Endometriosis: The long wait for a non-invasive test

People with endometriosis today have to wait for 6.7 years on average for a diagnosis.

April 10, 2023 10:30 am | Updated April 16, 2023 12:20 pm IST - Bengaluru

A diagram showing the potential locations of endometriosis.

A diagram showing the potential locations of endometriosis. | Photo Credit: Tsaitgaist/Wikimedia Commons, CC BY-SA 3.0

Endometriosis is a painful chronic disease in which tissue similar to the lining of the uterus, or endometrium, grows outside of it. Despite its prevalence, popular awareness of endometriosis remains low even as its diagnosis is marred by experiences of medical misogyny and gaslighting.

This year, however, there may also be some (cautious) cheer: a U.S. based company named DotLab has announced a blood test to reliably diagnose endometriosis. The significance of this technology is highlighted by the fact that people have to wait for 6.7 years on average for a diagnosis, even as the number of people with endometriosis could be much higher than the estimated 190 million worldwide (about 42 million in India alone), due to the number of cases that go undiagnosed.

Why is endometriosis hard to diagnose?

Doctors often struggle to diagnose endometriosis because of its variety of symptoms, including painful menstruation, urination, sexual intercourse, bowel movements, fatigue, and sometimes infertility. There are also no reliable non-invasive diagnostic tools (ultrasound can’t accurately detect all forms of endometriosis). Laparoscopic surgery is required for a definitive diagnosis.

DotLab has said that its blood test is the first of its kind: a non-invasive method to accurately diagnose endometriosis.

This test relies on detecting microRNA, which are small, non-coding RNA segments that regulate gene expression. Many studies have identified microRNAs that are expressed differently in people with endometriosis. So, on paper at least, researchers can use these unique expression patterns as a sign of the disease. Currently, researchers are exploring the use of microRNA from saliva and blood as diagnostic biomarkers. 

The blood test by DotLab is the product of a study (published in the American Journal of Obstetrics & Gynaecology in March 2020) in which researchers identified blood-based microRNAs that were expressed differently in people with endometriosis, relative to a group of people who didn’t have the disease.

The researchers then created an algorithm combining the expression values of these microRNAs to predict the presence or absence of endometriosis. They validated it with a different group of people and found that it was able to accurately identify those who did have endometriosis.

Is the new test available to use?

Ramanaiah Mamillapalli, a research scientist at the Yale School of Medicine who was involved in the study, cautioned that “this microRNA screen is at testing level only”. Indeed, DotLab is actively recruiting people to participate in ongoing clinical trials expected to be completed by September 2024. The U.S. Food and Drug Administration hasn’t yet approved the test.

The researchers also noted that while the test was able to accurately identify both mild and advanced endometriosis, it wasn’t able to differentiate between the stage and the severity of the disease.

Abhishek Mangeshikar, director of the Indian Centre for Endometriosis, an “educational resource” for physicians and patients, agreed that the test could give a ‘yes’ or ‘no’ answer about whether someone has endometriosis – “but it’s not giving you a status or a stage of the disease … and which organs [could be] involved.”

He also noted the importance of the test’s sensitivity and specificity, found to be 83% and 96%, respectively.

Sensitivity refers to the test’s ability to correctly identify the disease based on microRNA expression levels, i.e. its ability to identify true-positive results. Specificity is a measure of the test’s ability to reliably say that some abnormal microRNA expression is the result of endometriosis, and not some other condition. It’s the test’s ability to avoid false-positive results.

Hugh Taylor, the chief of obstetrics and gynaecology at Yale-New Haven Hospital, said there is a way to improve these numbers: “There are thousands of microRNAs expressed differently in endometriosis, so we can use combinations to get a very specific disease signature.”

Dr. Taylor helped develop the test’s technique that DotLab has since patented.

What do we know about endometriosis?

Endometriosis was first characterised in 1860 but its first biomarkers were found only 150 years later.

“People have been looking for biomarkers of endometriosis for years,” Dr. Taylor said. Most of them were related to inflammation, which is not specific to endometriosis because it’s observed in many diseases. Even when a marker was found, the results were inconsistent.

“Endometriosis is not a life-threatening disease and it comes under reproductive biology, which is not greatly supported by funding agencies,” Dr. Mamillapalli said. “So pharma companies are not focusing enough on this disease.”

Endometriosis research is severely underfunded worldwide. A May 2022 report by the U.S. National Institutes of Health stated that endometriosis research accounted for only 0.05% of the institutes’ total research budget.

There are isolated pockets of well-funded research, however. In 2021, for instance, Rahul Gajbhiye, a clinician-scientist at the Indian Council of Medical Research’s National Institute for Research in Reproductive Health, Mumbai, received a grant of Rs 3.6 crore to study endometriosis.

Better funding is one component of  designing effective and accessible diagnostic tools.

Another is affordability. “If the test is expensive, I may prescribe it only as an additional measure, if a patient’s clinical history is suggestive of endometriosis but they don’t have any positive imaging findings,” Dr. Mangeshikar said. “But if it is cost-sensitive, then this [could] become a routine screening test as part of the diagnostic pathway.”

What are the benefits of a test for endometriosis?

Further, if the test is successful, it could have clinical implications that include reduced time to diagnosis, disease progress, fewer years of discomfort, and lower surgical risk

Ananya Petkar, an independent gynaecologist and former faculty member at Mumbai’s KEM Hospital, noted that doctors prescribe treatment for symptomatic relief even before a formal diagnosis and that most doctors only advise surgery if medical management does not successfully ameliorate symptoms.

“If a blood test tells you the diagnosis, there is no need to do a laparoscopy if [the person] is benefitting from medical management,” Dr. Petkar said. She added that the results of the test sound promising, and if successful, it could reduce the time to diagnosis.

In addition to these clinical implications, understanding which microRNAs are abnormal in endometriosis could also help researchers identify which genes, and thus which pathways, are involved in the disease, which in turn could help unravel its complex biology and offer potential targets for therapy.

Sneha Khedkar is a biologist-turned freelance science journalist based out of Bengaluru.

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