CA 125 test

[sunnysept]

I've been put on the 2 week suspected colorectal cancer pathway by my GP and am waiting for a colonoscopy. My bloods came back as all normal though the CA125 result was this. I'm struggling to understand the comment to be honest about it not excluding malignancy. Is the CA125 marker test unreliable in general and if so, why do it?:

Your result
Se CA 125 level:
5 ku/L

Normal range:
Below 34

Laboratory comment:
If used in context of diagnosis a normal CA125
DOES NOT exclude malignancy.

You can have a normal Ca125 but still have cancer if you do have symptoms, but this does go on to say that if you do have cancer and a normal Ca125, it’s likely to be less aggressive cancer. You can also have high Ca125 and not have cancer btw, it’s the same with the mens PSA test tbh. They are useful tests but not definitive.

An abnormal CA125 test is therefore helpful in identifying women with possible ovarian cancer, especially the most lethal type, but a normal CA125 does not exclude disease. It is reassuring that most women with normal CA125 results were diagnosed at an early stage, despite taking longer to be diagnosed.
https://api.repository.cam.ac.uk/server/api/core/bitstreams/9a4688cc-e514-4736-bffa-361c5731ae79/content#:~:text=28%20An%20abnormal%20CA125%20test,taking%20longer%20to%20be%20diagnosed.

Thanks @ WiseMenSayNothing