Blood test reliability
The septin 9 blood test is the only blood test approved by the U.S. Food and Drug Administration for CRC screening and is indicated for those who have declined first-line tests. However, the extent of usage of the blood test in this context is unclear, as it has only been approved since 2016.
Because the blood test is not covered by Medicare, Dr. Liang said, accessibility has been limited. One of the reasons for the lack of coverage is that the blood tests are less reliable than first-line tests, he said.
The test detects methylated septin 9 DNA, a biomarker for CRC. The FDA-approved version of the test has a sensitivity of 68% and a specificity of 79% for CRC.
Dr. May said she’d have more confidence in the blood tests if those numbers were higher, at 80%-90%.
Dr. Liang told this news organization that previous research has compared test use when colonoscopy, FIT, and a blood test are considered equally, but because the blood test is indicated only after a person declines first-line screening, his team designed an approach in which the blood test was a second-line option for its target population.
Other blood tests now on the market or under development appear to have higher sensitivity and specificity, he added.
“We think our results are actually applicable to a blood test in general,” Dr. Liang said.
Blood tests are only the first step, though. Getting people who screen positive to follow up with a diagnostic colonoscopy is critical, Dr. May and the authors agree.
“That’s something we, as a nation, just haven’t figured out,” Dr. May said. “It has to become a priority.”
The study was supported in part by the Veterans Health Administration and was funded by Epigenomics and a grant from the New York Society for Gastrointestinal Endoscopy’s Florence Lefcourt Endoscopy Research Award to Dr. Laing, who is also supported by the National Cancer Institute. Dr. Liang has received research support from Epigenomics and Freenome and is on the advisory board for Guardant Health. The remaining authors disclosed no relevant financial relationships. Dr. May is a consultant for Exact Sciences and Geneoscopy, both of which are developing stool tests, and for Freenome, which is developing stool and blood tests.
A version of this article originally appeared on Medscape.com.