CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
Clinical versus Statistical Significance
There are two major types of variations: analytical and biological. Analytical
variation would occur due to functions of the machines, reagents, and other
conditions difficult to determine. Biological variations occur due to differences
between groups of peoples based on genetics and on lifestyle factors such as
diet and cultural practices. For example, a physician would have to weigh any
biological differences with the test results before forming informed conclusions
regarding the health of an individual. Clinical significance has little to do with
statistics and is subject to a medical professional’s interpretation and judgment.
Therefore, results can be statistically significant yet clinically insignificant.
To determine if figures are clinically significant, the SDs for repeated measurements
on a single QC specimen are compared with the SDs for repeated
measurements made at weekly intervals within a group of healthy subjects over
a period of 10 weeks, which allows for seasonal variations. While clinical significance
derives from a calculation for statistical significance, it is usually a matter
of clinical judgment. In clinical trials for certain medications or procedures,
results are treated as significant when the chance that the difference between two
groups occurred is less than 1 time in 20.
Clinically Consistent
If the value derived does not match the clinical diagnosis, research to find an
explanation must be pursued. Was the sample identified correctly? What was
the method of collection? Did a repeat sample give similar results? If not, the
diagnosis may be in error. This is the reason that laboratory workers must have
an adequate knowledge of anatomy and physiology, and of disease states that
may affect other values. It requires experience and observation before the critical
thought processes reach the point that the technologist or technician is able correlate
sets of values, often from different departments of the laboratory.
Specificity and Sensitivity
Specificity is the measure of the incidence of true negatives in persons known
to be free of a disease. If a certain procedure is specific in measuring for a disease,
persons with clinical manifestations of the disease should test qualitatively
positive, and in quantitative tests, results should be considerably elevated or
decreased.
Sensitivity is incorporated into test procedures where changes in certain
metabolic processes in the body can be measured at levels that are clinically
significant. Sensitivity should not be so great that an analyte normally found in
low levels in the body will give a false positive result. But a procedure must be
sensitive enough to detect levels that indicate the presence of a certain disease
when low levels are clinically significant. When the sensitivity of a procedure is
optimal, only levels that are in a certain range indicating a specific disease will
yield a result that will be helpful in diagnosing the presence of a disease or medical
condition requiring medical attention.
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