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Stool DNA FIT

Cologuard is a multitarget stool DNA and fecal immunochemical test (s-DNA-FIT) that detects both hemoglobin and gene mutations associated with colorectal cancer. The U.S. Food and Drug Administration has approved s-DNA-FIT (Cologuard, Exact Sciences) as a screening test for colorectal cancer (CRC) screening in asymptomatic persons at average risk of CRC beginning at age 45 years.

s-DNA-FIT includes FIT along with detection of DNA biomarkers for cancer, such as mutant KRAS, aberrant methylation of BMP3, and NDGR4, in cells that are shed into the stool from the lining of the colon and rectum. s-DNA-FIT is reported as positive if either the FIT or DNA biomarker component is abnormal.

The sensitivity and specificity of s-DNA-FIT compared to other stool-based screening tests for CRC are shown in the following table. 

Performance

hs gFOBT

FIT

s-DNA-FIT

Sensitivity

0.75

0.74

0.93

Specificity

0.97

0.94

0.84

 

S-DNA-FIT is more sensitive than high sensitivity guaiac FOBT and FIT but is less specific. Lower specificity means that more people are referred for unnecessary follow-up colonoscopies. Studies have shown that 45% of patients with a positive s-DNA-FIT result have no significant findings on colonoscopy.However, the less invasive nature of s-DNA-FIT may mean that more people might be willing to be screened for colorectal cancer. 

Cologuard costs $599 compared to $25 for FIT. Medicare covers the new test once every three years for Medicare beneficiaries who meet all of the following criteria:

  • age 50 to 85 years,
  • asymptomatic and
  • average risk of developing colorectal cancer 

According to the 2022 Medicare fee schedule, reimbursement for high-sensitivity gFOBT was $4.38, for FIT was $18.05, and for s-DNA-FIT was $509.

s-DNA-FIT requires a prescription, and the kit is mailed directly to the patient. A full stool sample needs to be collected in a bucket that contains a buffer for DNA stability, and a small stool sample is provided for the FIT component of the test.

Patients with positive test results are advised to undergo a diagnostic colonoscopy.

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