Ovarian cancer is diagnosed in around 7,000 women in the UK every year — approximately 20 women every single day. It is the sixth most common cancer in women, and one of the hardest to catch early. The symptoms it produces — bloating, abdominal discomfort, a persistent feeling of fullness, changes in urinary frequency — are vague enough to overlap with a range of far more common and benign conditions, which means diagnosis is frequently delayed. Against this backdrop, the question of whether a blood test can show ovarian cancer is one of the most important questions a woman can ask. The answer is nuanced, honest, and — thanks to significant recent developments in UK clinical guidance — more useful than it has ever been.
The CA125 Blood Test: What It Is and What It Can Tell You
The primary blood test used in the assessment of suspected ovarian cancer in the UK is the CA125 test. CA125 — cancer antigen 125 — is a protein found in the blood that can be elevated in the presence of ovarian cancer. According to Cancer Research UK, CA125 is raised in more than 80% of advanced ovarian cancers and in around 50% of early-stage cases. It is available at GP surgeries across England and is the first-line blood investigation recommended by NICE for women with symptoms suggesting ovarian cancer.
According to Target Ovarian Cancer, a normal CA125 level is usually considered to be below 35 units per millilitre (u/ml). If your level is at 35 u/ml or above, your GP should arrange an urgent pelvic ultrasound scan to look at your ovaries and assess whether any abnormality is present.
It is important to understand what this test does and does not tell you. A raised CA125 is not a diagnosis of ovarian cancer — not by a considerable distance. The elevated protein level indicates inflammation around the pelvis, but it cannot identify the cause. It can be raised in a wide range of conditions that have nothing to do with cancer, including endometriosis, uterine fibroids, ovarian cysts, pelvic inflammatory disease, liver disease, and even menstruation. Being pregnant can also raise CA125 levels. According to Ovarian Cancer Action, nine in ten women with a raised CA125 will not have ovarian cancer.
The converse limitation is equally important: a normal CA125 result does not rule out ovarian cancer. Some women — particularly those with early-stage disease or with certain less common subtypes of ovarian cancer — may have entirely normal CA125 levels despite a cancer being present. Ovarian Cancer Action states explicitly that CA125 levels can be normal in the early stages of ovarian cancer, and that if symptoms persist after a normal result, a woman should return to her GP within a month to discuss whether an ultrasound is needed regardless.
A Significant Step Forward: NICE’s New Age-Based CA125 Thresholds
One of the most clinically important recent developments in this area comes from NICE — the National Institute for Health and Care Excellence — which in 2024–25 proposed a significant update to how CA125 results are interpreted. Currently, a single threshold of 35 IU/ml applies to all women regardless of age. NICE’s updated draft guidance proposes replacing this with personalised, age-based thresholds that reflect how ovarian cancer risk changes as women get older.
According to NICE, the aim of this change is to ensure that women at the greatest risk of ovarian cancer are identified and referred sooner, while reducing unnecessary investigations for women at lower risk. The new approach would allow GPs to make more informed, individualised decisions — using a woman’s age alongside her CA125 level to assess her actual risk profile, rather than applying a blanket threshold. The updated guideline also proposes that women aged 60 and over with unexplained weight loss of more than 5% over six months should receive an urgent investigation or suspected cancer pathway referral, reflecting the higher baseline risk in this age group.
For women and their GPs, this represents a meaningful shift towards more targeted and clinically intelligent use of the CA125 test — and signals clearly that the conversation about CA125 is evolving, not static.
A Larger Study Confirms CA125’s Value — With Important Caveats
A large NIHR-funded study, published in 2024 and analysing data from over 50,000 women who had taken a CA125 test at their GP surgery, found that the test performed considerably better at predicting ovarian cancer in primary care than was previously appreciated. The research, which arose from the Cancer Research UK-funded CanTest Collaborative, found that the test was particularly effective in women aged over 50 — in whom ovarian cancer is most common — and also identified that a raised CA125 in a woman over 50 in whom ovarian cancer has been excluded should prompt investigation for other cancers, including those of the pancreas and lung.
The researchers developed a model to estimate an individual woman’s probability of ovarian cancer based on her age and CA125 result — a more nuanced, personalised risk tool than the current binary threshold approach. While this model is not yet in routine clinical use, it signals clearly where the UK diagnostic pathway for ovarian cancer is heading: towards individualised, risk-stratified assessment rather than a one-size-fits-all approach.
A patient seen at our Birmingham clinic — a woman in her early fifties — presented with several weeks of persistent bloating and a sensation of abdominal fullness that she had attributed to dietary changes. A private blood test including CA125 revealed a level of 58 u/ml. She was referred promptly for an urgent pelvic ultrasound, which identified a suspicious ovarian mass requiring specialist assessment. Early identification at this stage gave her access to treatment options that would not have been available had her symptoms been dismissed for another several months.
Additional Blood Tests Used in Ovarian Cancer Assessment
CA125 is the primary blood marker, but it is not the only one. Depending on clinical circumstances — particularly a woman’s age and the nature of her symptoms — a GP or specialist may also request:
HE4 and the ROMA Algorithm
Human epididymis protein 4 (HE4) is a newer tumour marker that has been shown to be elevated in ovarian cancer. Research funded by Wellbeing of Women and carried out by Dr Garth Funston at the University of Manchester — examining blood samples from 1,247 patients — found that HE4 levels, when combined with CA125 within an algorithm called ROMA (Risk of Ovarian Malignancy Algorithm), could improve the detection of ovarian cancer in primary care, particularly in women under 50. The ROMA algorithm uses both markers alongside menopausal status to generate a risk score — offering a more accurate picture than CA125 alone in certain groups. This approach has been studied in hospital settings for some time, but Wellbeing of Women’s research is among the first to demonstrate its utility in a primary care environment.
AFP, hCG, and LDH for Younger Women
For women aged 40 and under, Cancer Research UK notes that specialists may also check the levels of alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG), and lactate dehydrogenase (LDH). These markers are associated with germ cell tumours — a rarer type of ovarian cancer more commonly seen in younger women — and form part of the extended assessment for this age group.
CEA and CA19-9
According to Cancer Research UK’s diagnostic guidance, specialists may also measure CEA (carcinoembryonic antigen) and CA19-9 in certain cases — particularly where there is a possibility that another cancer type has spread to the ovaries, rather than the tumour originating there. These markers help build a more complete picture of what is driving any ovarian abnormality found on imaging.
What About the UKCTOCS Screening Trial?
The UK Collaborative Trial of Ovarian Cancer Screening (UKCTOCS) was a large long-term study that investigated whether CA125 testing — either alone or combined with ultrasound — could serve as a general population screening tool for ovarian cancer. The trial’s conclusions, reported by Cancer Research UK, were sobering: while the CA125 blood test did detect some cancers earlier, this earlier detection did not translate into a statistically significant saving of lives. Ultrasound screening also failed to reduce mortality. On the basis of these findings, neither test is recommended as a routine screening tool for the general population in the UK.
This does not mean CA125 is without value — it means it is best used as a diagnostic investigation in women with symptoms, not as a general screening test in asymptomatic women. The distinction matters enormously, both for clinical practice and for understanding what to expect when a GP requests this test.
Symptoms That Should Prompt a CA125 Blood Test
According to NICE clinical guidelines, a CA125 blood test should be offered to any woman — particularly those aged 50 or over — who presents with any of the following symptoms, especially if they are frequent, persistent, or new:
- Persistent abdominal bloating, particularly if it comes on most days
- A feeling of fullness or difficulty eating normally, even when eating smaller amounts than usual
- Pelvic or abdominal pain that is new or unexPlained
- Needing to urinate more urgently or more frequently than usual
- Unexplained weight loss
- Changes in bowel habit — particularly new constipation — that have no other clear explanation
- Extreme fatigue without a clear cause
- Postmenopausal bleeding
It is worth emphasising what Target Ovarian Cancer and NICE guidance both make clear: if your CA125 result comes back normal but your symptoms persist, you should return to your GP within a month and discuss whether a pelvic ultrasound is warranted regardless. Symptoms, not test results alone, should drive the clinical decision-making process in suspected ovarian cancer.
At The Private GP in Birmingham, a face-to-face GP consultation gives you direct access to a GMC-registered doctor who will take your symptoms seriously, arrange a CA125 blood test with same-day results, and refer promptly for urgent ultrasound where the clinical picture warrants it. You do not need to wait weeks for an NHS appointment when concerns like these deserve prompt attention. Book today.
If You Have a Family History or BRCA Gene Mutation
Women with a BRCA1 or BRCA2 gene mutation, or a strong family history of ovarian or breast cancer, face a significantly elevated lifetime risk of ovarian cancer and may be offered more intensive surveillance — including six-monthly CA125 tests and pelvic ultrasounds — through specialist family history clinics. The NICE 2024 guideline on identifying and managing familial and genetic risk of ovarian cancer provides detailed guidance on this pathway. If you have a relevant family history and have not yet been assessed for your genetic risk, discussing this with your GP is an important step. A private GP consultation can facilitate prompt referral to a clinical genetics service where appropriate.
Frequently Asked Questions
- What does a raised CA125 mean?
A CA125 above 35 u/ml means the level of the CA125 protein in your blood is higher than the normal range. According to Target Ovarian Cancer and NICE guidelines, this should prompt your GP to arrange an urgent pelvic ultrasound scan. However, a raised CA125 does not mean you have ovarian cancer — nine in ten women with a raised result will not have cancer, and elevated CA125 can be caused by many benign conditions including endometriosis, fibroids, ovarian cysts, and pelvic inflammatory disease. It is a prompt for investigation, not a diagnosis.
- Can a blood test rule out ovarian cancer?
No blood test can definitively rule out ovarian cancer. A normal CA125 result provides some reassurance, but it does not exclude the diagnosis — particularly at an early stage or in less common tumour types where CA125 may remain within the normal range. According to Ovarian Cancer Action, if your symptoms persist after a normal CA125 result, you should return to your GP within a month to discuss whether a pelvic ultrasound is still needed. Symptoms must drive clinical decision-making alongside test results.
- What is the difference between CA125 and HE4?
CA125 and HE4 are both tumour markers associated with ovarian cancer. CA125 is the established first-line test in UK primary care. HE4 is a newer marker that, when combined with CA125 within the ROMA algorithm, has been shown to improve detection accuracy — particularly in women under 50, where CA125 alone is less reliable due to benign conditions that commonly elevate it. HE4-based testing is not yet in routine use at UK GP surgeries, but research funded by Wellbeing of Women suggests it may enter the primary care diagnostic pathway in the future.
- Is there a screening test for ovarian cancer in the UK?
There is currently no national ovarian cancer screening programme in the UK for the general population. The UKCTOCS trial, which evaluated CA125 blood testing and ultrasound as screening tools, found that while CA125 detected some cancers earlier, this did not translate into a significant reduction in deaths — and the tests were not recommended for routine screening. Women at high genetic risk (BRCA1/2 mutation or strong family history) are offered surveillance through specialist clinics. Any woman with persistent symptoms should seek a GP assessment and request a CA125 blood test. At The Private GP, a private blood test in Birmingham including CA125 is available with same-day results.
- How long does a CA125 blood test take to get results?
At The Private GP in Birmingham, CA125 blood test results are typically available the same day, with a GMC-registered GP on hand to interpret what the result means for you specifically — including whether further investigation is needed and how urgently. If you are having a CA125 test through your NHS GP, your surgery will advise on turnaround time, which is typically within one to two weeks. If you do not hear within two weeks, Target Ovarian Cancer advises calling your GP to follow up. You can also register for online access to your medical record through your GP surgery or the NHS app.