Testing for endometriosis typically involves a combination of symptom evaluation, pelvic exam, imaging, and in many cases, a surgical procedure called laparoscopy to confirm the diagnosis. There is no single quick test that definitively detects endometriosis, which is a major reason the average time from first symptoms to diagnosis ranges from 4 to 12 years, according to the World Health Organization.
Why There’s No Simple Test
Endometriosis happens when tissue similar to the uterine lining grows outside the uterus, on organs like the ovaries, bowel, bladder, and the ligaments supporting the uterus. These growths can look dramatically different from person to person. Some lesions are red and active, others are old and black, and some are white and scarred over. They also range from tiny surface-level spots to deep nodules that burrow into organ walls. This variety makes the condition difficult to capture with any single diagnostic method.
Blood tests, urine tests, and other lab-based biomarkers have been studied extensively, but European guidelines from the ESHRE specifically recommend against using biomarkers in blood, menstrual fluid, or uterine tissue to diagnose endometriosis. They simply aren’t reliable enough. The blood marker CA-125, sometimes used to screen for ovarian cancer, is occasionally elevated in endometriosis, but its accuracy tops out around 79% when no ovarian cysts are involved, and it performs even worse at distinguishing endometriosis from other pelvic conditions.
The Pelvic Exam
A pelvic exam is usually the first hands-on step. Your provider feels for abnormalities by pressing on the abdomen and performing an internal exam. The most telling finding is tender, nodular masses along the ligaments behind the uterus or in the space between the uterus and rectum. A uterus that’s fixed in a tilted-back position and can’t be moved during the exam suggests more extensive disease. Occasionally, a bluish nodule is visible on the vaginal wall where deep endometriosis has infiltrated through.
That said, many people with endometriosis have a completely normal pelvic exam. The most common finding is nonspecific tenderness, which could point to several conditions. Tenderness is most detectable during menstruation, so some providers will schedule the exam during your period. Even when the exam is normal, guidelines recommend moving on to imaging rather than stopping the workup.
Ultrasound
Transvaginal ultrasound, where a small probe is inserted into the vagina for a close-up view of the pelvic organs, is the most common imaging tool. It’s good at detecting ovarian endometriomas (sometimes called “chocolate cysts” because of the dark old blood they contain), but its ability to find deeper disease varies by location.
A large meta-analysis found that transvaginal ultrasound catches bladder endometriosis about 62% of the time, vaginal endometriosis 58% of the time, and endometriosis on the ligaments behind the uterus only about 53% of the time. When it does flag something, though, it’s highly accurate: specificity (the chance it’s correct when it says endometriosis is there) ranges from 93% to 100% depending on location. In practical terms, this means ultrasound is better at confirming disease it does find than at ruling out disease it might miss.
MRI
MRI is typically reserved for cases where deep endometriosis is suspected or where surgery is being planned and the surgeon needs a detailed map of where disease has spread. It’s especially useful for evaluating endometriosis involving the bowel, bladder, and ureters.
On MRI, endometriotic lesions tend to appear as dark, dense nodules with irregular or star-shaped edges, reflecting the scar tissue and muscle overgrowth that surrounds them. Tiny bright spots within those nodules represent trapped endometrial glands. The scan can also reveal adhesions (bands of scar tissue pulling organs out of position), thickened ligaments, and bowel wall involvement. Bladder endometriosis shows up as localized wall thickening, sometimes with bright spots indicating old bleeding inside the tissue.
Like ultrasound, MRI can miss superficial endometriosis (small, flat implants sitting on the surface of the pelvic lining). A normal MRI does not rule out the condition.
Laparoscopy: The Definitive Test
Laparoscopy remains the gold standard for confirming endometriosis. It’s a minimally invasive surgery performed under general anesthesia. A small camera is inserted through an incision near the navel, giving the surgeon a magnified, direct view of the pelvic and abdominal organs. The surgeon inspects the entire area for lesions, which can appear as red, black, or white spots, raised nodules, or clear blisters depending on how long they’ve been there and how active they are.
When suspicious tissue is found, the surgeon takes small biopsies using punch forceps. These tissue samples go to a pathology lab, where a diagnosis is confirmed by the presence of endometrial glands, surrounding supportive tissue called stroma, scar tissue, and specific immune cells that contain iron from old blood. Guidelines recommend histological confirmation because visual identification alone isn’t perfectly reliable. Some lesions that look like endometriosis under the camera turn out to be something else, and some that don’t look typical turn out to be endometriosis on biopsy.
In many cases, the surgeon treats endometriosis during the same procedure by removing or destroying the lesions. If ovarian cysts are found, they’re typically removed at that time as well. Recovery from a diagnostic laparoscopy usually takes a few days to two weeks, depending on how much work was done during the procedure.
When Laparoscopy Is Recommended
Not everyone with suspected endometriosis goes straight to surgery. Current European guidelines lay out a stepped approach: symptom assessment first, then physical exam, then imaging with ultrasound or MRI. If imaging is negative but symptoms are strong, a trial of hormonal treatment (like birth control pills or progestins) is sometimes offered. Laparoscopy is recommended when imaging is negative but symptoms persist, when empirical treatment hasn’t worked, or when the clinical picture requires a definitive answer, such as in infertility cases or when planning complex treatment.
How Endometriosis Is Staged
If endometriosis is confirmed at surgery, it’s classified using a point system developed by the American Society for Reproductive Medicine. The surgeon scores each lesion based on its size, depth, and location, and adds points for adhesions and ovarian involvement. The total determines the stage:
- Stage I (minimal): 1 to 5 points, typically a few small, superficial implants
- Stage II (mild): 6 to 15 points, more implants that are slightly deeper
- Stage III (moderate): 16 to 40 points, often involving ovarian cysts and some adhesions
- Stage IV (severe): over 40 points, with large cysts, dense adhesions, and deep organ involvement
One important thing to know: the stage doesn’t always match the level of pain. Some people with Stage I endometriosis have debilitating symptoms, while some with Stage IV have relatively mild ones. The staging system describes the physical extent of disease, not the severity of what you feel.
Saliva Tests on the Horizon
A saliva-based test that analyzes a panel of 109 small genetic fragments called microRNAs has shown promising results in validation studies. Interim data from a multicenter trial reported 96% sensitivity and 95% specificity, meaning it correctly identified endometriosis in the vast majority of cases and rarely flagged someone who didn’t have it. This kind of non-invasive test could eventually shorten the years-long diagnostic delay that many people experience. It is not yet widely available or approved for routine clinical use, but it represents the closest any non-surgical test has come to matching the accuracy of laparoscopy.