Red blood cell indices as an effective marker for the existence and severity of endometriosis (STROBE).

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.