PT Health Watch: How laboratory tests can help detect colorectal cancer early

Colorectal cancer, which affects the colon and rectum, is one of the most common cancers globally, yet it can remain unnoticed for a long time because some people have no symptoms in the early stages.

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The World Health Organisation (WHO) estimates that 1.9 million new cases of colorectal cancer and more than 900,000 deaths occurred globally in 2022.

The agency said symptoms, when they occur, may include blood in the stool, persistent changes in bowel habits, abdominal pain, unexplained weight loss and fatigue.

Because some people may not notice any warning signs, screening can provide an opportunity to identify possible abnormalities before the disease becomes advanced.

What happens before a diagnosis is confirmed?

Laboratory investigations are an important part of that process, as medical laboratory scientists examine samples that can provide clues about what is happening in a patient’s body.

Speaking with PT HEALTH WATCH, Adedoye David, a medical laboratory scientist, said laboratory testing contributes to the investigation of colorectal cancer through the examination of biological samples, including stool, blood and tissue.

One of the investigations is the Faecal Occult Blood Test (FOBT), which detects blood in stool that may not be visible to the naked eye.

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Another is the Faecal Immunochemical Test (FIT), which uses antibodies to detect human haemoglobin in stool.

These tests can help identify people who may require further assessment, but Mr David stressed that detecting blood in stool is not the same as diagnosing cancer.

“Stool-based tests are very important for detecting hidden blood in stool. It could be reliable if the test investigation is carried out using the right and standard operating procedures.

“But as much as it can be reliable in detecting hidden blood, it might not be totally reliable in the diagnosis of colorectal cancer,”he said.

Where further investigation is necessary, Mr David said a patient may be referred for procedures such as colonoscopy, during which abnormal areas can be identified and tissue samples taken for laboratory examination.

A biopsy can then help determine whether the abnormal tissue is cancerous.

Why symptoms should not be ignored

The distinction between screening and diagnosis is important because colorectal cancer does not always announce itself with obvious symptoms.

A person who feels healthy may therefore not consider testing necessary, while another may receive a negative stool test and conclude that further medical attention is unnecessary.

Mr David said both assumptions could be misleading.

He urged people to seek medical advice when they experience persistent symptoms rather than waiting for them to become severe.

He also advised people with a family history of colorectal cancer or long-term inflammatory bowel disease to discuss their risk with healthcare professionals and determine whether they require earlier or more frequent screening.

WHO identifies family history of colorectal cancer and certain inflammatory bowel diseases among factors that can increase a person’s risk of developing the disease.

Although colorectal cancer is more common with increasing age, it is not exclusively a disease of older people. WHO has also reported a rising incidence among younger adults in several countries.

Screening is only useful when people can complete it

The challenge, however, is not simply persuading people to undergo screening. The health system must also be able to support them when a test produces an abnormal result.

Evidence from Nigeria illustrates this point.

A Nigerian community-based study involving more than 2,000 adults found that FIT screening was feasible. However, the researchers also highlighted challenges with follow-up colonoscopy after positive results.

This means that detecting a possible problem is only one part of the process. Patients must be able to access the additional investigations required to establish what the abnormal result means and, where necessary, begin treatment.

Mr David identified limited facilities capable of carrying out some key investigations and the cost of available services as major challenges facing colorectal cancer testing in Nigeria.

For people who may already be hesitant about testing, the cost and availability of diagnostic services can make early detection even more difficult.

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Mr David also urged Nigerians to overcome the embarrassment that may come with providing stool samples for laboratory examination.

“There is nothing to be ashamed of producing a stool sample. It is just like any other medical sample and it is needed for us to carry out informed diagnosis,” he said.

Ultimately, a stool test is not a verdict on whether a person has cancer. Rather, it can be one step in a process that helps health professionals decide who may need further investigation.

For Mr David, improving colorectal cancer outcomes therefore requires both public awareness and access to appropriate laboratory and diagnostic services, so that people can seek help early and abnormal findings can be properly investigated.