Biology of Disease

1.12 Summary

Health is a ‘state of physical, mental and social well-being, not merely the
absence of disease’. Disease refers to any abnormality or failure of the body
to function properly. For medical treatment to commence the disease needs
to be diagnosed and its etiology established. This also helps to define the
prognosis, that is, the likely course of the disease and its outcome. Diseases
have a number of possible causes. They may be exogenous, such as infections
or trauma (accidents) or they may be endogenous such as diabetes or cancer.
Some diseases may be caused by a range of factors and are called multifactorial
and, for some, the cause may be unknown and these are referred to as
idiopathic.

The pathogenesis describes how the etiological agent produces the clinical
signs and symptoms and the pathological changes characteristic of that disease.
This enables the physician to make a diagnosis and prescribe treatment. The
prognosis should also emerge at this stage.

Diseases may be classified into a number of types: genetic, infectious,
endocrine, traumatic, degenerative, immunological, nutritional, homeostatic,
neoplastic (cancer), toxic, psychogenic and iatrogenic (caused by the treatment
itself ). Epidemiology is the study of how diseases spread in populations. This
is of importance in the control of diseases.

Various types of laboratories specialize in investigating the pathology of
diseases. A laboratory may measure the concentrations of analytes in blood
and urine, identify infectious agents such as bacteria and viruses, characterize
genetic diseases by looking at the patient’s chromosomes, or identify problems
with the blood, for example those involving defective hemoglobin or clotting
factors. The laboratories report their findings to the clinician in charge of
the patient to help in the process of diagnosis and in making decisions on
treatment and how well any treatment is working. Pathology laboratories
must work to high standards of accuracy, otherwise wrong treatments may be
given and patients may be misinformed about their disease and its prognosis.
Therefore pathology laboratories take steps to standardize and check their
procedures on a daily basis and investigate new tests exhaustively before they
are introduced.

SUMMARY

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CASE STUDY 1.2

A new test for the detection of prostate cancer has

been developed and is undergoing clinical evaluation

to determine how effective it is in the diagnosis of this

condition. The study included 100 healthy men and 100

men with known prostate cancer. All were screened using

the new test, which involved the measurement of a serum

tumor marker. The patients were rated either positive

or negative depending on whether the determined

concentration of the tumor marker was above or below

a certain cut-off value. The results obtained were as

follows:

Positive Negative

Patients with prostate cancer 95 5

Healthy individuals 595

Question

What are the sensitivity and specificity of the test? Discuss

the values.