How is a Fluorescence In Situ Hybridization (FISH) panel ordered?

How to Order a FISH Panel

A FISH (Fluorescence In Situ Hybridization) panel is ordered through a laboratory requisition form that specifies the appropriate probe set for the clinical indication, along with proper specimen collection and handling requirements. 1

Ordering Process

Step 1: Determine Clinical Indication

• Identify the specific clinical question (e.g., suspected chromosomal deletion, translocation, or gene rearrangement)
• Common indications include:
  • Hematological malignancies (leukemia, multiple myeloma) 1
  • Solid tumors requiring specific genetic markers 1
  • Constitutional cytogenetic abnormalities 1
  • Prenatal diagnosis of chromosomal anomalies 1

Step 2: Select Appropriate FISH Panel

• Choose a panel based on clinical suspicion:
  • Disease-specific panels (e.g., CLL panel with probes for 11q22.3, 13q14, chromosome 12 centromere, 17p13.1) 2
  • Multiple myeloma panel (e.g., 14q32, t(11;14), 13q14, 17p13.1) 1
  • Targeted single-gene probes for specific abnormalities 1

Step 3: Complete Laboratory Requisition

• Include essential information:
  • Patient demographics
  • Clinical indication/suspected diagnosis
  • Specific FISH panel requested
  • Relevant clinical history
  • Physician contact information 1

Step 4: Specimen Collection

• Collect appropriate specimen type:
  • Peripheral blood (heparin tube, not EDTA)
  • Bone marrow aspirate
  • Fresh tissue
  • Paraffin-embedded tissue sections (3-6 μm) 1
  • Amniotic fluid or chorionic villus sample (for prenatal testing) 1

Step 5: Specimen Handling

• Follow specific handling requirements:
  • Maintain specimen at room temperature
  • Transport promptly to laboratory
  • For paraffin sections, ensure proper fixation and processing
  • For bone marrow/blood, use sodium heparin anticoagulant 1

Important Considerations

Specimen Quality Requirements

• For hematologic malignancies, CD138+ cell enrichment may be required 1
• For paraffin-embedded tissues, pathologist review of target area is recommended 1
• Minimum cell count requirements vary by test type

Interpretation Guidelines

• Analysis requirements:
  • Minimum of 100 interphase nuclei for diagnostic samples
  • Minimum of 200 interphase nuclei for follow-up studies 1
  • For metaphase FISH, at least 20 metaphases should be analyzed 1

Common Pitfalls to Avoid

• Inadequate specimen collection or improper anticoagulant
• Failure to specify the appropriate probe set
• Insufficient clinical information to guide testing
• Delayed transport affecting cell viability
• Failure to recognize that FISH cannot detect all genetic abnormalities (e.g., point mutations) 1

Validation Requirements

• Laboratories must validate each FISH probe before clinical use
• Validation includes establishing:
  • Probe sensitivity and specificity
  • Normal cutoff values
  • Appropriate control samples 3

FISH testing is particularly valuable when conventional cytogenetics yields normal results, as it can detect clinically significant abnormalities with higher sensitivity, making it the preferred testing methodology for many hematologic disorders 2.