A new saliva test for endometriosis is in trials. What this and other new endo tests mean for you

It can take years for someone to be diagnosed with endometriosis. This can mean ongoing pain, repeated appointments and uncertainty, and delayed treatment. However, two new tests are being trialled in the United Kingdom. One is a saliva test; the other measures electrical activity in the gut. Over the next three years, these non-invasive tests will be used in general practice patients to see if they can help diagnose endometriosis much sooner. The promise of these and other non-invasive tests to speed up diagnosis is compelling. But the evidence is not there yet for their widespread use. Why is endometriosis so difficult to diagnose? Endometriosis is a condition where tissue like the lining of the uterus is found outside the uterus. It commonly causes severe period and pelvic pain, pain during intercourse, bowel and bladder problems, and difficulty becoming pregnant. Diagnosis involves assessing symptoms, a physical examination, imaging and sometimes surgery. Ultrasound and MRI can diagnose endometriosis when performed by a health professional with specific extra training. But a normal scan does not rule out endometriosis. So laparoscopy, surgery using a small camera inserted into the abdomen, may still be considered. Then there are the two non-invasive tests being trialled in the UK but are not available in Australia. What can these offer? Endotest is a saliva test Endotest analyses a saliva sample for specific markers called microRNAs – tiny molecules involved in controlling how genes behave. Specific patterns of these microRNAs can indicate whether endometriosis is likely present. A French study of 971 patients across multiple centres reported the test was highly accurate. But most participants had endometriosis. That’s unlike typical GP patients presenting with symptoms of pelvic pain, only some of whom will have endometriosis. Pelvic pain can have bowel, bladder, muscular and other causes. So we don’t know if the test performs as well in the typical mix of patients you’d expect to see in general practice. EndoSure looks at your gut EndoSure detects endometriosis by measuring electrical signals in the gut via sensor pads on the abdomen. The test takes 45 minutes and can take place in a GP or specialist clinic. A study of 154 women reported 95% sensitivity (the ability to correctly detect endometriosis) and 96% specificity (the ability to correctly rule out people who do not have endometriosis). However, most of the evidence supporting the specificity figure came from controls who did not have surgery to confirm they really did not have endometriosis. Preliminary findings from a later study compared just 25 women with confirmed endometriosis with 25 controls. Most of the women in the control group had abdominal symptoms but were, again, not surgically confirmed as endometriosis-free. The study was also not able to establish whether other conditions could interfere with the test. The researchers noted adenomyosis might produce similar signals. More recent, unpublished findings presented at a scientific meeting found EndoSure detected everyone who had endometriosis. However, its reported specificity was just 5%, compared with around 96% in the earlier study. This means 95% of people without endometriosis still tested positive. If confirmed in larger studies, that would raise serious questions about its usefulness in general practice, where doctors need to distinguish endometriosis from the many other conditions that can cause similar symptoms. How about other tests? Other non-invasive tests for endometriosis are in development, including blood tests. Not all are widely available or have been independently validated. EndomTest is a blood test available in the United States that combines its results with clinical information. But the US Food and Drug Administration has not approved it for widespread use. Published results found high specificity for diagnosing endometriosis. But it had much lower sensitivity, meaning it could miss many people who have endometriosis. Australia’s PromarkerEndo measures proteins in blood. Importantly, testing has involved patients with symptoms but where surgery has found no endometriosis. This is a strong comparison because, when used clinically, the test has to distinguish between patients with similar symptoms who do and don’t actually have the disease. Results have been promising across early-stage disease, although further independent validation is needed. US-developed DotEndo examines microRNAs in blood. Earlier research found a panel of six-microRNAs could distinguish endometriosis from other gynaecological conditions. A large, multi-centre study is evaluating its use in around 750 patients. Impressive numbers need context When we evaluate a diagnostic test, the question is not simply “How accurate is this test?” but “How well does it work in the people who will actually use it?”. Even so, for a test to be useful, it should change what happens next by raising suspicion, prompting investigation, guiding treatment, or providing an explanation sooner. So such tests may help answer “Could this be endometriosis?”. But imaging will still be needed to show where and how extensive the disease is. Doctors will still need to assess adhesions – scar-like tissue that can cause pelvic organs to become stuck together. This mapping guides treatment and, if surgery is considered, its complexity and which specialists may be involved. If such tests help patients access specialist ultrasound earlier, this could be useful. The same care is needed with a negative result. Unless a test reliably rules out endometriosis in the population being tested, a negative result should not be used to dismiss persistent symptoms. Even without endometriosis, pelvic pain still deserves investigation and care.