Ordering Recommendation

Preferred screening test for Lynch syndrome (LS) in individuals with colorectal cancer. Definitive diagnosis of LS requires additional targeted germline mismatch repair gene testing. Do not use in endometrial cancer.


Qualitative Immunohistochemistry/Qualitative Real-time Polymerase Chain Reaction




Within 5 days. Within 15 days if reflexed.

New York DOH Approval Status
This test is New York DOH approved.
Specimen Required
Patient Preparation

Tumor tissue.

Specimen Preparation

Tumor Tissue: Formalin fix (10 percent neutral buffered formalin is preferred) and paraffin embed tissue. If sending precut slides, do not oven bake. Transport tissue block or 15 unstained (3- to 5-micron thick sections), positively charged slides in a tissue transport kit (ARUP Supply #47808). Available online through eSupply using ARUP Connect™ or contact ARUP Client Services at (800) 522-2787. (Min: 10 slides). Protect paraffin block and/or slides from excessive heat.

Storage/Transport Temperature

Room temperature. Also acceptable: Refrigerated. Ship in cooled container during summer months.

Unacceptable Conditions

Less than 25 percent tumor. Specimens fixed/processed in alternative fixatives (alcohol, Prefer). Decalcified specimens.


Include surgical pathology report. Submit electronic request. If you do not have electronic ordering capability, use an ARUP requisition form complete with an ARUP client number. For additional technical details, please contact ARUP Client Services at (800) 522-2787.


Ambient: Indefinitely; Refrigerated: Indefinitely; Frozen: Unacceptable

Reference Interval
Interpretive Data

Refer to report.

Refer to the Colorectal Cancer or Lynch Syndrome topic at arupconsult.com.

Compliance Category



If MLH1 is abnormal for Mismatch Repair by IHC, then BRAF codon 600 will be added. If BRAF codon 600 is negative, MLH1 Promoter Methylation will be added. Additional charges apply.

Hotline History
CPT Codes

88342; 88341 x3; if reflexed, add 88381, 81210; if further reflexed, add 81288

Component Test Code* Component Chart Name LOINC
0049199 Client Case or Ref # 49581-2
0049303 Mismatch Repair by IHC, Result 50595-8
0049305 Mismatch Repair by IHC with MLH1 50322-7
0049310 Mismatch Repair by IHC with MSH2 50323-5
0049320 Mismatch Repair by IHC with MSH6 50324-3
0049325 Mismatch Repair by IHC with PMS2 50328-4
3002969 MSI Tissue Source
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
  • MSI
  • MSI reflex to BRAF and MLH1 Methylation
  • MSI with BRAF, MLH1reflex
Mismatch Repair by Immunohistochemistry with Reflex to BRAF Codon 600 Mutation and MLH1 Promoter Methylation