Appendix

Note 1: The microsatellite instability (MSI) test is a genetic test performed on tumor tissue to look for differences in length of certain non-functioning sections of DNA. The differences are caused by problems with the genes that normally repair DNA. A high-positive MSI (MSI-H) result may indicate that the gene repair problem is related to the development of the cancer, and that the patient may have hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome.) A low-positive or stable MSI result (stable meaning that there are no differences in the lengths) means it is unlikely that the cancer is related to a hereditary condition.
Note 2: Testing for MSI may be done by immunology or genetic testing. Some laboratories only test for MSI via immunology. Results from immunology will only provide you with positive or negative results and will not specify whether the MSI is low or high. If the testing was done via immunology, do not use codes 040 or 050. Only genetic testing results will specify whether the MSI is low or high.

Code	Description
020	Microsatellite instability (MSI) stable; no MSI; negative, NOS
040	MSI unstable low; positive, low
050	MSI unstable high; positive, high
060	MSI unstable, NOS; positive, NOS
988	Not applicable: Information not collected for this case (If this information is required by your standard setter, use of code 988 may result in an edit error.)
997	Test ordered, results not in chart
998	Test not done (test not ordered and not performed)
999	Unknown or no information Not documented in patient record

CS Site-Specific Factor 7Microsatellite Instability (MSI)