Blood test cannot find out which kind of cancer is suffered from, but blood test can check tumor markers, through which tumor markers can suspect whether related tumor occurs. The most common is methemoglobin. If methemoglobin is higher than 500mg/L or 1000mg/L for more than 2-3 months, it is necessary to suspect whether the patient is suffering from liver cancer, and further ultrasound or CT examination is needed, and finally, pathological diagnosis by puncture. CA12-5 is often suspected to be a tumor of the ovary, but further examination, such as ultrasound, CT, puncture and pathological examination, is needed to confirm the diagnosis. However, further examinations such as ultrasound, CT, aspiration, pathological examination are needed to confirm the diagnosis. Therefore, blood test cannot diagnose tumor, but it can check tumor markers for early suspicion, further related examination, and finally confirm the diagnosis through medical examination.