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.

New York DOH Approval Status

This test is New York state 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

Paraffin block with less than 25 percent tumor tissue. Specimens fixed in any fixative other than 10 percent neutral buffered formalin. 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.
If multiple specimens (blocks or slides) are sent to ARUP, they must be accompanied by one of the following: an order comment indicating that the ARUP pathologist should choose the specimen most appropriate for testing (e.g., "Choose best block"), or individual orders for each sample submitted. A Pathologist Block Selection Fee (ARUP test code 3002076) will be added to orders that utilize the first option. If multiple specimens are sent to ARUP without a request for pathologist block/slide selection or individual orders, they will be held until clarification is provided.


Ambient: Indefinitely; Refrigerated: Indefinitely; Frozen: Unacceptable


Qualitative Immunohistochemistry (IHC)/Qualitative Real-Time Polymerase Chain Reaction




1-5 days
If reflexed, add 7-10 days.

Reference Interval

Interpretive Data

Refer to report.

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

This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the US Food and Drug Administration. This test was performed in a CLIA certified laboratory and is intended for clinical purposes.

Compliance Category

Modified FDA


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 81210; if further reflexed, add 81288


Component Test Code* Component Chart Name LOINC
0049199 Client Case or Ref # 94736-6
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 31208-2
* 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