Blood Drug Testing

How accurate are blood tests for detecting cancer, can it be trusted or can it miss some forms of cancer?

Public Comments

1. There is no single blood test for cancer. Most types of cancer can not be detected through a blood test. You would need to be more specific about what kind of cancer you are worried about.
2. Some types of cancer cannot be detected by blood tests. I knew someone whose cancer went undetected for some eighteen months despite various medical investigations, the Doctors finally said it was 'deep seated'. He sadly passed away a couple of years ago. I would say, however the scare stories are a small minority and most people are diagnosed and treated when appropriate. Early detection is the key, as is the type and location of the cancer. It's never good news, but not always a death sentence. I wish you better health.
3. Different cancers have different tests. Each one has what is called a marker , so if you are having a test to look for a particular cancer the test will be to look for that marker in the blood. If you are having a standard blood test which usually check's for anaemia liver function etc a cancer may not be picked up although there can be clues appear in a standard blood test that need further investigation. Basically a blood test will only pick up what a doctor has requested to be checked.
4. Not very accurate if used solely on their own. Usually an analysis of other symptoms along with a range of blood tests may confirm that there is something not quite right, which may require further detailed tests and evaluations. For instance a Full Blood Count test gives a lot of information, which in conjunction with other symptoms may establish the need for more specific tests that could identify the particular ailment more precisely. FBC measures include; - the amount of haemoglobin in the blood; - the number of red blood cells (red cell count); - the percentage of blood cells as a proportion of the total blood volume (haematocrit or packed cell volume); - the volume of red blood cells (mean cell volume); - the average amount of haemoglobin in the red blood cells (known as mean cell haemoglobin); - the number of white blood cells (white cell count); - the percentages of the different types of white blood cells (leucocyte differential count); and - the number of platelets.
5. Most blood tests cannot directly find cancerous cells. It can show if your cell counts are low, your iron is low, or other symptoms of cancer though.
6. I assume you are talking about blood tests for tumour markers? Many cancers, or the cells they invade, release substances into the bloodstream which can be identified and measured. These substances are called tumour markers. However, although some markers are specific to only one type of cancer the majority are not and are only part of the diagnostic process. A good example is Prostate specific antigen (PSA) which is a tumour marker for prostate cancer in men. 66% of men with an elevated PSA blood test, after further tests do not have cancer, but instead some other problem with their prostate. I am not being critical of tumour markers, they are incredibly valuable in reaching a diagnosis of cancer, but are only one part of the jigsaw. I hope that helps answer your question.
7. Blood tests only give some indications. From the blood tests, one can not conclude about Cancer. However, in cases of leukemia, blood test may give very strong indication. For conclusion of Cancers called Tumors only biopsy can give conclusive results. While for blood cancers like leukemia, only Bone Marrow can give conclusive results.
8. Many older men get a psa test annually. A high reading doens't mean you Do have prostate cancer and a low reading doens't mean you don't. There is another test, CEA, which a friend has done every year . he had rectal cancer.
9. Tumour marker studies are generally used to monitor progression in cancer, the PSA being the exception. The PSA is used for detection. Tumour marker studies should never be used to diagnose cancer as yes they certainly can miss several different types of cancer. They should never replace conventional medical diagnosis if cancer is suspected. Having said that however, some tumour markers such as Ca 19-9 are increasingly being used as a screening test even if cancer is not suspected. Although it is primarily used as a progression marker, I have seen it detect many a GIT and bowel cancer early in otherwise normal patients. So in that respect it has been a Godsend to many people. Personally, I have a Ca19-9 done yearly (just like I have a pap smear every 2 years). It doesn't give an all clear at all but it can aid in early detection.
10. the blood tests are backed up with scans and biopsies