Microarray testing is ordered when someone 'usually an infant' is found to have developmental delay, intellectual disability, autism, or at least two congenital abnormalities and a diagnosis of the cause cannot be made from the information available from clinical examination, imaging studies and other blood tests. This information can be used to help decide on the level of risk of the same clinical symptoms occurring in subsequent pregnancies.
Because the test can detect very small changes - and we all have some CNVs - it may not be clear if the changes that are seen are the cause of the clinical symptoms. In that case, blood samples from both parents may be taken to see if the finding is also present in one or other parent.
What is being tested?
Microarray testing is a technique that is used for a wide variety of purposes. In diagnostic testing it is primarily used to test for the presence in the patient’s DNA (their genome) of either tiny missing sections (called microdeletions) or extra duplicated sections (called microduplications).
How is it used?
Microarray testing is more sensitive than conventional chromosome studies, called cytogenetics or karyotyping. Although both are able to examine all chromosomes, microarray testing can detect very small changes that cannot be seen using a microscope.
When is it requested?
Microarray testing is ordered when someone – usually an infant – is found to have developmental delay, intellectual disability, autism, or at least two congenital abnormalities and a diagnosis of the cause cannot be made from the information available from clinical examination, imaging studies and other blood tests.
What does the result mean?
The microarray most commonly gives a negative result which means that there are no missing pieces or additional pieces of DNA. If the microarray test does find that there is either missing or additional DNA (called copy number variants) the next step is to assess the significance of the results.
Not all missing or additional pieces of DNA cause problems. Some can be present in a person or multiple members of a family without causing any problems at all. The genetics specialists interpreting the test will look at the case reports to see if the changes found are known to be associated with the problems the patient is having. They will also take into consideration the genes known to be located within the copy number variant segment that has been found. In many cases the same results have been seen previously in other patients and the test result will allow the doctors to make a diagnosis. However, sometimes the significance of the changes found is unknown. This happens quite often because the human genome is enormous (it contains three billion base pairs) so there are many places for variations to occur. If a copy number variant of unknown significance is found, the parents of the child can be tested. If one of them has an identical variant in their DNA but does not have the medical problems found in the child, the variant is less likely to be the cause of the child’s problems.
What does the microarray not test for?
There are several common conditions that will not be detected on the microarray test. These include:
Common questions
In Australia the Medicare schedule will rebate microarray testing in a person, usually a child, with developmental delay, intellectual disability, autism, or at least two congenital abnormalities. Some laboratories may charge more than the Medicare rebate, so there may be an associated out of pocket expense. If the clinical information does not meet these guidelines, the cost may be about $600.
Generally, a result is available within two months.
More information
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