The Principles of Clinical Cytogenetics - Extra Materials - Springer

Quality Control and Quality Assurance 105
Specimen Failures
The inability of a laboratory to provide a diagnostic result is typically the result of one of two basic
reasons: cells from the sample do not grow in culture and, therefore, no mitotic cells are produced, or
a problem occurs in one of the many postculture steps, rendering the processed material useless. The
purpose of this subsection is not to convince the reader that problems are inevitable, but rather to
impress upon him or her the amount of care and attention to detail required and the critical role
quality assurance plays in the cytogenetics laboratory.
Culture Failure
As described in Chapter 4, the basic procedure for producing chromosomes for analysis from any
tissue type requires living cells that can somehow be coaxed into active division. Without mitosis,
there can be no chromosomes to process and examine.
There are several possible reasons for cell culture failure:
• The sample did not contain any living cells. In some cases, this is clinically not surprising; it is
frequently the case with products of conception obtained from fetal demise or in necrotic or aplastic
bone marrow samples. Other times, one can deduce the cause (such as a delay in sample transport
or exposure of the specimen to extremes of temperature during transport when an outside
reference lab is used). In still other instances, no explanation is readily available. In these cases,
the entire path the specimen followed between the point of collection and delivery to the laboratory
is suspect and must be investigated.
• An inappropriate specimen is submitted to the laboratory. This could involve peripheral blood
with no circulating blasts being collected instead of bone marrow. (Without blasts in the periphery,
there are no spontaneously dividing cells present and the unstimulated cultures used for hematopoietic
disorders will not produce metaphases.) It might be the result of the wrong collection
tube being used, or of products of conception being placed in formalin and then sent to the lab. The
specimen and the way it is collected must match the intended application of chromosome analysis.
• An insufficient specimen is submitted to the laboratory. For example, “2 mL of extremely bloody
amniotic fluid” or “0.5 mL of watery bone marrow” is the type of description that frequently
accompanies a culture failure record. It should be pointed out, however, that all such samples
should be submitted to the laboratory, which will do everything it can to generate a result, no
matter how unlikely this may seem.
• The laboratory suffers a catastrophic equipment failure. With proper precautions in place, this is
unlikely. Specimens should be divided and multiple cultures, placed in separate incubators, should
be initiated whenever possible. There should also be appropriate backup power, redundant CO 2
and alarm/warning systems in place, and all major equipment should be on a preventative maintenance
schedule. Nevertheless, unusual hardware problems do occur.
• Reagent failure. There are rare but unfortunate examples of supplies that are supposedly quality
controlled by the manufacturer being released (unknowingly) for purchase by laboratories without
actually meeting the appropriate criteria. Improperly cleaned water storage tanks have poisoned
entire lots of culture medium, and syringes made with natural rubber stoppers have periodically
resulted in amniotic cell death on contact. Again, with proper precautions in place (testing all
supplies before use and dividing all cultures between two lots of everything), this risk can be
minimized.
• Human error. Although also unlikely, it is always possible for a technologist to inadvertently
prepare culture medium incorrectly, forget to add the appropriate mitogen, or utilize equipment
improperly.