The Indian Journal of Tuberculosis - LRS Institute of Tuberculosis ...

Continuing Medical Education Ind. L Tub., 1992, 39, 53
TUBERCULIN SKIN TEST*
A.N. Sashidhara 1 and K. Chaudhuri 2
Introduction
The tuberculin skin test has a 100 year old
chequered history. Its use and validity were very
different at the start compared with what they are
today.
After the discovery of the tubercle bacillus in
1882, Robert Koch began experimenting with its
growth on culture media in the laboratory. By
1890, he had developed a brownish, transparent,
broth culture filtrate which he named “tuberculin”.
Soon followed his announcement that tuberculin
“protected against tuberculosis in guinea
pigs, and had a specific healing effect on tuberculosis
processes of all kinds in human beings”,
which claim proved to be baseless. However, his
observation that the “subcutaneous inoculation of
tuberculin in a tuberculous patient led to a rise in
temperature and local reaction at the inoculation
site, whereas it had no such effect on the non-tuberculous”
laid the foundation at that time, for its
use in the diagnosis of tuberculosis. However,
neither a standard tuberculin preparation nor a
uniform technique for testing was developed.
In 1907, Von Pirquet demonstrated that on
skin “a tiny scratch made through a little quantity
of tuberculin.... produced evidence of tuberculin
sensitivity”, which observation was the next step
in the long journey towards the present day tuberculin
test. In 1908, Charles Mantoux used a syringe
to administer a measured quantity of tuberculin,
at a desired depth in the skin (Mantoux
test), which has since become the standard procedure
for doing the tuberculin skin test. No doubt,
several other methods for doing the test have
been developed but none can be standardized,
qualitatively and quantitatively, as is possible with
the Mantoux test.
In order that the test could be used, by clinicians
to identify persons at a higher risk of developing
tuberculosis and epidemiologists to meas-
ure the extent of tuberculosis infection in the
community, Carrol E. Palmer and his co-workers
identified, around 1950, most of the shortcomings
of the tuberculin skin test, and developed ways to
overcome them. Their monumental researches
led to the desired standardization of the test, thus
retaining its value as a reference test for other
competing tuberculin tests. They showed that a
significant reaction (say > 10 mm) merely indicated
infection with M. tuberculosis, and the person
being at a higher risk of developing the disease.
The isolation of tubercle bacillus, from a
specimen obtained from a person and/or detection
of characteristic tissue changes in a biopsy
specimen was essential to establish the definitive
diagnosis. In other words, even the currently used
standard tuberculin skin test has shortcomings,
which are being overcome by a very careful interpretation
of the results, making it a very valuable
epidemiological tool, but hardly a-diagnostic test.
Tuberculins
Currently, two main tuberculin preparations
are in use:
Old Tuberculin (OT) which is a M tuberculosis
broth culture, containing soluble portions
of the used culture medium and lysis
products of one or more strains of the bacillus,
filtered and concentrated to a desired
volume; and
Purified Protein Derivative (PPD) which is
a pure mixture of protein polysaccharides
derived from the bacillus by a process
developed by Seibert et al.
The OT is a crude product containing many
extraneous agents that produce cross reactions to
many mycobacteria of non-tuberculosis type. The
composition and quantities of the active principles
in different preparations of OT are never
* Abridged and condensed from : The Tuberculin Skin Test - Emerging 100 years since its first use\ NTI Newsletter
(1990), 26, 1 & 2, Supplement.
1. Investigator; 2. Director, National Tuberculosis Institute, 8, Bellary Road, Bangalore- 560 003.