81245

FLT3 (fms-like tyrosine kinase 3) Gene Analysis; Internal Tandem Duplication (ITD) Variants

CPT 81245 describes the molecular genetic laboratory analysis of the FLT3 (fms-like tyrosine kinase 3) gene, specifically targeting internal tandem duplication (ITD) variants. The FLT3 gene encodes a class III receptor tyrosine kinase that plays a critical role in the proliferation, survival, and differentiation of hematopoietic progenitor cells. Mutations in this gene are among the most frequent genetic alterations in acute myeloid leukemia (AML), occurring in approximately 25% to 30% of adult patients. The internal tandem duplication (ITD) variant involves the head-to-tail duplication of a DNA sequence within the juxtamembrane domain, typically involving exons 14 and 15. This mutation leads to the constitutive activation of the kinase, triggering downstream signaling pathways independent of ligand binding, which results in uncontrolled cellular growth. Clinically, the presence of an FLT3-ITD mutation is recognized as a significant negative prognostic indicator, often associated with high leukocytic counts, an increased risk of relapse, and decreased overall survival. The laboratory procedure typically utilizes polymerase chain reaction (PCR) amplification followed by fragment analysis (capillary electrophoresis) of DNA extracted from peripheral blood or bone marrow. The results identify the presence of the duplication and can provide an allelic ratio (mutant to wild-type), which is essential for risk stratification and determining eligibility for targeted therapies, such as FLT3 inhibitors like midostaurin or gilteritinib.

Clinical Indications

  • Initial diagnostic workup for patients with suspected or confirmed Acute Myeloid Leukemia (AML).
  • Prognostic risk stratification of AML patients to determine intensive vs. non-intensive treatment pathways.
  • Identification of patients eligible for targeted therapy with FLT3 inhibitors.
  • Evaluation of patients with Acute Promyelocytic Leukemia (APL).
  • Assessment of disease progression or relapse in patients with previously diagnosed myeloid malignancies.
  • Monitoring of minimal residual disease (MRD) in FLT3-ITD positive patients post-treatment.
  • Evaluation of patients with myelodysplastic syndromes (MDS) transitioning to AML.

Procedure Steps

  1. Specimen Collection: Procurement of 3-5 mL of peripheral blood in EDTA (lavender top) or 1-2 mL of bone marrow aspirate.
  2. DNA Extraction: Isolation and purification of genomic DNA from the nucleated cells of the blood or marrow specimen.
  3. PCR Amplification: Targeted amplification of FLT3 exons 14 and 15 using specific primers designed to flank the juxtamembrane domain.
  4. Fragment Analysis: Separation of PCR products via capillary electrophoresis to detect size differences between wild-type and mutated (duplicated) alleles.
  5. Allelic Ratio Calculation: Quantitative comparison of the area under the curve for the mutant peak versus the wild-type peak.
  6. Data Interpretation: Analysis of electropherograms by a molecular pathologist or qualified laboratory scientist.
  7. Reporting: Final clinical report generation including mutation status, allelic ratio, and clinical significance.

Coding Guidelines

  • 81245 is a Tier 1 molecular pathology code specific to the ITD variant of the FLT3 gene.
  • If the laboratory also analyzes the tyrosine kinase domain (TKD) variants (e.g., D835, I836), CPT 81246 should be reported in addition to 81245.
  • Do not report 81245 in conjunction with genomic sequence analysis panels (e.g., 81450, 81455) if the FLT3-ITD status is already included in that panel analysis.
  • The code represents the technical and professional components of the molecular analysis; if the interpretation is performed by a physician in a separate facility, modifier 26 may be applicable depending on the setting.
  • Ensure the medical record documentation reflects the morphology and suspected diagnosis of AML or related myeloid neoplasms.

Associated ICD-10 Codes