such as teratoma, serous cystadenoma, and mucinous cystadenoma. Among the 200 patients with endometriosis, 100 women had stage I to II endometriosis (stage I to II group) and 100 women had stage III to IV endometriosis (stage III to IV group). All patients underwent routine preoperative laboratory studies, including a complete blood cell count performed within one month before the surgery. RBC indices and NLR were calculated as follows:
Red cell distribution width [RDW]: (Standard deviation of MCV/MCV) × 100.
Mean corpuscular volume [MCV]: Hct (%) × 10/RBC count (million/μL).
Mean corpuscular hemoglobin [MCH]: Hb (g/dL) × 10/RBC count (million/μL).
Mean corpuscular hemoglobin concentration [MCHC]: Hb (g/dL) × 100/Hct (%).
Hemoblogin [Hb]: MCV × RBC/29.8.
Hematocrit [Hct]: (RBC × MCV)/10.
Neutrophil to lymphocyte ratio [NLR]: neutrophil count/lymphocyte count.
Symptoms including dysmenorrhea, heavy menstrual bleeding, and dyspareunia before surgery were recorded; however, the menstrual cycle of each patient was not considered. The endometriosis score was determined using the revised American Society for Reproductive Medicine guidelines.[13]
Statistical analyses were performed using SPSS version 26.0 (SPSS Inc., Chicago, IL) and Medcalc software (version 15.2.2, Portland, USA). P values <.05 were considered statistically significant. Group differences were evaluated using one-way analysis of variance (ANOVAs), with post hoc comparisons assessed using Duncan Multiple Range test. Multivariate analysis was performed using binary logistic regression. The hazard ratio (HR) and 95% confidence intervals (CI) were calculated. The accuracy of RBC indices and NLR in discrimination of severe endometriosis (stage III–IV) from mild endometriois using the receiver operating characteristics (ROC) curve analysis.
3. Results
The basic patient characteristics are summarized in Table 1, and the symptoms are summarized in Table 2. There were no significant group differences in the mean body weight or body mass index (BMI). Many of the women with endometriosis suffered from dysmenorrhea and heavy menstrual bleeding. Table 3 provides the mean values for RBC, Hb, Hct, MCV, MCH, MCHC, RDW, and postoperative day 1 Hb. Significant group differences were observed for Hb, Hct, MCV, MCH, and Hb at postoperative day (POD)#1 (P = .015, .004, .007, .032, <.0001, respectively). These RBC indices were significantly lower in the stage III to IV group compared to those in the control and stage I to II groups. However, there were no significant group differences in RBC count, MCHC, or RDW.
Table 1.
Group differences in basic patients’ characteristics.
| Characteristics | Control (N = 100) | Stage I–II (N = 100) | Stage III–IV (N = 100) | P value |
|---|---|---|---|---|
| Age(yr) | 41.830 (39.475–44.184) | 32.500 (30.915–34.084) | 30.990 (29.613–32.366) | <.0001** |
| Height(cm) | 160.159 (159.143–161.175) | 160.173 (159.075–161.270) | 161.980 (160.888–163.071) | .024* |
| Body weight(kg) | 56.732 (55.189–58.274) | 55.308 (53.564–57.052) | 55.708 (53.822–57.594) | .493 |
| BMI(kg/m2) | 22.138 (21.538–22.739) | 21.521 (20.942–22.099) | 21.232 (20.548–21.917) | .115 |
| Hospital stay(days) | 5.060 (4.896–5.224) | 4.500 (4.245–4.754) | 5.560 (5.113–6.006) | <.0001** |
Note: Data are presented as mean (95% confidence interval), P values obtained by One-way analysis of variance.
BMI = body mass index.
P < .05.
P < .0001.
Table 2.
Patients’ symptoms.
| Control (N = 100) | Stage I–II (N = 100) | Stage III–IV (N = 100) | Total (N = 300) | |
|---|---|---|---|---|
| None | 74 | 20 | 19 | 113 |
| Dysmenorrhea | 6 | 64 | 61 | 131 |
| Heavy menstrual bleeding | 0 | 26 | 22 | 48 |
| Dyspareunia | 1 | 0 | 0 | 1 |
| Others* | 19 | 51 | 43 | 113 |
Data are presented as number.
Symptoms includes infertility, lower abdominal pain, and back pain.
Table 3.
RBC indices, neutrophil-to-lymphocyte ratio (NLR), and platelet count in each group.
| Control (N = 100) | Stage I–II (N = 100) | Stage III–IV (N = 100) | P value | |
|---|---|---|---|---|
| Preoperative RBC indices | ||||
| RBCs (×106/uL) | 4.302 (4.242–4.362) | 4.259 (4.197–4.322) | 4.264 (4.204–4.323) | .560 |
| Hb (g/dL) | 12.888 (12.668–13.107) | 12.735 (12.551–12.918) | 12.471 (12.267–12.674) | .015* |
| Hct (%) | 38.101 (37.553–38.678) | 37.536 (36.998–38.073) | 36.806 (36.266–37.345) | .004* |
| MCV (fL) | 88.646 (87.521–89.770) | 88.243 (87.326–89.159) | 86.514 (85.581–87.447) | .007* |
| MCH (pg) | 30.039 (29.557–30.520) | 29.950 (29.589–30.310) | 29.312 (28.899–29.725) | .032* |
| MCHC (%) | 33.848 (33.626–34.069) | 33.940 (33.734–34.145) | 33.860 (33.631–34.088) | .814 |
| RDW (%) | 12.786 (12.548–13.023) | 12.698 (12.468–12.928) | 12.767 (12.559–12.974) | .850 |
| POD#1 Hb (g/dL) | 11.778 (11.556–11.999) | 11.723 (11.519–11.926) | 11.110 (10.903–11.316) | <.0001** |
| Preoperative NLR | 2.025 (1.768–2.283) | 2.841 (1.883–3.798) | 2.539 (1.928–3.150) | .229 |
| POD#1 NLR | 3.106 (2.730–3.481) | 3.150 (2.702–3.597) | 4.480 (3.833–5.126) | <.0001** |
| POD#3 NLR | 2.645 (1.785–3.505) | 2.334 (1.996–2.671) | 2.519 (2.207–2.831) | .738 |
| Platelet (×103/uL) | 264.18 (252.93–275.43) | 258.03 (246.33–269.73) | 256.93 (245.50–268.42) | .635 |
Note: Data are presented as mean (95% confidence interval), P values obtained by One-way analysis of variance.
Hb = hemoglobin, Hct = hematocrit blood test, MCV = mean corpuscular volume, MCH = mean corpuscular hemoglobin, MCHC = mean corpuscular hemoglobin concentration, NLR = neutrophil-to-lymphocyte ratio, POD = postoperative day, RBC = red blood cell, RDW = red cell distribution width.
P < .05.
P < .0001.
Mean NLR and platelet counts are also shown in Table 3. Significant group differences were observed in the mean NLR at POD#1 (P < .0001), with higher values in the stage III to IV group compared to those in the control and stage I to II groups. There were no significant group differences in the preoperative NLR, NLR at POD#3, or platelet count.
Multiple logistic regression analysis revealed that younger age (≤38 years old), lower preoperative MCV (≤88.5 fL), lower POD#1 Hb (<11.6g/dL), and higher POD#1 NLR (>2.5) were independent risk factors of stage III/IV endometriosis (Table 4).
Table 4.
Risk factors of severe endometriosis.
| Risk factors | HR (95% CI) | P value |
|---|---|---|
| Age (≤38 yrs old) | 3.936 (1.961–7.898) | <.0001** |
| Preoperative Hb (≤13.0 g/dL) | 0.744 (0.310–1.784) | .507 |
| Preoperative Hct (≤37.9%) | 2.028 (0.892–4.611) | .091 |
| Preoperative MCV (≤88.5 fL) | 2.339 (1.131–4.837) | .022* |
| Preoperative MCH (≤29.5 pg) | 0.830 (0.395–1.744) | .622 |
| POD#1 Hb (<11.6g/dL) | 2.331 (1.211–4.484) | .011* |
| POD#1 NLR (>2.5) | 3.065 (1.725–5.447) | <.0001** |
Hb = hemoglobin, Hct = hematocrit blood test, MCV = mean corpuscular volume, MCH = mean corpuscular hemoglobin, NLR = neutrophil-to-lymphocyte ratio, POD = postoperative day.
P < .05.
P < .0001.
4. Discussion
Endometriosis is related to local and systemic inflammatory processes. The peritoneal microenvironment in women with endometriosis includes an abundance of inflammatory cytokines, chemokines, and prostaglandins. Inflammation is also present in the ectopic endometrium of women with endometriosis.[14] Numerous studies have demonstrated that diverse inflammatory markers are found in the serum and peritoneal fluid of patients with endometriosis. A study evaluating diagnostic value of NLR in endometriosis revealed that NLR shows a lower sensitivity of 57.9% and specificity of 65.2% with a cutoff value at 1.82. Furthermore, the combination of NLR and CA125 has the highest AUC of 0.949 with a sensitivity of 86.8% and specificity of 92.0% at the cutoff value of 44.40.[5]
According to Sampson’s theory, retrograde menstruation is considered as an essential process in the pathogenesis of peritoneal endometriosis.[15] Retrograde menstruation transports menstrual endometrial tissue and RBCs through the fallopian tubes into the peritoneal cavity. In fact, RBCs are present in the peritoneal fluid of most women. A review article reported that 21 studies have demonstrated the presence of iron overload in the different components of the peritoneal cavity (peritoneal fluid, ectopic endometrial tissue, the peritoneum adjacent to lesions, and macrophages).[16] In addition, a study suggested that iron overload by retrograde menstruation induces oxidative stress, which may permit ectopic survival of endometrial cells and lesion vascularization in the peritoneal cavity.[17] Only a few studies have shown that RBC indices have a negative correlation with endometriosis. Kim et al reported that more severe endometriosis is associated with a lower hemoconcentration.[3]
In our study, the mean values of preoperative and postoperative day 1 Hb, Hct, MCV, and MCH were found to be significantly negatively correlated with the existence of endometriosis as well as the endometriosis stage. Thus, these RBC indices appear to be related to endometriosis severity. We suggest that these findings result from a dysregulation in iron metabolism. In humans, the body iron content is ~45 mg Fe/kg body weight, with typically higher values in men than in women. Circulating RBCs contain most of this iron, which is bound to the oxygen transport protein, Hb (~30 mg Fe/kg).[18] Increased concentrations of erythrocytes have been reported in the peritoneal cavity of women with endometriosis.[1] In the case of endometriosis, iron overload may originate from the lysis of pelvic erythrocytes.[19] Iron overload in the pelvic cavity can affect numerous mechanisms involved in the development of endometriosis.[20] Thus, the observed negative correlation between endometriosis severity and specific RBC indices may be derived from a dysregulation in iron metabolism.
However, there was no association between other RBC indices (RBC count, MCH, MCHC, and RDW) and the endometriosis stage. Thus, the pathophysiology of endometriosis requires further evaluation through large randomized controlled trials.
As mentioned above, a number of studies have suggested that severe endometriosis is correlated with NLR elevation.[21–23] A retrospective study including 662 women who had undergone laparoscopic surgery for the treatment of endometriosis revealed that lower NLR was significantly associated with infertility.[21] Also, NLR was significantly higher in patients with endometriotic cysts of >5 cm diameter or oviduct adhesions (P = .008, P = .048, respectively).[21] The authors suggested that NLR may be used as a simple and easily obtained predictive marker for endometriosis with infertility.[21] On the contrary, in our study, only the mean NLR at postoperative day 1 was found to be positively correlated with the existence of endometriosis as well as the endometriosis stage; the preoperative and postoperative day 3 NLRs were not related to endometriosis existence or severity. Therefore, additional large-scale studies are needed to clarify the relationship between NLR and endometriosis.
The strengths of our study include the selection of controls. We included only women who had undergone surgery for an ovarian benign tumor, allowing confirmation that the control subjects did not have endometriosis. The primary limitation of our study concerns its retrospective design. Menstrual cycles can affect the results of complete blood count test. However, we performed blood sampling irrespective of patients’ menstrual cycles, which might be a potential source of bias. In addition, anemia is very common in premenopausal women. Although the exclusion criteria were strictly observed, we could not exclude other hidden causes of anemia.
In conclusion, the present findings demonstrate that lower RBC indices, such as preoperative MCV and POD#1 Hb, and higher POD#1 NLR were significantly associated with stage III/IV endometriosis. We consider that lower RBC indices might be derived from dysregulation of iron metabolism. Also, a higher NLR might be stem from inflammation associated with severe endometriosis. However, the pathophysiology of our findings remains unclear and further multicenter prospective studies are needed to evaluate these findings.
Acknowledgements
The authors would like to thank all the gynecologists of Kangnam sacred Hospital for their kind assistance in collecting samples for this study.
Author contributions
Conceptualization: Hye-Yon Cho, Sung-Taek Park, Sung-Ho Park.
Data curation: Hye-Yon Cho, Sung-Taek Park.
Formal analysis: Hye-Yon Cho, Sung-Ho Park.
Investigation: Hye-Yon Cho, Sung-Taek Park, Sung-Ho Park.
Methodology: Hye-Yon Cho, Sung-Taek Park, Sung-Ho Park.
Resources: Sung-Ho Park.
Supervision: Sung-Ho Park.
Writing – original draft: Hye-Yon Cho.
Writing – review & editing: Hye-Yon Cho.
Abbreviations:
- Hb =
- hemoglobin
- Hct =
- hematocrit
- MCH =
- mean corpuscular hemoglobin
- MCHC =
- MCH concentration
- MCV =
- mean corpuscular volume
- NLR =
- neutrophil-to-lymphocyte ratio
- POD =
- postoperative
- RBC =
- red blood cell
- RDW =
- red cell distribution width
- ROS =
- reactive oxygen species
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
The authors have no funding and conflicts of interest to disclose.
How to cite this article: Cho HY, Park ST, Park SH. Red blood cell indices as an effective marker for the existence and severity of endometriosis (STROBE). Medicine 2022;101:42(e31157).
Contributor Information
Hye-Yon Cho, Email: jugilove@gmail.com.
Sung-Taek Park, Email: vth2000@naver.com.
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