Healthcare Guide · November 10, 2026

How Is Endometriosis Diagnosed? Five Tests, and What Each One Can and Cannot Show

Endometriosis affects an estimated 10% (190 million) of reproductive-age women, and the average time to diagnosis is 4 to 12 years (WHO). Taipei Veterans General Hospital lists five diagnostic methods: laparoscopy with biopsy, ultrasound, serum CA-125, MRI and pelvic examination. Ultrasound is the fastest non-invasive first step, but a normal scan or a normal CA-125 does not rule the disease out.

Endometriosis affects an estimated 10% of reproductive-age women, about 190 million people, according to the World Health Organization. The same fact sheet puts the average time to diagnosis at between 4 and 12 years. Part of that delay is that no single test settles the question. The Department of Obstetrics and Gynecology at Taipei Veterans General Hospital (TVGH) publishes a patient guide by Dr. Chen Yi-Jen that lists five ways the disease is diagnosed. This article walks through those five, and what each one can and cannot show.

What is endometriosis, and why does diagnosis take so long?

Endometriosis is a chronic disease in which tissue similar to the lining of the uterus grows outside the uterus. The WHO lists its symptoms as severe pain during menstruation, heavy menstrual bleeding, chronic pelvic pain, infertility, and abdominal bloating and nausea. Some women have no symptoms at all.

The WHO notes that the symptoms are variable and broad, so healthcare workers may not easily diagnose it. Painful periods are also easy to dismiss as normal. There is currently no cure, and treatment aims to control symptoms and limit long-term impact, which is why an earlier diagnosis matters.

What are the five ways endometriosis is diagnosed?

The TVGH guide names laparoscopy with biopsy, ultrasound, serum CA-125, MRI and pelvic examination. The table summarises what the guide says about each.

Method	What it can show	Its limit
Laparoscopy with biopsy	Direct view of lesions in the pelvis: granules, small nodules or large cysts, with dark red or black deposits	It is surgery. A negative biopsy does not prove endometriosis is absent
Ultrasound	Large cysts, including ovarian "chocolate cysts" (endometriomas)	Cannot see lesions on the peritoneum
Serum CA-125	Often above 35 IU/mL in women with endometriosis	Not a reliable diagnostic test. Mild disease usually does not raise it
MRI	Suspected spread to the bladder, ureter or bowel	Not a routine test
Pelvic examination	Pelvic pain, a retroverted uterus, tender or nodular uterosacral ligaments	Depends on timing. Deep nodules are easier to feel during a period

Is an ultrasound enough to diagnose endometriosis?

Sometimes. TVGH calls ultrasound the fastest and non-invasive method. It shows large cysts and helps diagnose a chocolate cyst, the ovarian form of the disease.

Its blind spot is the peritoneum, the membrane lining the pelvis. The TVGH guide states plainly that ultrasound cannot see lesions there. The 2022 guideline from the European Society of Human Reproduction and Embryology (ESHRE) says the same thing from the other direction: a negative imaging result does not exclude endometriosis, particularly superficial peritoneal disease.

So a normal ultrasound is not an all-clear. If the symptoms continue, the conversation with a gynecologist should continue too.

Does a high CA-125 mean endometriosis?

No, and a normal CA-125 does not rule it out either. CA-125 is a protein measured in a blood sample. The TVGH guide says women with endometriosis usually have a higher level, above 35 IU/mL. The concentrations it lists for stage 1 through stage 4 disease are 19, 40, 77 and 182.

Read those four numbers again: stage 1 sits below the 35 threshold. That is why the guide concludes CA-125 is not a dependable way to diagnose the disease. Mild endometriosis does not raise it.

ESHRE goes further and recommends that clinicians not use biomarkers in blood, endometrial tissue, or menstrual or uterine fluid to diagnose endometriosis. CA-125 also rises for unrelated reasons, which we cover in our guide to tumor marker tests.

When is an MRI used for endometriosis?

Rarely as a first test. TVGH reserves MRI for cases where the doctor suspects the disease has reached the bladder, the ureter or the bowel, and says it is not a routine examination. ESHRE lists MRI alongside ultrasound as an imaging option in the diagnostic work-up.

What can a pelvic examination find?

The TVGH guide lists four findings: pelvic pain, a uterus tilted backwards, and tenderness or nodules on the uterosacral ligaments that hold the uterus in place. For deep nodules, it adds that examining during a menstrual period can be more accurate and raises diagnostic accuracy to 94%.

ESHRE is more cautious. It says clinical examination should be considered but that its diagnostic accuracy is low, and that imaging should still be considered when the examination is normal.

Is laparoscopy still the gold standard?

The TVGH guide, last updated in January 2016, calls laparoscopy the gold standard and the most accurate method. A surgeon looks into the pelvis through a small camera and takes a sample of anything suspicious. The guide adds a caveat that still holds: a negative biopsy does not mean endometriosis is absent.

Guidance has moved since then. The 2022 ESHRE guideline challenges laparoscopy and histology as the gold-standard tests. It recommends imaging first, and laparoscopy for patients whose imaging is negative or in whom empirical treatment was unsuccessful or inappropriate. The WHO likewise says a clinical diagnosis may be made on symptoms and imaging such as ultrasound or MRI, and that surgery is not necessarily required before starting treatment.

In practice this means many women can now be diagnosed and treated without an operation. Surgery remains the route when imaging is clear and the symptoms are not.

What should you do if you suspect endometriosis?

Write down the pattern. The WHO says a careful menstrual history covering pain, heaviness of bleeding and associated symptoms can help with diagnosis. Note when the pain starts, how long it lasts and what it stops you doing.
See a gynecologist, not only a general check-up. The work-up starts with a history and, where appropriate, a pelvic examination.
Have a pelvic ultrasound. It is the fastest non-invasive test and can identify a chocolate cyst.
Treat CA-125 as a supporting number. It cannot confirm or exclude the disease on its own.
Ask what happens if the scan is normal. A normal scan does not exclude endometriosis. The next steps are a trial of treatment, MRI, or laparoscopy, and the choice belongs to you and your doctor.

How can New Dawn Health help?

New Dawn Health arranges gynecology consultations with ultrasound at partner clinics and hospitals in Taipei, and MRI when a physician asks for it. We handle the booking and communication in English. We do not diagnose; the gynecologist does.

If painful periods, pelvic pain or difficulty conceiving have gone unexplained, contact New Dawn Health and tell us what you have been experiencing and which tests you have already had. We will reply with the options that fit your situation and your travel dates. If you want to know how an appointment works first, read how to see a gynecologist in Taiwan.

Sources

This article is general education, not medical advice. Diagnosis and treatment of endometriosis belong with a physician who has examined you.