The Principles of Clinical Cytogenetics - Extra Materials - Springer

64 Martha Keagle and Steven Gersen
can be processed. Culture medium is sometimes added to small blood samples, as these have a tendency
to dry up, especially if collected in large containers.
A repeat sample should be requested if these requirements are not met (e.g., the sample is received
clotted, on ice, more than 24 hours old, etc.). It is not always practicable or possible to obtain a new
sample, and in such cases, the laboratory should attempt to salvage the original specimen. There may be
enough viable cells for a cytogenetic analysis, although the number and quality of cells may be compromised.
Requirements: Bone Marrow Aspirates
The collection requirements for bone marrow samples are essentially the same as for peripheral
blood. Bone marrow aspirates should be collected in sterile syringes or vacuum tubes containing
preservative-free sodium heparin and transported at room temperature. The first few milliliters of the
bone marrow tap contain the highest proportion of cells and are the best sample for the cytogenetics
laboratory. Blood dilutes the bone marrow sample in later taps and reduces the number of actively
dividing cells present in the sample. The success of bone marrow culture is dependent on the number
of actively dividing cells. Bone marrow specimens should be processed without delay upon receipt to
avoid cell death.
Requirements: Amniotic Fluid Specimens
Amniocentesis can be performed from as early as 10 weeks gestation until term (see Chapter 12).
From 15 to 30 mL of amniotic fluid should be obtained under sterile conditions and collected in a
sterile container approved for cell culture. For amniocentesis performed earlier than 15 weeks, 1 mL
of fluid is generally drawn for each week of gestation. The first few milliliters of an amniotic tap are
the most likely to be contaminated with maternal cells and should not be submitted to the cytogenetics
laboratory. Samples should be transported at room temperature. Temperature extremes and long
transport times should be avoided.
The amniocentesis procedure has an inherent, albeit small, risk of miscarriage and should not be
repeated unless absolutely necessary. Every effort to salvage samples improperly collected or handled
should be made to diminish the need for a repeat tap.
Requirements: Solid Tissue Specimens
Solid tissue sources include skin biopsies, chorionic villi, products of conception, and stillbirth
biopsies. Products of conception and stillbirths are one-of-a-kind specimens that cannot be recollected,
and repeat collection of chorionic villi increases the risk of abortion, although subsequent
amniocentesis is an option here. Microbial contamination is a common problem for many types of
solid tissue samples. Unlike amniotic fluid, blood, bone marrow, and chorionic villi, most solid tissue
specimens are not sterile prior to collection. In addition, viable cells might be few or even nonexistent.
These factors threaten the integrity of the sample and pose problems for the laboratory.
Small samples should be collected and transported in sterile culture vessels containing growth or
tissue culture medium (not formalin). Sterile saline is not optimal for this purpose, but should be used
if no other option is available. If distance and timing permit the laboratory to receive and process the
sample at once, it can be delivered with no liquid added at all. Larger samples can be sent to the
laboratory in toto for dissection. Solid tissue samples should be transported and stored on ice until
culture is established. Storing tissue specimens on ice slows the action of enzymes that degrade the
tissue and slows microbial growth in the event of contamination.
CULTURE INITIATION
Growth Media
All specimens for chromosome preparation are grown and maintained in an aqueous growth
medium. Some media are formulated for specific cell types (e.g., AmnioMax ® or Chang ® for