Blood Chromosome Analysis This is performed on a 5-10ml fresh, sterile sample of venous blood in a lithium heparin container. The sample should be well mixed. “Heel stab” samples, which are non-sterile, are unsuitable. In infants the analysis can be done on a minimum of 2ml, however, the chances of successful culture diminishes with the size of the sample.
Lymphocyte cultures are set up and allow visualisation of chromosomes in lymphocytes which are undergoing cell division (mitosis).
The results of routine lymphocyte chromosome studies are available from between 21 and 28 days after receipt of the specimen.
The results of urgent specimens are available from between 7 and 10 days after receipt of the specimen. Specimens treated as urgent include all samples from infants less than one month, pregnant women and their partners, and specimens where an urgent result has been requested by the referring clinician. Common reasons for carrying out blood chromosomal analysis are:
In these situations a constitutional chromosome abnormality is sought - ie. one which has been present since conception and affects cells distributed throughout an affected individual. Such abnormalities may comprise an alteration in the structure of a chromosome or an entire extra (or missing) chromosome. If the net result of a constitutional abnormality is duplication or deficiency of chromosome material (termed ‘unbalanced’), then adverse clinical effects (mental / physical handicap) are likely.
If the constitutional structural abnormality has simply resulted in re-arranged chromosome material, (i.e. no duplication or deficiency, termed a ‘balanced’ rearrangement), no adverse effects are likely although the individual carrying such a rearrangement may be predisposed to having a handicapped child with a derivative ‘unbalanced’ chromosome constitution.