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Although not all infectious diseases require a diagnostic laboratory
intervention (eg, uncomplicated otitis media), clinicians often
rely on laboratory tests to help identify a causative agent, select
an appropriate antimicrobial agent, and/or assess response
to therapy. It is imperative that clinicians have a basic understanding
of diagnostic microbiology so they can obtain appropriate samples
and order the most appropriate test for diagnosing the condition
they are suspecting and selecting the most appropriate therapy (Table 226-1). Often, consultation with the
microbiology laboratory is useful to determine which test would
be most appropriate for the suspected disease.
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It is important to recognize that molecular biology has influenced
the way in which infectious diseases are diagnosed.49 DNA
and RNA amplification by PCR has become an important resource in
the diagnosis of infections. PCR has been shown to be more sensitive
than in situ hybridization. It can detect as few
as 10 to 100 copies of nucleic acid, whereas hybridization detects
only 10,000 copies. PCR has been useful for identifying slow-growing
organisms such as Mycobacterium tuberculosis and Borrelia burgdorferi;
Rickettsia, and, potential agents of bioterrorism.153 Molecular
fingerprinting has become a useful resource in the investigation
of nosocomial infections and has fostered the field of molecular
epidemiology.154-156
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Collection and Processing
of Clinical Specimens
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No degree of laboratory expertise can correct the error of inappropriately
collected and transported specimens. The proper collection and handling
of clinical specimens is as important as selecting the correct medication
for treatment.1,2 Common problems with ...