A colonoscopy may be recommended when your doctor needs to investigate symptoms affecting your bowel, follow up an abnormal test result, check for polyps, or assess your risk of bowel cancer. It is one of the most useful tests for examining the inside of the large bowel and rectum because it allows the specialist to see the bowel lining directly and remove polyps where clinically appropriate.
Not everyone with bowel symptoms needs a colonoscopy. Many symptoms can be caused by common conditions such as haemorrhoids, constipation, diet changes, infections or irritable bowel syndrome. However, some symptoms should not be ignored, especially if they are new, persistent, worsening, unexplained, or occur with other risk factors.
This guide explains the signs that may lead your GP to recommend a colonoscopy, what a colonoscopy can help detect, and when you should seek medical advice sooner rather than waiting for routine screening.
Article index
- What is a colonoscopy?
- When might your doctor recommend a colonoscopy?
- Rectal bleeding or blood in the stool
- Persistent change in bowel habits
- Ongoing abdominal pain, bloating or cramping
- Unexplained iron deficiency anaemia
- Unexplained weight loss or ongoing fatigue
- Positive bowel screening test result
- Family history of bowel cancer or polyps
- Previous bowel polyps or surveillance colonoscopy
- Inflammatory bowel disease symptoms or monitoring
- Do younger adults ever need a colonoscopy?
- What can a colonoscopy detect?
- What happens if your GP refers you?
- How Direct Endoscopy can help
- Final thoughts
What is a colonoscopy?
A colonoscopy is a procedure that allows a specialist to examine the inside of the large bowel and rectum using a thin, flexible tube with a camera. It is commonly performed under sedation or anaesthesia so that patients are comfortable during the procedure.
During a colonoscopy, the specialist can look for causes of bowel symptoms such as bleeding, inflammation, ulcers, diverticular disease, polyps or bowel cancer. If polyps are found, they can often be removed during the same procedure and sent for pathology testing. Biopsies may also be taken if an area of the bowel lining needs closer examination.
Colonoscopy is different from a bowel screening test. A bowel screening test looks for hidden blood in the stool. A colonoscopy allows the doctor to examine the bowel directly and investigate why symptoms or abnormal test results may be occurring.
When might your doctor recommend a colonoscopy?
Your GP may recommend a colonoscopy when symptoms, test results or risk factors suggest that the bowel needs to be examined more closely. This does not automatically mean you have bowel cancer. In many cases, colonoscopy finds non-cancerous causes of symptoms, such as haemorrhoids, inflammation, diverticular disease or benign polyps.
However, colonoscopy is often recommended when your doctor needs to rule out more serious conditions or detect problems early. It may be considered if you have rectal bleeding, a persistent change in bowel habits, unexplained iron deficiency anaemia, a positive bowel screening test, a family history of bowel cancer, previous polyps, or symptoms that have not improved with initial treatment.
The key point is persistence. A one-off change in bowel habits after a different meal or short illness may not be concerning. Symptoms that continue, recur, worsen, or cannot be explained should be discussed with your GP.
Rectal bleeding or blood in the stool
Blood in the stool is one of the most common reasons people are referred for colonoscopy. It may appear as bright red blood on toilet paper, blood mixed with the stool, dark red blood, or black, tarry stools. The appearance of blood can sometimes give doctors clues about where bleeding may be coming from, but it is not always possible to know the cause without assessment.
Rectal bleeding can be caused by haemorrhoids, anal fissures, inflammation, infection, diverticular disease, polyps or bowel cancer. Because the causes range from minor to serious, bleeding should not be dismissed, especially if it is new, persistent or occurs with other symptoms.
You should speak with your GP if you notice blood in your stool, bleeding from the rectum, or repeated bleeding when opening your bowels. Seek urgent medical care if bleeding is heavy, if stools are black and tar-like, or if bleeding occurs with dizziness, fainting, severe abdominal pain or weakness.
Cancer Australia lists blood in the stool as one of the common symptoms that can occur with bowel cancer, although bowel cancer may also have no symptoms in its early stages. You can read more about bowel cancer symptoms from Cancer Australia.
Persistent change in bowel habits
A change in bowel habits means your usual pattern has changed. This may include ongoing diarrhoea, constipation, needing to go more often, feeling that the bowel does not empty properly, or noticing a change in the shape or consistency of your stool.
Everyone’s bowel habits are different, so the important issue is what is unusual for you. Some people naturally open their bowels several times a day, while others go every couple of days. A change becomes more concerning when it is persistent, unexplained, worsening or associated with other symptoms such as bleeding, abdominal pain, weight loss or anaemia.
Your GP may recommend a colonoscopy if a change in bowel habit continues for several weeks, keeps returning, or cannot be explained by diet, medication, stress, infection or another obvious cause. Colonoscopy can help investigate whether there is inflammation, narrowing, polyps, cancer or another bowel condition.
Cancer Council Australia includes changes in bowel habit, blood in the stool, abdominal pain, bloating, weight loss and anaemia among bowel cancer symptoms. You can read more from Cancer Council Australia.
Ongoing abdominal pain, bloating or cramping
Abdominal pain, bloating and cramping are common symptoms and are not always related to the bowel. They can be caused by diet, constipation, infections, irritable bowel syndrome, reflux, gallbladder problems, gynaecological conditions or many other causes.
However, your GP may consider colonoscopy if abdominal symptoms are persistent, unexplained, associated with bowel habit changes, or occur with bleeding, anaemia, weight loss or family history. Pain that is new and ongoing should be assessed rather than ignored.
It is also important to consider the pattern of symptoms. For example, occasional bloating after certain foods may suggest a different pathway from progressive abdominal pain with rectal bleeding and weight loss. Your GP can decide whether colonoscopy, blood tests, stool tests, imaging, gastroscopy or another investigation is most appropriate.
Unexplained iron deficiency anaemia
Iron deficiency anaemia can occur when the body does not have enough iron to make healthy red blood cells. Some people notice tiredness, weakness, shortness of breath, dizziness, headaches, pale skin or reduced exercise tolerance. Others only find out after a blood test.
There are many possible causes of iron deficiency, including diet, heavy menstrual bleeding, pregnancy, malabsorption and blood loss from the digestive tract. In some adults, unexplained iron deficiency anaemia may lead a doctor to investigate the bowel, especially if there is no obvious cause.
A colonoscopy may be recommended to check whether there is bleeding from polyps, inflammation, bowel cancer or another condition. In some cases, a gastroscopy may also be recommended to examine the upper digestive tract.
If your blood tests show iron deficiency or anaemia, do not assume the cause. Speak with your GP about whether further investigation is needed.
Unexplained weight loss or ongoing fatigue
Unexplained weight loss means losing weight without trying, especially when there has been no major change in diet, activity or lifestyle. Ongoing fatigue can also be important, particularly if it is new, persistent or linked with anaemia, appetite changes or bowel symptoms.
These symptoms can be caused by many conditions and do not automatically mean bowel cancer. However, when they occur with bowel habit changes, rectal bleeding, abdominal pain or iron deficiency anaemia, your GP may recommend further investigation, including colonoscopy.
The aim is to find the cause early. If the result is not serious, that can be reassuring. If a condition does need treatment, earlier diagnosis can help guide the next step sooner.
Positive bowel screening test result
A positive bowel screening test is one of the most common reasons for colonoscopy referral. The National Bowel Cancer Screening Program uses a home test called a faecal occult blood test, or FOBT, to look for tiny amounts of blood in the stool that may not be visible.
A positive result does not mean you have bowel cancer. It means blood has been detected and the cause should be investigated. Possible causes include haemorrhoids, polyps, inflammation and bowel cancer. Colonoscopy is usually recommended because it allows the specialist to examine the bowel directly.
Eligible Australians aged 45 to 74 can take part in the National Bowel Cancer Screening Program every two years. People aged 50 to 74 are sent a kit automatically, while people aged 45 to 49 can request their first free kit. You can read more about the program from the Australian Government Department of Health.
If you receive a positive result, do not panic, but do not ignore it. Make an appointment with your GP to discuss the next step.
Family history of bowel cancer or polyps
Your doctor may recommend earlier or more regular bowel investigation if you have a family history of bowel cancer or certain types of bowel polyps. The level of risk depends on which relative was affected, how old they were at diagnosis, and whether more than one family member has had bowel cancer.
A parent, brother, sister or child with bowel cancer is usually more significant than a more distant relative. Risk may also be higher when a close relative was diagnosed at a younger age, particularly under 50, or when several relatives on the same side of the family have had bowel cancer.
Family history does not mean you will definitely develop bowel cancer. However, it may change when screening should start and whether colonoscopy is preferred over routine stool testing. Cancer Council Australia advises that people with a family history of bowel cancer should speak with their GP about screening options.
Before seeing your GP, try to write down which relatives were affected, their approximate age at diagnosis, and whether they had bowel cancer, bowel polyps or a known inherited bowel cancer condition.
Previous bowel polyps or surveillance colonoscopy
If you have had polyps removed in the past, your doctor may recommend a repeat colonoscopy after a set interval. This is called surveillance colonoscopy. The timing depends on the number, size and type of polyps, whether they were completely removed, and the pathology results.
Some people with low-risk findings may not need another colonoscopy for several years. Others may need closer follow-up if they had multiple polyps, larger polyps, serrated lesions, advanced features, poor bowel preparation or a strong family history.
If you are unsure when your next colonoscopy is due, ask your GP to review your previous colonoscopy and pathology reports. It is better to confirm the recommended interval than to guess or wait until symptoms appear.
Inflammatory bowel disease symptoms or monitoring
Inflammatory bowel disease, or IBD, includes ulcerative colitis and Crohn’s disease. These conditions can cause symptoms such as diarrhoea, rectal bleeding, abdominal pain, urgency, mucus in the stool, fatigue and weight loss.
Colonoscopy may be recommended to help diagnose IBD, assess how much of the bowel is affected, check disease activity, or monitor the bowel over time. People with long-standing IBD may also need surveillance colonoscopy because chronic inflammation can increase bowel cancer risk in some patients.
If you already have IBD and your symptoms change, worsen or do not respond to treatment, speak with your GP or specialist. Do not assume every flare or change is routine.
Do younger adults ever need a colonoscopy?
Bowel cancer is more common in older adults, but younger adults can still develop bowel cancer or other bowel conditions that require investigation. Age alone should not be used to dismiss persistent symptoms.
A younger adult may be referred for colonoscopy if they have rectal bleeding, ongoing bowel habit changes, unexplained iron deficiency anaemia, unexplained weight loss, a strong family history, suspected IBD or a positive bowel screening test arranged by their doctor.
If you are under 45 and have bowel symptoms, the National Bowel Cancer Screening Program may not be the right pathway. Screening tests are designed for people without symptoms. Symptoms should be assessed by a GP, who can decide whether colonoscopy or another test is appropriate.
What can a colonoscopy detect?
A colonoscopy can help detect many bowel conditions. It may find haemorrhoids, diverticular disease, inflammation, ulcers, polyps, narrowing, bleeding, inflammatory bowel disease or bowel cancer. It can also identify normal findings, which can be helpful when symptoms are caused by another condition.
One of the main advantages of colonoscopy is that it can be both diagnostic and therapeutic. This means the specialist can inspect the bowel and, where appropriate, remove polyps or take biopsies during the same procedure.
If tissue samples or polyps are removed, they are usually sent to pathology. Your GP or specialist will explain the results and whether any treatment, follow-up or surveillance colonoscopy is needed.
What happens if your GP refers you?
If your GP recommends colonoscopy, they will usually provide a referral explaining the reason for the procedure. The referral may mention symptoms, test results, family history, previous polyps or other relevant medical history.
Before the procedure, you will need to follow bowel preparation instructions. This usually involves dietary changes, clear fluids and bowel preparation medication. Good preparation is important because the bowel needs to be clean for the specialist to see the lining clearly.
At Direct Endoscopy, patients are given preparation instructions before the procedure. If you take blood-thinning medication, diabetes medication, iron tablets or other regular medicines, ask your GP or the clinic what you should do before the appointment.
Because sedation is commonly used, you will need someone to take you home after the procedure. You should not drive, operate machinery or make important decisions for the rest of the day after sedation.
How Direct Endoscopy can help
If your GP has recommended a colonoscopy because of symptoms, a positive bowel screening test, previous polyps or family history, our team can help you understand the booking process and prepare for the procedure.
At Direct Endoscopy, we support patients who need bowel investigation at several Melbourne locations. During the procedure, the specialist can examine the bowel lining, remove polyps where appropriate, and take biopsies if needed. Your results are then used to guide the next step in your care.
If you already have a referral, you can contact our team to discuss availability, costs, preparation requirements and what to bring on the day. If you are unsure whether colonoscopy is appropriate, speak with your GP first so they can assess your symptoms and risk factors.
Final thoughts
A colonoscopy may be recommended if you have rectal bleeding, persistent bowel habit changes, unexplained abdominal pain, iron deficiency anaemia, unexplained weight loss, a positive bowel screening test, previous polyps or a family history of bowel cancer.
These signs do not automatically mean you have bowel cancer. Many bowel symptoms are caused by less serious conditions. However, persistent or unexplained symptoms should be checked rather than ignored.
If you notice blood in your stool, a lasting change in bowel habits, unexplained weight loss, ongoing abdominal pain, or symptoms that are unusual for you, speak with your GP. If your doctor recommends a colonoscopy, the procedure can help identify the cause and guide the right next step.