Chromosomal microarray is a high resolution, genome wide screen for the detection of genetic imbalance.
- Higher resolution and abnormality rate than karyotype/chromosome analysis
- Detects microdeletions currently tested for by FISH
To request a microarray test please send blood samples, well mixed, in EDTA (3-5ml) to Cytogenetics. Only one sample tube is required. For patients who are difficult to bleed, we will attempt to process smaller samples.
Please note that blood samples in lithium heparin tubes are not required. Any lithium heparin samples for these referrals will not be processed and they will be discarded.
For parental follow up samples, however, we may still request blood specimens in both EDTA (3-5ml) and lithium heparin (1-2ml) within the probands report. This is because sometimes we need to exclude a balanced parental rearrangement by FISH or karyotype. For sample labelling, sample tube guide and referral form criteria see referral requirements.
For accurate interpretation of the array result include full clinical details of the patient and relevant family members including cytogenetic laboratory references.
Acceptance and rejection criteria
For microarray testing blood in any tube other than EDTA will not be processed. The preferred volume is larger than 1ml but for smaller volumes (>0.25ml) processing will be attempted but the test may be unsuccessful.
Please provide a detailed clinical description because this is required for the interpretation of results. The completion of the Genetic Testing For Neurodevelopmental Disorders form is no longer required for microarray testing, but you may send this if you wish.
Microarray testing has replaced karyotype analysis for patients who fulfil some of the following criteria:
- Developmental delay
- Learning disability
- Facial dysmorphism or congenital abnormalities
- Hypotonic infant
- Congenital heart disease
- Behavioural problems/autistic spectrum
Please refer to the Test Directory published on the NHS England website.
Some copy number changes (CNVs) may be reported as of uncertain significance and cannot be fully interpreted without investigation of parental samples. These will be requested in the report and only a targeted analysis of parental samples will be carried out with respect to the copy number change observed in the original test of the proband. Microarray may detect unexpected genetic CNVs with wider implications for other family members.
Microarray will not exclude:
- Balanced rearrangements
- Point mutations
- Fragile X
- Single gene disorders
- Some cases of Prader-Willi or Angelman Syndrome
- Some cases of mosaicism
Please indicate at referral if additional testing for the conditions listed above is required.
Please see our Target Reporting Times.
Please see our postnatal limitations of testing.
Storage and further testing
DNA from EDTA samples is stored within Molecular Genetics for possible future tests.
Page last updated 30/09/2021. Please note that if printed, the information is only valid on the day of printing.