- 01Bloods measure the damage, not the disease
No blood test diagnoses endometriosis; NICE says not to use CA-125 for it. What your bloods show is what endometriosis costs you, such as iron lost to heavy periods (low ferritin, hemoglobin and MCV), and they help rule out look-alikes like infection or thyroid disease.
The main endometriosis symptoms are period pain that disrupts daily life, pelvic pain on most days, deep pain during or after sex, and bowel or bladder pain that flares around your period. They come from tissue similar to the lining of the uterus growing outside it, usually on the ovaries, the pelvic lining and the outside of the bowel and bladder. That tissue responds to estrogen each cycle, inflames the tissue around it and can leave scarring. Doctors diagnose endometriosis from your symptom pattern and imaging. A blood test can show what heavy periods have cost you, such as lost iron, but it cannot confirm the disease.
The symptoms, and why each one happens
NICE, the UK guideline body, lists the symptoms that should make a clinician think of endometriosis: chronic pelvic pain, period pain that affects daily life, deep pain during or after sex, cyclical bowel symptoms such as painful bowel movements, cyclical urinary symptoms such as blood in the urine or pain passing urine, and infertility alongside any of these 2. Each symptom follows from where the lesions (the patches of misplaced tissue) sit and from the inflammation they cause, which is why the timing matters as much as the pain itself.
| Symptom | What it feels like | Why it happens | Tied to the cycle? |
|---|---|---|---|
| Severe period pain | Cramping or stabbing pain that painkillers barely touch, sometimes starting days before bleeding | Lesions bleed and release inflammatory chemicals (prostaglandins) each cycle | Strongly |
| Chronic pelvic pain | A dull or dragging ache on most days for 6 months or more | Ongoing inflammation, scarring and sensitized pelvic nerves | Worse around periods, but present between them |
| Pain during or after sex | Deep pain on penetration that can last hours | Lesions or scarring behind the uterus or on the ligaments that support it | Often worse near a period |
| Bowel symptoms | Painful bowel movements, diarrhea or constipation, bloating ('endo belly') | Lesions on or near the bowel wall, plus inflammation in the pelvis | Flares around periods |
| Bladder symptoms | Pain when peeing, urgency, occasionally blood in the urine | Lesions on or near the bladder | Flares around periods |
| Heavy periods | Flooding, clots, bleeding through protection | Often from adenomyosis (lining tissue inside the uterine muscle), which frequently coexists | Each period |
| Fatigue | Tiredness that sleep does not fix | Chronic pain, poor sleep, inflammation and, in some, iron loss | Often worse around periods |
| Shoulder-tip pain or breathlessness (rare) | Pain at the tip of the shoulder or chest pain during a period. Sudden breathlessness or chest pain needs emergency care, because lesions in the chest can collapse a lung | Lesions on the diaphragm or in the chest | Strongly |
Where does endometriosis pain hurt? Most often low in the pelvis, on one or both sides, and it can spread to the lower back, down the legs and into the rectum, where it shows up as pain when opening your bowels. Pain at the tip of the shoulder is rare and comes from lesions on the diaphragm. Nausea and low mood around periods are common alongside the pain.
Endometriosis symptoms do not track the amount of disease. Some people with a few small lesions have severe pain, and some with large cysts on the ovaries feel almost nothing until they try to conceive 7. Fatigue on its own deserves a wider look; the fatigue guide covers the other common causes, and the bloating guide covers bloating that does not follow your cycle.
Is it endometriosis, or something else?
Several conditions share pelvic pain, bowel trouble or period problems with endometriosis, and two or more can coexist. The most reliable separator is timing: endometriosis pain rises and falls with the menstrual cycle.
| Endometriosis | PCOS | IBS | Adenomyosis | |
|---|---|---|---|---|
| Main symptom | Cyclical pelvic pain, painful sex | Irregular or missed periods, acne, excess hair | Bowel pain relieved by a bowel movement, changing stool habit | Heavy, painful periods and a bulky, tender uterus |
| Timing | Worse before and during periods | Ongoing; cycles are long or absent | Linked to meals and stress more than the cycle | Each period |
| Periods | Usually regular, often painful | Irregular | Unaffected | Regular, heavy |
| What tests show | Scan may show ovarian cysts or deep lesions; often normal | Raised androgens (male-type hormones such as testosterone), many follicles on ultrasound | Normal bloods and scans; tests rule out other causes | Thickened uterine wall on ultrasound or MRI |
| Our guide | This page | PCOS | IBS | Covered in this table |
How do endometriosis and PCOS symptoms differ? PCOS mainly disrupts ovulation, so periods become irregular, while endometriosis mainly causes pain, with periods that usually arrive on time. As our PCOS guide puts it, "No blood test diagnoses PCOS; the labs confirm, exclude and screen." Endometriosis works the same way, but its hallmark is cycle-linked pain rather than irregular ovulation. Pelvic inflammatory disease, fibroids, interstitial cystitis (a painful bladder condition) and ordinary period pain are the other common look-alikes. Irregular periods and PMS have their own guides.
Why it takes so long to diagnose, and how to shorten it
A 2020 report by the UK All-Party Parliamentary Group on Endometriosis found people waited an average of 8 years from first symptoms to a diagnosis 3. Period pain gets treated as normal, bowel symptoms get labeled IBS, and a clear scan gets read as an all-clear. A symptom diary kept over 2 to 3 cycles gives a clinician the cycle-linked pattern that points to endometriosis.
- 1Pain scoreRate pelvic pain 0 to 10 each day, and note where it sits (pelvis, back, legs, rectum).
- 2BleedingMark bleeding days, how many pads or tampons you used, and any clots or flooding.
- 3Bowel and bladderNote pain on opening your bowels, diarrhea, constipation, pain or blood when peeing.
- 4SexRecord pain during or after sex and how long it lasted.
- 5ImpactNote days missed from work or school and which painkillers you took.
How endometriosis is diagnosed now
Laparoscopy (keyhole surgery to look inside the pelvis) used to be the only accepted route to a diagnosis. The 2022 guideline from ESHRE (the European Society of Human Reproduction and Embryology) changed that: it recommends imaging as part of the work-up and supports starting hormonal treatment on a clinical diagnosis without surgical confirmation 4. A normal scan still leaves endometriosis possible, because small surface lesions rarely show on ultrasound or MRI.
Do not exclude the possibility of endometriosis if the abdominal or pelvic examination, ultrasound or MRI are normal.NICE guideline NG73, Endometriosis: diagnosis and management 2
The usual route to an endometriosis diagnosis
Can a blood test show endometriosis?
No blood, urine or saliva test can diagnose endometriosis. ESHRE recommends against using any biomarker in blood, urine, saliva or tissue for diagnosis 4, and NICE says not to use serum CA-125 to diagnose it 2. CA-125 is a protein that rises in endometriosis but also during periods, with fibroids and with pelvic infection.
NICE also notes that a normal CA-125 (below 35 IU/mL) does not rule endometriosis out 2. A raised result, especially alongside an ovarian cyst, is something a specialist interprets in context. The tumor markers guide explains why one raised marker rarely answers a question by itself.
Blood tests are still useful. They show what endometriosis and heavy bleeding are doing to you, and they help rule out the conditions it gets confused with. NICE recommends a full blood count for anyone with heavy periods 6.
| Test | What it can tell you | What it cannot tell you |
|---|---|---|
| Ferritin, hemoglobin, MCV | Whether heavy periods have drained your iron stores or caused anemia; a low MCV means small red cells, typical of iron loss. See how to read your iron studies | Whether the bleeding comes from endometriosis, adenomyosis or fibroids |
| CRP | Inflammation; a high CRP with fever points toward infection such as pelvic inflammatory disease | Whether you have endometriosis (CRP is often normal in it) |
| TSH, TPO antibodies (a sign of autoimmune thyroid disease) | Thyroid causes of fatigue and heavy periods, such as Hashimoto's; see how to read your thyroid panel | Anything about pelvic lesions |
| AMH | Egg reserve, relevant before ovarian surgery or fertility planning | Whether you can conceive naturally this year |
| CA-125 | Context for a specialist, especially with an ovarian cyst | A diagnosis (NICE advises against using it for one) |
Markers to read beside endometriosis
The four stages, and why stage does not equal pain
The revised system from the American Society for Reproductive Medicine (ASRM) grades endometriosis from stage I to IV based on what a surgeon sees at laparoscopy: the number, size and depth of lesions, ovarian cysts and scarring 7.
| Stage | What the surgeon sees |
|---|---|
| I (minimal) | A few small, superficial lesions |
| II (mild) | More lesions, some deeper |
| III (moderate) | Many deep lesions, small ovarian cysts (endometriomas), some scarring |
| IV (severe) | Large endometriomas and dense scarring (adhesions) that can bind organs together |
The endometriosis stage correlates poorly with pain 7. Stage I disease can cause disabling pain, and stage IV can be found by chance during fertility tests. Stage helps a surgeon plan an operation; it does not tell you how much your symptoms should hurt.
What causes it, and who gets it
No single cause explains endometriosis. Retrograde menstruation, where period blood flows backward through the fallopian tubes into the pelvis, happens in most people who menstruate, so it cannot be the whole story. The leading explanations add immune and inflammatory changes that let the tissue survive, dependence on estrogen, and resistance to progesterone's calming effect on the tissue 7.
Inheritance accounts for about half of the risk in twin studies, and a mother or sister with endometriosis raises your own risk 7. Endometriosis is also linked with higher rates of autoimmune conditions such as lupus, rheumatoid arthritis, celiac disease and inflammatory bowel disease 8. Endometriosis is not cancer. It is linked with a higher risk of ovarian cancer overall, about 1.9 times the usual risk in a 2021 meta-analysis, with the rise concentrated in two types, clear-cell (about 3.4 times) and endometrioid (about 2.3 times); the absolute lifetime risk stays low 9.
Treatment options
Endometriosis has no cure. Treatment aims to control pain, protect fertility where that matters, and limit recurrence. The right mix depends on your symptoms, your age and whether you want to become pregnant, so use this table to plan the conversation with your clinician.
| Option | Often used for | Trade-offs |
|---|---|---|
| Anti-inflammatory painkillers (NSAIDs), acetaminophen | Period pain, first step | Many people find them not enough; NSAIDs can irritate the stomach |
| Combined pill, progestogen-only pills (a progesterone-like hormone alone), hormonal IUD | Ongoing pain, contraception wanted | Side effects such as spotting or mood change; pain often returns when stopped 4 |
| GnRH agonists and oral GnRH antagonists (medicines that switch off the ovaries' estrogen for a while, such as elagolix, or relugolix combination therapy) | Pain that persists on first-line hormones | Lower estrogen, so hot flashes and bone loss; often paired with 'add-back' hormones (a low dose of estrogen and progestogen to protect bone and ease hot flashes) 4 |
| Surgery to remove or destroy lesions | Pain not controlled by medicine, deep disease, some fertility cases | Pain can recur; removing ovarian cysts can lower egg reserve (AMH) 4 |
| Hysterectomy | Severe disease when pregnancy is no longer wanted | Not a guaranteed cure if lesions outside the uterus remain |
Pelvic floor physical therapy, a specialist pain service and support for anxiety or low mood can help many people living with long-term pelvic pain. Hormone results such as estradiol on a GnRH treatment show your clinician how far estrogen has been lowered; they do not measure the disease. Our iron deficiency guide makes the key point for heavy periods: "A normal blood count does not rule out iron deficiency", because ferritin empties first. If ferritin is low from heavy bleeding, iron replacement agreed with your clinician can restore your iron stores, but it does not treat the endometriosis, and no guideline recommends a supplement as a treatment for endometriosis.
Endometriosis and pregnancy
Many people with endometriosis conceive without help. Between 30% and 50% have fertility problems 10, through scarring that distorts the tubes and ovaries, inflammation that affects eggs and implantation, and loss of ovarian tissue to cysts 7. Because operating on ovarian cysts can lower ovarian reserve, ESHRE advises weighing that cost before surgery in anyone who wants children 4. Pregnancy does not cure endometriosis, and it carries a slightly higher risk of some complications, such as placenta previa (a placenta lying low over the cervix) and preterm birth 4. The fertility hub covers the tests that matter when you are trying to conceive.
Read before fertility planning
When to see a doctor, and when to go urgently
| Book an appointment if | Go to urgent care or the ER if |
|---|---|
| Period pain stops you working, studying or sleeping | Sudden, severe pelvic or abdominal pain |
| Painkillers have not controlled period pain after 3 months | Pelvic pain with a fever or feeling very unwell |
| Sex is painful, during or after | Fainting or feeling faint with pelvic pain |
| Bowel or bladder pain flares at period time | Bleeding that soaks a pad or tampon every hour for several hours |
| You have tried to conceive for 12 months (6 months if 35 or older) | Pelvic pain with a positive pregnancy test or a missed period |
| Pain keeps coming back after treatment | Sudden breathlessness or chest pain |
These urgent signs apply even if you already have an endometriosis diagnosis: a twisted or burst ovarian cyst, infection and ectopic pregnancy can all start this way. For the wider picture of women's lab work, see blood tests for women and the female hormone panel explained.
Go to an emergency department now for sudden severe pelvic or abdominal pain, pelvic pain with fever, pelvic pain with a positive pregnancy test or a missed period, sudden breathlessness or chest pain, fainting, or bleeding that soaks a pad or tampon every hour for several hours. Discuss any medicine, hormone or supplement with the clinician who knows your history.
Citations
- World Health Organization. Endometriosis fact sheet. 2023.
- NICE guideline NG73. Endometriosis: diagnosis and management. 2017, updated 2024.
- All-Party Parliamentary Group on Endometriosis. Endometriosis in the UK: time for change. 2020.
- Becker CM et al. ESHRE guideline: endometriosis. Human Reproduction Open, 2022.
- Nisenblat V et al. Blood biomarkers for the non-invasive diagnosis of endometriosis. Cochrane Database of Systematic Reviews, 2016.
- NICE guideline NG88. Heavy menstrual bleeding: assessment and management. 2018, updated 2021.
- Zondervan KT, Becker CM, Missmer SA. Endometriosis. New England Journal of Medicine, 2020.
- Shigesi N et al. The association between endometriosis and autoimmune diseases: a systematic review and meta-analysis. Human Reproduction Update, 2019.
- Kvaskoff M et al. Endometriosis and cancer: a systematic review and meta-analysis. Human Reproduction Update, 2021.
- Practice Committee of the American Society for Reproductive Medicine. Endometriosis and infertility: a committee opinion. Fertility and Sterility, 2012.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
