Biology of Disease

HOSPITAL LABORATORY TESTS

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Report

delivered to

doctor

Initial

examination

of patient by

doctor

Action

Initiates

request

Sample(s)

from patient

Transport

Laboratory

reception

Specimen

identification

Laboratory

worklist

Specimen

preparation

Specimen

aliquots

Result(s)

Calculation(s)

Analysis(es)

Quality

control

Report

Report

evaluation

Reexamination of

patient &

interpretation of

report by doctor

Figure 1.18 Sequence of events involved in

obtaining a clinical test result.

For some analytes, the blood must be collected into a tube containing an
anticoagulant or preservative. Specimens of blood for glucose determination
must be collected into a tube containing fluoride ions (F–) since this inhibits
glycolysis and prevents the utilization of serum glucose by blood cells.
Occasionally blood is collected into the wrong tube and then decanted into
the correct tube. This can cause a number of problems. For example, blood
collected into a tube containing ethylene diamine tetraacetate (EDTA) will be
unsuitable for the determination of serum Ca2+, since EDTA is an anticoagulant,
works by chelating and removing available Ca2+.

The transport of specimens and their storage must be considered carefully
since an inappropriate environment can influence the values of clinical test
results. Swabs, for example, obtained during a microbiological investigation
of an affected site, contain only a small volume of specimen and dry easily.
They therefore need to be transported to the laboratory as quickly as possible

Figure 1.19 Photograph of some tubes used in

the collection of clinical specimens. Courtesy of

BUPA Hospital, Manchester, UK.