CA 125: what it is, what it tells you and when it’s tested

CA 125 is a protein found in small amounts in your blood. Some cancers, mainly of the ovary, make more of it. But it also often rises for common, benign reasons, such as your period or endometriosis. That is why it is not used to look for cancer in women who feel well: it is mainly used with an ultrasound scan and to follow a disease that is already known.

When it’s tested

Doctors mostly order it in two cases. If an ultrasound scan finds a mass on an ovary, CA 125 helps, together with the scan, to work out what it is. If a woman has had ovarian cancer, it is used to follow treatment and check-ups.

It is not a screening test. Italian and international guidelines advise against using it to look for ovarian cancer in women who feel well. A large trial showed that this screening does not reduce deaths, and it leads to unnecessary surgery.

That is why Rosa does not test it. The Rosa panel is a general prevention check-up, not a cancer test: it looks at your heart, metabolism, liver, kidneys, thyroid and blood.

What it tells you, and what it does not

A high CA 125 does not mean cancer. Your period, pregnancy, endometriosis, fibroids and pelvic inflammation often raise it. Some liver, heart and kidney conditions raise it too.

A normal CA 125 does not rule out cancer. Early on, many ovarian cancers do not raise it.

What matters most is how it changes over time, at the same lab, and always together with the scan and an examination.

Your doctor reads it together with other tests:

Normal CA 125 levels

The lab decides what is normal. Many lab reports give a CA 125 below 35 U/mL.

During your period and in pregnancy it can be higher. If the value is just above the limit, your doctor may have it repeated at another time of the month.

Each lab uses its own method, and the same blood can give slightly different numbers at two labs. To follow it over time, it is best to use the same lab every time.

Why CA 125 can be high

The cause is often benign. The most common come first.

CA 125 and ovarian masses

If an ultrasound scan finds a mass on an ovary, your gynaecologist may ask for CA 125. It is read together with the scan, never on its own.

Age matters a lot. Before the menopause, CA 125 often rises for benign reasons, such as endometriosis, so it tells you less. After the menopause it is more useful.

If you have had ovarian cancer, CA 125 is used to follow treatment and check-ups, as your oncologist decides.

If your CA 125 is above the limit

Try not to worry: it is common, and often benign. Where to start:

When to talk to a doctor

Talk to your doctor if:

Frequently asked questions

High CA 125: what are the benign causes? The most common are your period, pregnancy, endometriosis, fibroids and pelvic inflammation. Liver, heart and kidney conditions can raise it too.

What are normal CA 125 levels? Many lab reports give a value below 35 U/mL. The range on your own report is what counts.

Does CA 125 rise during your period? Yes, it can rise during the days of your period. If the value is just high, your doctor may have it repeated at another time of the month.

CA 125 and endometriosis: what is the link? Endometriosis often raises CA 125, sometimes by a lot. That is why the value is read with your gynaecologist, together with an ultrasound scan.

Is CA 125 useful if ovarian cancer runs in my family? Not on its own. If several relatives have had ovarian or breast cancer, talk to your doctor: they can refer you for genetic counselling and to a centre that decides the right check-ups for you.

Does Rosa test CA 125? No. Rosa is a general prevention check-up and does not include tumour markers. If your doctor thinks CA 125 is useful, they order it separately.

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