CLINICAL USE OF LABORATORY STUDIES
Physicians select laboratory studies and interpret
the results. They integrate their laboratory interpre-
tations into the clinical assessment through the
synergistic interplay of quantitative analysis and
clinical judgment. This process, which occurs
repetitively throughout the care of a patient (Figure
1.1) constitutes the general pattern of use of labora-
tory studies.
If a laboratory study is to provide clinically
useful information, it must be ordered with a
specific clinical goal in mind (Table 1.1). The clini-
cian relates each goal to a set of specific information
needs based upon a pathophysiologic understanding
of the disorder or disorders under consideration
(Table 1.2).
For example, one medical goal in a patient with
severe chest pain is to establish or exclude the
diagnosis of acute myocardial infarction. Infarction
means cell death so the foremost information need is
to determine if myocyte death has occurred. In
addition, though, the information needs might
include an assessment of cardiac function and
electrophysiology as infarcts typically cause regional
contractile dysfunction and impaired myoelectric
signal propagation in the ischemic myocardium.
Having identified the information needs for a
patient, the clinician then orders clinical and labora-
tory studies to address the needs, here also depend-
ing upon pathophysiologic principles to select and
interpret the studies. For instance, in pursuing the
question of cardiac myocyte death in the patient with
chest pain, the clinician will request that the plasma
concentration of creatine kinase-MB be measured
because there is a reliable pathophysiologic relation-
ship between the plasma concentration of this
enzyme and the presence of myocyte death.
The interpretations of the study results and of
additional clinical observations provide the input for
reevaluation of the clinical assessment and revision
of the catalog of medical goals for the patient. And
the cycle begins again.
This simple picture of study use does not,
however, take into account a number of real-life
considerations including (1) limitations in the avail-
ability of studies, (2) delays in the time it takes to
receive study results, and (3) the physical, psycho-
logical, and financial costs of performing studies.
When planning the laboratory evaluation of a
patient, the clinician must keep in mind the capabili-
ties of the clinical laboratories. Not every study is
available at every hospital. Fortunately, the
standards of medical care in developed countries are
so high that, usually, when a laboratory study is not
available, either an adequate substitute study is, or a
specimen can be sent to a reference laboratory, or
the patient can even be transferred to a medical
center that does offer the study. The availability of
laboratory studies can also be constrained by limita-
tions in the schedule for study performance—a study
that cannot be done when needed may be no better
Laboratory-based Medical Practice
1-1
Interpretation
of results
Laboratory
study results
Clinical
assessment
Interpretation
of observations
Clinical
observations
Selection of
laboratory studies
Selection of
clinical studies
Determination of
additional clinical
information needs
Figure 1.1
Cyclic structure of the use of medical studies.
Chapter 1
LABORATORY-BASED MEDICAL PRACTICE
© 2001 Dennis A. Noe
