Is the blood test called ca 125 to check the uterus for cancer, a good test?

No: It is not. It is often used as such but: a hint of oca requires careful investigation, often surgery. Ca-125 gives many "false positives" so some surgeries would have been unnecessary . This would be ok with those who had oca, but perhaps not with those who did not. Ca-125 also gives "false negatives". This is worse, as the reassurance was misleading! pelvic sonography is a better tool.

CA 125 Biomarker: Ca 125 is a mucin like protein produced by a wide variety of tissues. Ca-125 is most used for ovarian cancer, but elevated ca-125 levels can be found in individuals without ovarian cancer, who have other cancers, including endometrium, breast, and fallopian tube. It is also elevated in benign conditions, so it should never be used alone to make a definitive diagnosis.