Nitric oxide as a biomarker for patients with endometriosis: a systematic review and meta-analysis

Endometriosis causes pelvic pain, inflammation, and increased oxidative stress levels. To assist in the diagnosis of endometriosis and molecular mechanisms, we propose synthesize the studies that NO levels in different samples using a systematic review and metanalysis. We also evaluate NO levels in different stages of endometriosis.

The protocol was registered with PROSPERO (CRD42023397591). We searched for all articles published up to November 2023 that evaluated NO levels in patients with endometriosis compared to control patients. We used the Newcastle-Ottawa Scale (NOS) to estimate the quality of the articles and the risk of bias. Publication bias was assessed using the Egger test and Begg test.

In this study, 5795 articles were found, after revision 14 studies with 666 control patients and 881 patients with endometriosis were included. NO levels in the combined analysis of all samples from endometriosis patients were increased compared to control patients. Patients with type III/IV endometriosis showed higher levels of NO compared to controls in peritoneal fluid and serum/plasma. The increase in NO levels in patients with type III/IV endometriosis has a high quality of evidence without publication bias.

Here we demonstrate the increase of NO in peritoneal fluid samples from endometriosis patients. Therefore, NO levels may be directly linked to the pathophysiology of endometriosis and can be involved in the severity of endometriosis and inflammatory mechanisms.