What to expect during a blood test for bowel cancer
Understand how a blood test supports bowel cancer screening, what the process involves, and what your results may reveal.
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Blood tests aren’t used to diagnose bowel cancer on their own, but they can reveal signs like inflammation, anaemia, or abnormal liver function that suggest something may be wrong. Often, your doctor will order a blood test alongside other screening tools, such as a stool test (iFOBT) or a colonoscopy, to help build a clearer picture of your bowel health. The procedure itself is quick, low-risk, and typically performed at a medical centre or pathology clinic. While a blood test for bowel cancer can’t confirm bowel cancer, the results help your doctor decide whether more testing is needed or if treatment is working as planned.
What markers are checked in a blood test for bowel cancer?
- CEA (Carcinoembryonic Antigen) – CEA is a protein that may be elevated in some people with bowel cancer, particularly in more advanced cases. While not specific to cancer, high levels can prompt doctors to order additional tests or monitor known conditions.
- Full blood count (FBC) – An FBC checks the number of red blood cells in your blood. Low levels might point to anaemia, which can result from long-term internal bleeding in the bowel, a possible sign that further bowel investigations are necessary.
- Liver function tests – These tests measure enzymes and proteins related to liver health. Since bowel cancer can potentially spread to the liver, abnormal liver results may indicate secondary cancer or inflammation that needs further investigation.
- Inflammation markers (CRP or ESR) – CRP and ESR tests check for inflammation in the body. While not specific to bowel cancer, elevated results can suggest infection, inflammatory bowel disease, or even cancer, depending on your overall symptoms and history.
How should you prepare for a blood test for bowel cancer?
- Ask about fasting requirements – Many blood tests for bowel cancer don’t require fasting, but some may, depending on what your doctor is checking. It’s best to confirm any special instructions with your GP or the pathology clinic before your appointment.
- Take your regular medications – In most cases, you can continue taking your usual medications as prescribed before the test. However, if you’re taking blood thinners or any new medications, check with your GP in case they need to delay or adjust the test.
- Bring your Medicare and referral info – If your GP or specialist has referred you, make sure to bring the referral form and your Medicare card. Most pathology clinics will require both to process the test and ensure it’s covered under the public healthcare system.
- Wear a short-sleeved shirt – A short-sleeved top makes it easier for the phlebotomist to access your arm, which can help the process go faster and more smoothly. You’ll usually be asked to stay seated and relaxed during the blood collection process.
How should you prepare for a blood test for bowel cancer?
- Ask about fasting requirements – Many blood tests for bowel cancer don’t require fasting, but some may, depending on what your doctor is checking. It’s best to confirm any special instructions with your GP or the pathology clinic before your appointment.
- Take your regular medications – In most cases, you can continue taking your usual medications as prescribed before the test. However, if you’re taking blood thinners or any new medications, check with your GP in case they need to delay or adjust the test.
- Bring your Medicare and referral info – If your GP or specialist has referred you, make sure to bring the referral form and your Medicare card. Most pathology clinics will require both to process the test and ensure it’s covered under the public healthcare system.
- Wear a short-sleeved shirt – A short-sleeved top makes it easier for the phlebotomist to access your arm, which can help the process go faster and more smoothly. You’ll usually be asked to stay seated and relaxed during the blood collection process.
What happens during the test itself?
- You’ll be seated and asked to relax – Once you arrive, the clinician will confirm your details and help you feel at ease. You’ll be seated comfortably, and the nurse will explain what to expect before starting the blood collection process.
- A tourniquet is applied to your upper arm – The clinician will carefully wrap a tourniquet around your upper arm to help your veins become more visible. This makes it easier to draw the blood safely and with as little discomfort as possible.
- Blood is drawn using a fine needle – A thin needle is used to collect blood, usually from your inner arm. Depending on what markers are being checked, a few tubes may be filled. The entire process usually takes less than five minutes.
- A dressing is applied post-test – After blood is drawn, the needle is removed, and a cotton pad or bandage is applied. Some people feel a little pressure or light-headed briefly, but most can return to normal activity soon after the test.
What do the results mean?
- Abnormal results aren’t always cancer – Elevated markers like CEA or inflammation levels don’t automatically mean that cancer is present. They can also appear due to infections, smoking, or other non-cancerous bowel conditions like Crohn’s disease or IBS.
- Results guide further testing – If your results show any concerns, your doctor may recommend further investigations such as a colonoscopy or imaging scan. These help confirm whether symptoms or blood markers point to a cancerous or benign condition.
- Used to monitor cancer treatment – For patients already diagnosed with bowel cancer, blood tests are often used to monitor how well treatment is working. Changes in markers over time can alert your medical team to possible recurrence or complications.
- Discuss all results with your doctor – Only your General Practitioner or specialist can interpret your blood test results in full context. They’ll explain what the findings mean, whether additional tests are needed, and what your next steps might look like.
What do the results mean?
- Abnormal results aren’t always cancer – Elevated markers like CEA or inflammation levels don’t automatically mean that cancer is present. They can also appear due to infections, smoking, or other non-cancerous bowel conditions like Crohn’s disease or IBS.
- Results guide further testing – If your results show any concerns, your doctor may recommend further investigations such as a colonoscopy or imaging scan. These help confirm whether symptoms or blood markers point to a cancerous or benign condition.
- Used to monitor cancer treatment – For patients already diagnosed with bowel cancer, blood tests are often used to monitor how well treatment is working. Changes in markers over time can alert your medical team to possible recurrence or complications.
- Discuss all results with your doctor – Only your General Practitioner or specialist can interpret your blood test results in full context. They’ll explain what the findings mean, whether additional tests are needed, and what your next steps might look like.
When should you ask for a blood test?
- Persistent bowel symptoms – If there’s blood in your stool, ongoing abdominal pain, fatigue, or unexplained weight loss, talk to your GP. These symptoms may be linked to bowel cancer or other gastrointestinal issues.
- Family history of bowel cancer – If you have a close relative who’s had bowel cancer, your risk may be higher. Your doctor might recommend blood testing and earlier or more frequent screening to stay on top of your health.
- Following up on abnormal stool tests – If you’ve had a positive iFOBT result (stool test), your doctor may include a blood test in your follow-up to check for other signs of disease and determine whether a colonoscopy is needed.
- Ongoing monitoring post-treatment – If you’ve been treated for bowel cancer in the past, blood tests may be part of your regular follow-up care. These tests help ensure the cancer hasn’t returned and allow early intervention.
Thinking about getting a blood test for bowel cancer?
If you’ve been dealing with unexplained digestive issues, have a family history of bowel cancer, or simply want peace of mind, it’s worth taking that next step. A blood test for bowel cancer might not provide all the answers on its own, but it can offer valuable clues that help guide your care.
Even if you’re feeling well, early bowel cancer screening can make a real difference, especially when combined with other tools like stool tests or colonoscopies. Understanding your results and knowing what they mean can help you make more informed decisions about your health.
If something doesn’t feel quite right or you’ve been putting off that conversation, now might be the time to speak with your GP or gastrointestinal specialist. Taking action today can lead to better outcomes tomorrow.
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FAQs
Does a high CEA level always mean cancer?
Not necessarily. CEA can be elevated due to several non-cancerous reasons such as infection, inflammation, or smoking. It’s only one part of the bigger picture and must be interpreted with other clinical findings.
Do I need someone to stay with me at home afterwards?
Yes. Because sedation can impair your alertness for several hours, having someone with you until the next day is strongly recommended for safety.
Will I get my results straight away?
Most standard blood test results are available within 1–3 days. Your doctor will contact you to explain the results and decide whether any further action or testing is needed.
Can I still get a blood test if I’m feeling well?
Yes. Blood tests may still be recommended even without obvious symptoms, especially if you have a family history of bowel cancer or you’re due for routine screening. Early checks can help detect issues before symptoms appear.