Don't trust fecal occult blood test too much

Fecal occult blood test is simple, convenient and cheap, and is one of the most commonly used tests for diagnosing colorectal cancer. However, this test still has a considerable number of missed cases, so patients should not only trust this test method, but also do more tests to confirm the disease.

Can routine stool tests detect colorectal cancer? Regular fecal occult blood tests are performed for initial screening, and colonoscopy is performed for those who are positive. This is a common method for early detection of colorectal cancer. However, fecal occult blood tests can produce false positive results, such as hemorrhoids and gastric ulcers, but their specificity is not very strong. If a fecal occult blood test is positive, a colonoscopy is required to confirm whether there is a colon tumor. "

If fecal occult blood continues to be positive, you should be alert to gastric cancer

Black stool or positive occult blood in stool often indicates the presence of gastrointestinal bleeding, and gastric cancer can also cause bleeding, which is due to the growth characteristics of gastric cancer. Gastric cancer grows very fast, and rapid growth requires sufficient nutrition to meet, so the blood supply is much higher than usual, and often insufficient blood supply will lead to cell necrosis, ulcers and bleeding, and medical treatment has no significant effect on cancerous ulcers or erosions, so the fecal occult blood test continues to be positive.

Gastric cancer bleeding can be divided into three types: small, moderate and large. The tumor wound oozes blood, the amount of blood in the stool is not much, and the color does not change. However, the test result may be positive. If the daily bleeding volume is more than 50ml, black stool may appear.

However, not all causes of black stool or positive occult blood in stool are gastric cancer. Any part of the body from the mouth to the anus can cause gastrointestinal bleeding as long as there is mucosal damage, which will manifest as black stool or occult blood in stool. Therefore, if black stool or positive occult blood in stool is found, the cause of bleeding must be found out, especially for people over 40 years old. Once it is found, it is necessary to go to the hospital for diagnosis and treatment in time.

If the condition worsens, when the cancer invades larger blood vessels and the blood vessels rupture, causing more bleeding, it will cause vomiting of blood. The vomited blood is coffee-colored due to the effect of stomach acid, and the vomitus is also coffee-like liquid. Therefore, when there is black bloody stool or occult blood in the stool is continuously positive, be alert to the occurrence of gastric cancer.

False positive results are more common, and a positive result does not necessarily mean that bowel cancer is present, because blood in the stool can have many causes other than benign or malignant tumors. Hemorrhoids are the most common cause, but others include diverticular disease, inflammatory bowel disease, and even eating foods that are not conducive to this test, such as red meat or aspirin.

The only reason for a false negative result is if the colorectal cancer does not bleed during the test period, which is very rare. Some rectal cancers bleed only intermittently or not at all. Larger polyps and polyps on the right side of the colon are more likely to bleed, which is easy to detect with this test.

The statistics on the false positive and false negative rates of fecal occult blood tests are staggering. One study found that approximately 40% to 50% of patients with positive fecal occult blood tests actually had adenomatous polyps of the large intestine, of which 12% were cancers and the rest were benign tumors. Another study showed that only 5% to 10% of patients with positive fecal occult blood tests were confirmed to have malignancies. Moreover, the discriminability of positive fecal occult blood tests to indicate the presence of cancer or polyps is even worse in younger patients.

A false positive means that the patient needs to undergo further examination, which is expensive and causes a lot of inconvenience to the patient; a false negative has more serious consequences, making the patient think that he or she does not have cancer and give up further examination and treatment, or even ignore other symptoms and danger signs.

In short, patients do not need to panic when the test results are positive, and do not completely trust it when the test results are negative. Do more other tests to confirm the disease to avoid misdiagnosis, missed diagnosis, and delayed treatment.