Postnatal Diagnosis (Blood Culture)

Reasons for analysis: Chromosome studies are requested where problems that may have a cytogenetic basis are suspected, e.g. babies with birth defects; children with developmental delay and physical handicaps, or adults with fertility problems. Additionally, prospective gamete donors are screened to detect carriers of balanced chromosome rearrangements.

Sample requirements: Lithium heparin whole blood specimens are required – gently mixed to prevent clotting and must not be frozen. Sample volumes may be reduced for children (2-4ml) and neonates (1-2ml).

Turnaround time: The usual turnaround time is approximately two weeks however the laboratory will endeavour to respond to urgent requests. Where a major trisomy is suspected, a rapid PCR screen may be performed to provide an urgent provisional result.

Notes

a)    Rarely, blood samples fail to culture (<1%);
b)    The culture may yield chromosomes of insufficient quality. This will be indicated on the report and a repeat study suggested;

c)    The laboratory should be informed if the patient has recently received a blood transfusion.

Prenatal diagnosis
Reasons for analysis: Chromosome studies are requested where pregnancies are identified as being at risk of a cytogenetic abnormality e.g. advanced maternal age; positive maternal serum screening; fetal abnormalities found on ultrasound; or where a parent is a known carrier of a chromosome anomaly.

Sample requirements:
a)    amniotic fluid – 10ml+ in a plain sterile, leak-proof container. Suitable containers can be provided by the laboratory. The specimen must not be frozen.
b)    chorionic villus – 5mg+ in sterile transport medium. Suitable containers containing medium can be provided by the laboratory. The specimen must not be frozen.
c)     fetal blood – 1-2ml LITHIUM HEPARIN whole blood, gently mixed to prevent clotting.
The specimen must not be frozen.

Turnaround time: This is dependant on the rate of cell growth, however, the usual turnaround time is approximately two weeks. Fetal blood results will usually be reported within 7 days.

Notes
a)    Maternal contamination, and mosaicism may complicate the analysis and may lead to the suggestion that a second invasive test is performed.
b)    Rarely, cultures fail to grow (overall <1%)
c)    Very small chromosome abnormalities may not be detected (this is why the phrase ‘No trisomies or major chromosome abnormalites detected…’ is used in our reports).

Solid Tissue
Reasons for analysis: Fibroblast cultures may be used in addition to blood cultures, for example where tissue specific mosaicism is suspected, or where blood samples cannot be obtained. Analysis may be requested for early spontaneous miscarriages, stillbirths, or to confirm a prenatal diagnosis.

Sample requirements: All specimens should be placed in a sterile container, preferably containing transport medium. This can be supplied by the laboratory. Sterile normal saline can be used if transport medium is not available. Samples must not be placed in formaldehyde or other preservative and must not be frozen.

Turnaround time: This is dependant on the rate of cell growth, however, the usual turnaround time is approximately four weeks.

Notes
a)    Material from miscarriages has a relatively high culture failure rate (around 20%)
b)    If no villus or fetal parts are identified in supposedly POC material and a normal female chromosome result is found, this may indicate that maternal tissue has been cultured (this will be noted on our report)

Fluorescence In Situ Hybridisation (FISH)
Where FISH studies for specific microdeletion syndromes are required this must be indicated on the request form.

Note: FISH studies for a prenatal aneuploidy screen have now been superceded in our laboratory by multiplex-PCR technology and subtelomeric screens are now performed by an MLPA assay.