You would actually have to have cancer in your blood. Blood tests can show signs of cancer. For example, if your white cell count is elevated, your body is fighting against something. Unfortunately, it could be fighting off an infection or something else. Doctors need to test a specific organ for cancer.
I have had urinary symptoms for a month and a half all urinary tests come back negative im scheduled for a cysto on the 23rd. Im in severe pain I have been to three ers all say cannot explain need mri please help
Blood tests screen for particular things, so if you want a screening for cancer, you would need to tell your doctor and they would test certain aspects of your blood. There really hasn't been a very reliable blood test for cancer, as different cancers present themselves in different ways. Your doctor will ask where you think the cancer is.
It all depends what type of blood work you are getting. If you feel that you have cancer talk it over with your doctor and they might do a Pet Scan first and then a MRI.
If you feel this way, you need to consult your physician. Many people do not because they are afraid of what they may hear. Its better to take care of it as soon as possible if it comes out to be. Only a Full Blood Count can seek this.