Explaining unexplained infertility through non-surgical endometriosis diagnosis

Laparoscopy is the gold standard for diagnosing endometriosis, but other non-surgical tests are showing potential. Here we’ll take a brief look at ReciptivaDx based on the BCL6 protein, the Endotest and DotEndo test based on a miRNA signature, the EMScore which is based on a gene expression signature, and imaging tests like ultrasound and MRI.

Studies have found that about half of women with unexplained infertility have endometriosis (Meuleman et al. 2009, Kanda et al. 2006, Tsuji et al. 2009).

These patients could be experiencing silent endometriosis, where they are lacking symptoms like pain that prevent diagnosis.

Since endometriosis diagnosis requires laparoscopy, a surgical procedure that requires anesthesia, many patients will potentially go years without treatment.

It’s important to develop non-surgical diagnostic tests for endometriosis, so patients can perform these tests first before going on to laparoscopy.

Here we’ll look at a few non-surgical tests for diagnosing endometriosis.

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Table of Contents

BCL-6 and ReceptivaDx to diagnose endometriosis

BCL6 is a protein that is produced in response to inflammation, and is typically seen in patients with endometriosis. BCL6, and another protein called SIRT1, can lead to reduced progesterone signalling and progesterone resistance that’s characteristic of endometriosis (Zhang and Wang 2023).

Evans-Hoeker et al. (2016) performed endometrial biopsies on women with endometriosis, and measured the amount of BCL6 by immunohistochemistry. From this, they generated a H-SCORE to quantify the amount of BCL6. Women with a HSCORE of 1.4 was used as a cutoff for patients with or without endometriosis.

They then used this cutoff to evaluate women with unexplained infertility. They found that 88% tested positive for BCL6 (>1.4), with 93.8% of these patients being positive for endometriosis after laparoscopy.

This test is marketed as ReciptivaDx.

Here’s some details of a study by Nezhat et al. (2020), which wasn’t sponsored by ReciptivaDx:

Patients had unexplained infertility or recurrent pregnancy loss and tested positive with ReceptivaDx (BCL6 negative patients weren’t included).
Only patients who were considering surgery for potential endometriosis were included.
96% of BCL6 positive patients (72 of 75) had type I and IIC endometriomas (by laparoscopy and histology). These were surgically removed.
3 of the patients didn’t have endometriomas by laparoscopy/histology, but had fibrosis and adhesions, which may have led to increased BCL6.
40 patients were followed for pregnancy outcomes within 6 months of surgical removal of endometriomas, resulting in a clinical pregnancy rate of 90.0%.
Limitations: About 10% of patients had both endometriosis and endometritis, and it’s possible that inflammation from endometritis could also trigger a BCL6-positive result. There were also no BCL6 negative patients in this study.

Note that the ReciptivaDX test also tests for a marker called CD138, which can be used to test for endometritis. I don’t know when this marker was added, but was probably after the above study was released.

miRNAs to diagnose endometriosis

Saliva miRNAs and the Endotest

miRNAs are short RNA molecules that work in turning certain genes off. There are thousands of miRNAS and many of our genes are regulated by miRNAs.

Bendifallah et al. (2022) described the potential of miRNAs in diagnosing endometriosis using saliva, in their ENDO-miRNA study. They used AI to identify a unique miRNA signature in endometriosis patients made up of 109 miRNAs that showed high diagnostic potential.

This test is currently being validated in 1,150 patients in a multicenter study, with preliminary results for the first 200 patients published by Bendifallah et al. (2023). The test had a very high AUC of 0.96, showing high sensitivity and specificity in diagnosing endometriosis patients. This trial is registered as NCT05244668.

This test is marketed as the Ziwig Endotest.

Serum miRNAs and the DotEndo test

Moustafa et al. (2020) developed a diagnostic test for endometriosis based on 7 miRNAs from blood serum. This test had a high AUC of 0.94.

Expression levels of these miRNAs were able to detect early (I/II) and advanced (III/IV) endometriosis stages from patients without endometriosis. However, in patients with endometriosis, it couldn’t detect the difference between stages.

This test is marketed as the DotEndo test.

Other tests

Besides miRNAs, another group of small RNAs called piRNAs might help in diagnosing endometriosis. Dabi et al. (2023) used data from the ENDOmiRNA study above, which identified 201 piRNAs. Only a few of them had potential in diagnosing endometriosis, however the AUC values were lower than with the miRNA signature.

Gene expression signatures to diagnose endometriosis

Besides BCL6 and miRNAs, researchers have been searching for other markers associated with endometriosis.

A study by Su et al. (2023) looked at the expression of 9 genes that were added up to give an overall score, called the “endometrial mRNA score” or EMScore.

They found that the EMScore was high in patients with endometriosis and could potentially be used to diagnose the disease by a blood test.

Another endometriosis signature, developed by Chen et al. (2023), is based on the expression of 5 genes (CHPF, CITED2, GPC3, PDK3 and ADH6). Predictions made by EMScore were found to be more accurate than this signature.

While these results are promising, the researchers stress that they need to try this test out in a larger number of patients in multiple IVF centers. This way, they can be more confident that their diagnostic test works in identifying endometriosis.

Imaging tests to diagnose endometriosis

Ultrasound may be able to help diagnose endometriosis. A 2016 Cochrane review found that transvaginal ultrasound could help to determine whether or not laparoscopy was needed, but couldn’t replace this surgery.

The same Cochrane review also looked at magnetic resonance imaging (MRI) in diagnosing endometriosis. They found that MRI might be able to replace laparoscopy for diagnosing endometriomas, but few studies have been done (in 2016). A more recent review by Kido et al. (2022) seems to suggest that MRI can diagnose a wide range of endometriosis types.

It’s important to recognize that both these techniques require substantial skill to perform, so the skill of the operator may determine whether or not diagnosis is possible. This is echoed by a 2019 study that found that the skill of the transvaginal ultrasound operator dictated diagnosis.

Conclusions

Diagnosing endometriosis requires laparoscopy, but promising alternatives that are non-surgical are emerging. This could potentially shorten the time that unexplained infertility patients receive surgical treatment.

ReciptivaDx requires an endometrial biopsy to detect BCL6, while the Endotest and DotEndo detect miRNA in saliva or blood to diagnose endometriosis. Positive results from these tests can help to guide patients and doctors to consider laparoscopy for surgical treatment.

While the DotEndo test could detect earlier and advanced stages of endometriosis, I’m not sure on whether or not the other tests can detect these earlier stages. There are also different forms of endometriosis that these tests may not detect, or different diagnoses (like endometritis) that might give a false positive.

It’s important to recognize that these tests are not 100% but are a starting point to help guide patients to consider laparoscopy. Laparoscopy isn’t 100% either, as lesions can be hidden and the doctor might miss them. In these cases, ultrasound or MRI might help.

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.