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Paediatric tests

Sample requirements

Samples should ideally be sent to the Cytogenetics Department on the same day/next day. Where a delay is inevitable, such as over weekends, please store the sample in a refrigerator before sending on the next working day but please DO NOT FREEZE. Lithium heparin and EDTA tubes are suitable for cytogenetic testing depending on the test required, please see below, samples in other tubes will be rejected. For sample labelling, sample tube guide and completion of referral form criteria please see referral requirements.

Karyotype and FISH

Please send a 1-2ml blood sample, well mixed, in a lithium heparin (usually green cap) container. Gel tubes may be used but please do not centrifuge or allow to separate. For neonates or children who are difficult to bleed we will attempt to process smaller blood samples.

Chromosomal Microarray

For microarray please send a 3-5ml blood sample in an EDTA container. Only one EDTA tube is required. Bloods in other tubes will not be processed.

Fanconi Anaemia

Fanconi Anaemia referrals should be sent to Sheffield Diagnostic services. Please see SDGS website for details.

Acceptance and rejection criteria

Lithium heparin is the preferred tube for karyotype testing. Bloods received in EDTA will be processed but the quality may be compromised. Bloods in any other tube will not be processed. For paediatrics the volume required is 1-2ml, smaller volumes may be attempted but the success or quality of the test may compromised.

For urgent referrals or unrepeatable samples, if blood samples are received clotted or haemolysed, processing is usually attempted, however this may compromise the success or quality of the test. For a routine referral, the sample may be rejected and a repeat sample requested.

Referral categories and tests

Chromosomal microarray 

Microarray will be performed as appropriate depending on the clinical indication. For further information about the testing available and the clinical eligibility for these tests please refer to the National genomic test directory for rare and inherited disease and the Rare and inherited disease eligibility criteria. Please select the most appropriate code for the tests required.

For optimum interpretation of a microarray result, please provide a full clinical description of the patient.

If tests in addition to a microarray are required, please use appropriate code(s) for this from the test directory.

Some copy number changes (CNVs) may be reported as of uncertain significance and cannot be fully interpreted without investigation of parental samples. If required, parental blood samples will be requested in the report and a targeted analysis carried out for the copy number change observed in the original test of the proband. Microarray may detect incidental CNVs which may have implications for other family members.

Microarray will not exclude:

  • Balanced rearrangements
  • Small nucleotide variants (SNVs)
  • Fragile X
  • Single gene disorders
  • Some cases of Prader-Willi or Angelman Syndrome
  • Some cases of mosaicism

Karyotype

Karyotype analysis will be carried out as appropriate depending on the clinical indication. For further information about the testing available and the clinical eligibility for these tests please refer to the National genomic test directory for rare and inherited disease and the Rare and inherited disease eligibility criteria. Please select the most appropriate code for the tests required.

Targeted G- banding will be carried out for a known chromosomal rearrangement e.g. a known familial rearrangement, aneuploidy detected by FISH/QF-PCR/microarray testing; a particular pattern of segmental variants detected by microarray analysis suggestive of a balanced parental rearrangement. 

FISH - Fluorescence In Situ Hybridisation

FISH may be carried out to test for trisomy 13, 18 or 21 and numerical sex chromosome abnormalities. Microarray analysis is more appropriate test for microdeletion syndromes.

Other FISH testing may be suitable for certain familial cytogenetic rearrangements. Please contact the laboratory to discuss this testing prior to ordering a test.

Limitations

Please see our limitations of testing page.

 

Storage and future testing

Fixed cells from neonate and paediatric samples are archived for at least six months from the date of receipt of the sample. Cases with a normal karyotype are then discarded; cases with a structural chromosome abnormality are stored for five years. For samples referred for microarray testing, the remaining DNA is stored for at least 30 years within Molecular Genetics. Subsequent genetic testing can be requested at any time within these periods but may not be possible depending on the quality of the stored DNA.

Page last updated 24/09/2026. Please note that if printed, the information is only valid on the day of printing.