Stool vs. Blood Tests For Colon Cancer Diagnosis

Stool vs. Blood Tests For Colon Cancer Diagnosis

The most well-known and physician-recommended screening test for colon cancer is a colonoscopy. It is most often preferred over other screening tests because of the ability for the practicing physician to be able to detect and remove polyps during the procedure. However, the number of eligible adults who are not getting screened for cancer has prompted many physicians to offer options to their patients along with a colonoscopy. Stool-based kits are often prescribed to patients who are hesitant to get a colonoscopy and are at a low to average risk for colon cancer. These tests are done at home and do not require the complicated bowel cleansing or any form of sedation to screen for colon cancer. At home stool tests ask for a small sample of stool that is then analyzed in a lab for evidence of blood that may indicate the presence of a precancerous polyp or colon cancer.

Another new approach to colorectal cancer screening is the use of blood tests that detect the presence of cellular markers in the bloodstream. Polyps and tumors in the colon shed cells that are absorbed into the bloodstream. These cells are called circulating tumor cells (CTCs) and are made up of epithelial cells that are associated with colorectal tumors and adenomas.

Research scientists have developed a special blood test that uses antibodies to detect these cancerous cells. These blood tests have been shown to be highly sensitive and specific for detecting colorectal cancer, but unfortunately miss the detection of polyps.

Research scientists have developed a special test that uses antibodies to detect these cells. These blood tests have been shown to be highly sensitive and specific for detecting colorectal cancer, but unfortunately miss the detection of polyps. In this article, we will address the pros and cons of stool tests and blood tests to help increase your awareness of the benefits of each test in screening for colorectal cancer. 

At Home Colon Cancer Stool Tests

There are currently three stool tests that are approved for colorectal cancer screening in the United States. These include:

Fecal immunochemical test (FIT).  This test uses antibodies that specifically react with a blood protein in the stool. Physicians typically order the test to be repeated annually. 

Guaiac-based fecal occult blood test (gFOBT). Conducted yearly, the gFOBT uses a chemical (guiac) to detect microscopic amounts of blood in the stool. 

Stool DNA test (also known as FIT-DNA test). The most current stool test combines the FIT test with a test that can detect abnormally mutated DNA in the stool. Unlike the FIT and gFOBT, a stool DNA test can be repeated every three years if no abnormalities are found. 

People frequently prefer these tests over colonoscopies because the test is done in the comfort of your own home and is noninvasive and requires no bowel preparation.

Pros and Cons Home-based Stool Tests

Pros

• Detects hidden blood to identify the presence of abnormal tissue, polyps, or colorectal cancer
• Noninvasive and requires no sedation or anesthesia
• No bowel preparation needed
• Test is done at home requiring a simple stool collection
• High specificity and high sensitivity for detecting polyps and colorectal cancer

Cons

• You will need additional tests if blood is found, including a colonoscopy
• The test may fail to detect small polyps and cancer
• May require restricted diet and avoiding medications a few days before stool sample collection
• Does not examine the entire colon
• A colonoscopy is required If there are polyps found 
• Tests need to be done every year
• You have to handle your stool sample

Blood Test For Colorectal Cancer

Colorectal cancer cells are detected with blood tests using genetic or tumor biomarkers. If these biomarkers are detected in a blood test, then it only suggests that a person may have colon cancer.

Colorectal cancer cells are detected with blood tests using genetic or tumor biomarkers. If these biomarkers are detected in a blood test, then it only suggests that a person may have colon cancer.

These tests, like stool-based tests, do not diagnose colorectal cancer. Rather, both stool-based and blood tests detect signs of colon cancer in the form of hidden blood or tumor markers respectively. There are two main types of colorectal cancer blood tests, these include:

Tumor marker tests. Unlike FDA-approved screening stool tests such as FIT, FOBT, or Cologuard™,  tumor marker blood tests that detect colon cancer tumor markers are typically used to monitor patients who already have been diagnosed with colorectal cancer. The most common tumor biomarkers for colorectal cancer is called carcinoembryonic antigen (CEA) and CA 19-9. These tests help to determine if cancer treatment is working and sometimes to determine how likely it is that the disease will recur. 

DNA-based blood test. These tests detect mutated cells shed by colon cancer tumors that are found in the blood. They typically are looking for a specific biomarker (such as Septin 9) that is distinct from normal cells and is shed by colorectal cancer tumors. 

Pros and Cons Blood Tests

Pros

• High sensitivity and specificity (86%) for all stages of colorectal cancer
• High sensitivity (79%) for adenomatous lesions whereas stool-based tests have a low sensitivity
• Requires no preparation 
• Patients do not need to restrict their diet or medications
• Noninvasive excepting the blood draw
• Patients are more likely to complete screening when compared to a colonoscopy

Cons

• Positive test requires a follow-up colonoscopy that may not be covered by insurance
• Research has not shown any effects on morbidity or mortality rates of colorectal cancer
• False negative may cause a person with undetected colorectal cancer or polyps to delay cancer diagnosis due to false reassurance
• Lower specificity than FIT and Cologuard stool tests (false positives lead to unnecessary colonoscopies)
• Limited sensitivity for early stage colorectal cancer and polyps detection

Blood Test Providers

Be Screened™-CRC

• Blood-based test intended for people between the ages of 50 and 85
• Available without a prescription through Sonora Quest Laboratories
• Tests three cancer related proteins 
• No dietary or medication restrictions

Epi proColon®

• The only FDA-approved blood test for colorectal cancer
•  Nor dietary or medication restrictions
• Has a similar cancer detection rate as a fecal immunochemical test (FIT)
• Sensitivity for CRC is 62-71% and specificity is 91-92%
• Detects methylated Septin 9 DNA, a biomarker associated with colorectal cancer

FirstSightCRC

• Test is not yet available on the market
• Detects precancerous cells in the blood from polyps
• 90% specificity and 100% sensitivity for detecting colorectal cancer
• 75.5% sensitivity for detecting advanced adenomas
• Tests three different biomarkers, including epithelial cells and mutated DNA markers

Costs

Blood Tests

Be Screened™ CRC

$170

EpiPro 

Prescription only

Medicare and Medicaid cost – $192

Stool Tests

EZ Detect

$8

Everlywell FIT

$49

Cologuard

$599