Section Menu

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: September 16, 2025 12:48 PM

Genetic and Metabolic Disorders

Certain pediatric health conditions have a root cause in genetics

Learn More
Check Your Symptoms
Use the symptom checker tool to check how serious your symptoms are, if a healthcare visit is needed, and what steps you can take to relieve your symptoms at home.

Learn more about

Genetic Diseases

Genetic diseases are conditions that occur due to a mutation in a gene in the body’s cells.

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.

Developmental Delays

Whenever a child fails to reach a set of developmental milestone for physical/motor, in language and communication, social, or behavioral function, and/or cognitive ability at their expected time, it's known as developmental delay.

Blood Labs

Blood labs is a short-hand or slang phrase for blood laboratory tests. These are common medical tests used in the diagnosis of a wide variety of medical conditions.