FISH Testing: Specimen Source
FISH (fluorescence in situ hybridization) can be performed on both peripheral blood and bone marrow specimens, with bone marrow being the preferred specimen for most hematologic malignancies, though peripheral blood is acceptable when it contains sufficient neoplastic cells.
Specimen Selection Based on Clinical Context
The choice between peripheral blood and bone marrow for FISH testing depends on the specific disease and clinical scenario:
Bone Marrow is Preferred For:
- Acute leukemias - Bone marrow is the preferred specimen, but peripheral blood can be used when circulating neoplastic cells exceed the analytical sensitivity of the assay 1
- Myelodysplastic syndromes (MDS) - Bone marrow aspirate is preferred 1
- Plasma cell neoplasms - Bone marrow specimen is required, with CD138+ enriched samples strongly recommended 1
- Most hematologic malignancies - Bone marrow aspirate is the preferred specimen 1
Peripheral Blood is Acceptable For:
- Chronic myeloid leukemia (CML) - Either bone marrow or peripheral blood is adequate to establish diagnosis, though bone marrow is recommended at diagnosis to assess for disease progression 1
- Myeloproliferative neoplasms (MPNs) - Peripheral blood may be used if there is peripheral involvement 1
- Any condition with sufficient circulating neoplastic cells - Peripheral blood yields informative results when it contains sufficient neoplastic cells that exceed the analytical sensitivity of the assay 1
Alternative Specimen Sources
When standard specimens are inadequate, FISH can be performed on:
- Bone marrow smears or core biopsy touch imprint preparations - Used for interphase FISH analysis when inadequate bone marrow aspirate is obtained 1
- Bone marrow core biopsy sections - An option in cases with a dry tap, requiring special processing 1
- Lymph node biopsies - Appropriate for lymphoid malignancies 1
Important Technical Considerations
The correlation between peripheral blood FISH and bone marrow cytogenetics varies by treatment context. Research shows that in CML patients treated with imatinib, FISH on unselected peripheral blood white cells correlates poorly with bone marrow cytogenetics, while FISH on peripheral blood neutrophils shows much better correlation 2. This highlights that the specimen type matters and may need to be adjusted based on the clinical scenario.
Common Pitfall
Do not assume peripheral blood FISH is always equivalent to bone marrow FISH. The proportion of neoplastic cells differs between tissues - for example, in B-cell chronic lymphocytic leukemia with trisomy 12, lymph nodes show significantly higher proportions of trisomic cells than peripheral blood or bone marrow 3. This tissue-specific distribution can affect test sensitivity and interpretation.
Bottom Line
FISH is not exclusively a blood test or a bone marrow test - it's a laboratory technique that can be applied to multiple specimen types. The optimal specimen depends on where the neoplastic cells are most concentrated and accessible for the specific disease being evaluated 1.