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Microsatellite instability (MSI) analysis is a genetic test that evaluates the stability of microsatellite regions in DNA, which are short, repetitive sequences that can vary in length among individuals. This analysis is particularly relevant in the context of hereditary non-polyposis colorectal cancer (HNPCC), commonly known as Lynch syndrome. In individuals with Lynch syndrome, there is a defect in the DNA mismatch repair (MMR) system, leading to an accumulation of errors in the DNA sequence. When these errors occur, the microsatellites can become unstable, resulting in variations in their length. The presence of MSI is indicative of a potential MMR gene mutation, which is a hallmark of Lynch syndrome. The analysis involves comparing neoplastic (tumor) tissue to normal tissue to assess the degree of instability. Specifically, the test examines several microsatellite markers, including BAT25 and BAT26, to determine whether the tumor exhibits high instability (unstable high) or low instability (unstable low). A tumor is classified as unstable high if two or more microsatellite regions show changes, while unstable low indicates that only one region is affected. Conversely, if there are no changes between the tumor DNA and the normal DNA, the tumor is considered microsatellite stable (MSS). The identification of high MSI can suggest the presence of Lynch syndrome, prompting further genetic testing and evaluation. This analysis is crucial as it not only aids in the diagnosis of hereditary cancer syndromes but also has implications for treatment decisions, as tumors with MSI may respond differently to certain chemotherapeutic agents compared to those that are MSS. Routine MSI testing is recommended for individuals diagnosed with colorectal cancer and certain other malignancies to guide clinical management and familial risk assessment.
© Copyright 2025 Coding Ahead. All rights reserved.
Microsatellite instability analysis is indicated for the following conditions:
The procedure for microsatellite instability analysis involves several key steps to ensure accurate results:
After the microsatellite instability analysis is completed, the results are typically reviewed by a healthcare professional, who will discuss the findings with the patient. If high instability is detected, further genetic testing may be recommended to confirm the presence of Lynch syndrome or other hereditary conditions. Additionally, the results can influence treatment options, as tumors with high MSI may respond differently to certain chemotherapeutic agents. Patients may also be referred for genetic counseling to discuss the implications of the findings for themselves and their family members. Regular follow-up and monitoring may be advised based on the results and the patient's overall health status.
| Short Descr | MICROSATELLITE INSTABILITY | Medium Descr | MICROSATELLITE INSTAB ANAL MISMATCH REPAIR DEF | Long Descr | Microsatellite instability analysis (eg, hereditary non-polyposis colorectal cancer, Lynch syndrome) of markers for mismatch repair deficiency (eg, BAT25, BAT26), includes comparison of neoplastic and normal tissue, if performed | Status Code | Statutory Exclusion (from MPFS, may be paid under other methodologies) | Global Days | XXX - Global Concept Does Not Apply | PC/TC Indicator (26, TC) | 9 - Not Applicable | Multiple Procedures (51) | 9 - Concept does not apply. | Bilateral Surgery (50) | 9 - Concept does not apply. | Physician Supervisions | 09 - Concept does not apply. | Assistant Surgeon (80, 82) | 9 - Concept does not apply. | Co-Surgeons (62) | 9 - Concept does not apply. | Team Surgery (66) | 9 - Concept does not apply. | Diagnostic Imaging Family | 99 - Concept Does Not Apply | CLIA Waived (QW) | No | APC Status Indicator | Service Paid under Fee Schedule or Payment System other than OPPS | Type of Service (TOS) | 5 - Diagnostic Laboratory | Berenson-Eggers TOS (BETOS) | T1H - Lab tests - other (non-Medicare fee schedule) | MUE | 1 | CCS Clinical Classification | 234 - Pathology |
| 90 | Reference (outside) laboratory: when laboratory procedures are performed by a party other than the treating or reporting physician or other qualified health care professional, the procedure may be identified by adding modifier 90 to the usual procedure number. | 59 | Distinct procedural service: under certain circumstances, it may be necessary to indicate that a procedure or service was distinct or independent from other non-e/m services performed on the same day. modifier 59 is used to identify procedures/services, other than e/m services, that are not normally reported together, but are appropriate under the circumstances. documentation must support a different session, different procedure or surgery, different site or organ system, separate incision/excision, separate lesion, or separate injury (or area of injury in extensive injuries) not ordinarily encountered or performed on the same day by the same individual. however, when another already established modifier is appropriate it should be used rather than modifier 59. only if no more descriptive modifier is available, and the use of modifier 59 best explains the circumstances, should modifier 59 be used. note: modifier 59 should not be appended to an e/m service. to report a separate and distinct e/m service with a non-e/m service performed on the same date, see modifier 25. | XU | Unusual non-overlapping service, the use of a service that is distinct because it does not overlap usual components of the main service | 26 | Professional component: certain procedures are a combination of a physician or other qualified health care professional component and a technical component. when the physician or other qualified health care professional component is reported separately, the service may be identified by adding modifier 26 to the usual procedure number. | GA | Waiver of liability statement issued as required by payer policy, individual case | GV | Attending physician not employed or paid under arrangement by the patient's hospice provider | GZ | Item or service expected to be denied as not reasonable and necessary |
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| 2012-01-01 | Added | Added |
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