Can a Blood Test Detect Cancer? The Role of Blood Tests in Early Cancer Diagnosis
Blood tests are integral to diagnosing various medical conditions, including cancer. If cancer is suspected, blood tests are often part of the investigative process. These tests range from routine checks, like full blood counts and kidney function, to specialised blood tests for specific cancers.
While blood tests are crucial in diagnosing cancer, they are not standalone. Results are usually considered alongside symptoms, scan results, and often a biopsy. It's important to remember that blood tests are not foolproof—a normal result doesn't always rule out cancer (a false negative), and an abnormal result doesn't always confirm it (a false positive).
How Can Routine Blood Tests Help?
Routine blood tests can sometimes reveal signs of serious conditions, prompting further investigation. People who are experiencing vague or mild symptoms often undergo a range of routine blood tests checking things like renal function, haemoglobin levels, or liver function, and abnormalities in these usually prompt further tests to find out exactly what is causing the problem.
A good example of this is the detection of bowel cancer. A tumour in the bowel usually causes some degree of bleeding. Whilst you may not actually see blood in the stool, the tumour may be causing microscopic amounts of blood to continually be lost. This results in low haemoglobin levels (anaemia) and low iron levels. For this reason, current guidelines advise that any man or postmenopausal woman who is found to have an iron deficiency anaemia - in the absence of another obvious cause - should be investigated for bowel cancer with stool tests and/or a colonoscopy.
There are of course many other reasons why someone may have an iron deficiency anaemia. Still, bowel cancer is often diagnosed like this - with the incidental finding of a low haemoglobin.
Tumour Markers
Specific blood tests, known as tumour markers, are associated with different cancers. These markers include CEA for bowel cancer, Alpha-fetoprotein for liver cancer, Ca19-9 for pancreatic cancer, and Ca15-3 for breast cancer. Generally, these tests are used to monitor existing cancer rather than for initial screening. Two notable exceptions are PSA for prostate cancer and Ca125 for ovarian cancer, which are more commonly used for screening.
PSA and Ca125 Screening
Men over 50 in the UK can request a PSA test for prostate cancer. In these circumstances, the man requesting the test should be advised that a raised reading does not mean that there is definitely cancer but it would usually prompt a physical examination of the prostate, a repeat of the blood test and then possible further investigations including MRI scan and prostate biopsy.
Ca125 is often conducted on women who present with vague abdominal symptoms such as bloating or other symptoms that may otherwise be attributed to ‘irritable bowel syndrome’. Although, just as with the other tests, Ca125 can be normal in the presence of cancer or raised in non-cancerous conditions such as endometriosis, it is widely used to improve the rate of early diagnosis for ovarian cancer. Caught early, ovarian cancer is very treatable, but it often presents very late because it causes only mild or no symptoms in the early stages.
The Importance of Blood Tests in Cancer Detection
As you can see from the above, blood tests play a key role in the diagnosis and monitoring of cancer. As a general rule of thumb, if you feel well and your blood tests are normal, then there is usually no problem. If you feel unwell, particularly if you have any symptoms that are steadily worsening, then you should always see a doctor even if all of your blood tests are normal.
Learn how One Day Tests helped Andrzej Kubinski detect early signs of kidney cancer.
“If I had not visited One Day Tests and got a blood test then my condition would have got a lot worse. I’m so grateful I went and got my blood tested.”
Basic Markers of Full Body Health
Frequently Asked Questions
Would cancer show up in routine blood work?
Sometimes evidence of cancer is picked up on routine blood tests. An example of this is bowel cancer which is often detected when a low haemoglobin is found unexpectedly (this results from microscopic bleeding into the gut). However, not all cancers will show up in routine blood tests so, even if all routine tests are normal, you should speak to a doctor if you have symptoms that you are worried about.
Would a full blood count show anything serious?
A full blood count gives us lots of information. For example, a low haemoglobin in the full blood count usually prompts further investigation to exclude bowel cancer. The full blood count also looks at the different cell types of the immune system and abnormalities in these may indicate different types of blood cancer (such as leukaemia).
Similarly, abnormal levels of platelets (either high or low) are associated with a variety of different cancers. The full blood count by itself does not usually give a diagnosis of cancer, but abnormalities in the full blood count are often the starting point for further investigation.
Can you have normal blood work and still have cancer?
Yes, this is fairly common so, even if blood tests are normal, you should see a doctor if you are worried about your symptoms.
What can doctors tell from a full blood test?
Blood tests give an enormous range of information to doctors ranging from your state of health, problems with specific organs, which medications may or may not be safe to use, and evidence of problems such as inflammation or infection.
How long can you have cancer without knowing?
This depends on the type of cancer, how aggressive it is and where it is located. Many men with prostate cancer will never know they have it and will die of something else (such as old age) before the cancer ever comes to their attention. Conversely, some cancers are very aggressive and may cause death within weeks of symptoms becoming apparent.
What is the hardest cancer to detect?
Many cancers can be difficult to detect but two cancers that are notorious for presenting late are ovarian cancer and pancreatic cancer. In general, cancers cause symptoms as they grow because they cause damage or put pressure on other parts of the body causing pain, loss of function or other symptoms. Because the ovaries and the pancreas sit deep in the abdominal cavity, they have lots of room to grow before they cause any symptoms.
What is the biggest indicator of cancer?
There is no single indicator for cancer, every cancer presents differently. Having said that, unexpected weight loss is a symptom that doctors never ignore because it is often associated with cancer.
What are the 7 warning signs of blood cancer?
This depends on the type of blood cancer. Some chronic forms of leukaemia cause no signs or symptoms and may never actually cause any problems. Classical signs of other blood cancers include drenching sweats at night, unexpected weight loss, unexplained fever, easy bruising or bleeding, and pallor and shortness of breath (related to underlying anaemia).
Which cancer has no symptoms?
Many cancers may have no symptoms, particularly in the early stages.
What tests are done to check for cancer?
A diagnosis of cancer usually involves some combination of a physical exam, blood tests, scans or x-rays, and a biopsy.
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