What are other Names for this Test? (Equivalent Terms)

• FISH (Fluorescence in situ Hybridization)

What is Fluorescence in situ Hybridization? (Background Information)

• Fluorescence in situ Hybridization (FISH) is a specialized genetic testing technique that is used to detect chromosomal abnormalities that are too tiny to be detected using conventional microscopic studies
• Fluorescence in situ Hybridization generally looks at one specific area of a chromosome. This technique uses a small chemical that glows brightly when the specific chromosomal region is detected. When an individual has a deletion in their chromosome, only one bright spot can be seen compared to two. Similarly, duplications cause three bright spots to appear
• FISH works by inserting small fluorescent DNA strands known as probes to “complement” specific parts of a chromosome. When DNA is heated, the two DNA strands break apart and the probe is able to insert itself. If a small deletion is present in the complementary region of the probe, the probe will not hybridize properly. If a duplication is present, more of the probe will hybridize
• The DNA in the cells is double-stranded. Each strand contains a mixture of four bases, namely A, T, C, and G. The bases of each strand bind with each other to hold the DNA together. The DNA is only able to bind if the bases on the two strands are complementary to each other
• Fluorescence in situ Hybridization is able to detect many small deletions, duplications, and rearrangements that cannot be seen through standard microscopic analyses. The results from a FISH analysis may help prevent individuals from having to undergo multiple other tests

Note: Molecular testing has limitations due to the molecular method and genetic mutational abnormalities being tested. This can affect the results on a case-by-case basis. Consultation with your healthcare provider will help in determining the right test and right molecular method, based on individual circumstances.

What are the Clinical Indications for performing the Fluorescence in situ Hybridization?

Following are the clinical indicators for performing the Fluorescence in situ Hybridization test: 

• If the signs and symptoms of a specific (known) chromosomal disorder is suspected
• To assist (and in some cases, confirm) the initial diagnosis
• If there is a family history of the medical disorder/condition
• To distinguish other conditions that have similar features (signs and symptoms)
• To help in determining treatment options

How is the Specimen Collected for the Fluorescence in situ Hybridization?

Following specimen(s) may be collected for Fluorescence in situ Hybridization test:

• Blood
• Amniotic fluid following an amniocentesis
• Samples of placenta from chorionic villus sampling (CVS)

The specimen sample requirements may vary from lab to lab. Hence, it is important to contact the testing lab for exact specimen requirements, before initiating the testing process.

• Process of obtaining the sample: As outlined by the laboratory testing facility
• Preparation required: As outlined by the laboratory testing facility

Cost of Fluorescence in situ Hybridization:

• The cost of the test procedure depends on a variety of factors, such as the type of your health insurance, annual deductibles, co-pay requirements, out-of-network and in-network of your healthcare providers and healthcare facilities
• In many cases, an estimate may be provided before the test is conducted. The final amount may depend upon the findings during the test procedure and post-operative care that is necessary (if any)

What is the Significance of the Fluorescence in situ Hybridization Result?

The results of the Fluorescence in situ Hybridization (FISH) may indicate if any of the following chromosomal anomaly has taken place:

• Deletion/microdeletion
• Duplication/microduplication
• Number and types of genes involved (such as deleted/duplicated)

Advantages of FISH: 

• It is useful in detecting many small deletions, duplications, and rearrangements that cannot be seen through standard microscopic analyses
• The results from a FISH analysis may help prevent individuals from having to undergo multiple other tests

Limitations of FISH: 

• FISH testing does not screen all the chromosomes of an individual for changes
• This technique is also typically only available to use for well-characterized deletion and duplication syndromes
• Sometimes, it may be difficult to clearly visualize chromosomal alterations such as duplications
• The genes and breakpoints involved in an imbalance may not be clearly defined via FISH

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

• In case Fluorescence in situ Hybridization results are inconclusive, then additional tests such as array CGH may be necessary
• Many laboratories may not have the capability to perform this test. Only highly-specialized labs with advanced facilities and testing procedures may perform this test

Please visit our Laboratory Procedures Center for more physician-approved health information:

http://www.dovemed.com/common-procedures/procedures-laboratory/