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Cytogenetic Testing: Fluorescent In Situ Hybridization (FISH) Testing

Also known as: FISH testing, congenital blood test, cytogenetic testing.

What is cytogenetic testing: fluorescent in situ hybridization testing?

The FISH (fluorescent in situ hybridization) test is a blood test that “maps” the genetic material in a child’s cells looking for gene abnormalities which can give rise to developmental delays, autism, mental retardation and other rare genetic disorders that sometimes occur at birth.

What happens during the procedure?

A small amount of blood is drawn in the usual way from a child’s vein and sent to the genetics laboratory for testing.

Is any special preparation needed?

No special preparation is needed for this test.

What are the risk factors?

There are slight risks of infection, bleeding, bruising, swelling or damage to nearby structures when the blood is drawn.

Reviewed by: Jack Wolfsdorf, MD, FAAP

This page was last updated on: 9/16/2025 12:48:11 PM

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Autism Autism refers to a group of neurodevelopmental disorders that makes it difficult for a child to interact socially, communicate verbally and non-verbally and connect with people.
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