Chapter VIL TUBERCULIN AND ITS VALUE IN DIAGNOSIS
Tuberculin, carefully used in proper doses and properly interpreted, is free from danger, and may be of great value in the diagnosis of early tuberculosis; in the hands of those not skilled and experienced in its use, however, it can do much harm. The general practitioner will never find it an agent of much value except in the diagnosis of tuberculosis in young children; even here a positive reaction by no means necessarily signifies that tuberculosis is the cause of the symptoms. In practically no ease should a diagnosis be based on the result of a tuberculin test alone without other confirmatory evidence, nor should it be used until all other means of making a diagnosis have failed.
In the great majority of cases a positive reaction means that tuberculosis is present somewhere in the body; but in the absence of any focal reaction, i.e., local hyperemia or other signs of renewed activity in the lungs, glands, joints or wherever the suspected focus may be, a positive reaction does not give any information as to whether the tuberculosis is active or latent, old or recent, or where it is located.
A negative reaction likewise by no means proves that there is no tuberculosis, except in the case of young children under five years, and indeed not always then. In the case of adults, a negative reaction may mean no tuberculosis. This is very unlikely, however. It is more apt to mean that the patient has already established an immunity to the disease and therefore no longer reacts to that particular dose of tuberculin. The test is occasionally negative during or following certain acute diseases, such as measles; finally, a negative reaction frequently occurs in patients who are either so advanced in consumption, or who for some other reason have insufficient vitality to produce anti-bodies to thus cause a reaction. It is of the greatest importance to bear in mind these causes of a negative reaction. Many patients have been lulled into a false sense of security because of a negative tuberculin test.
Among the various methods of using tuberculin for diagnostic purposes, the subcutaneous test is by all means the most reliable; it is also the most difficult to carry out properly and to interpret correctly. The patient should be in bed in order to get satisfactory results. The test should not be given where there is over one-half degree of fever, where there has been recent hemorrhage or where renal tuberculosis is suspected. The initial dose should not be over .1 mg. of Koch’s old tuberculin; the second dose, in case there is no reaction to the first in forty-eight hours, should contain 1 mg., and the third, which is not usually necessary, 10 mg. Patients should be kept in bed during the forty-eight hours following each injection. This should be given in the late afternoon so that the patient need not be disturbed during the night for purposes of temperature taking. Temperature and pulse should be recorded for two days every two hours when possible. Signs of a focal reaction,—local hyperemia or other signs of activity in the suspected part, such as increased cough and sputum, increased pain, redness or swelling in glands, joints or elsewhere,—or a local reaction, swelling, redness and pain at the point of injection are more important and less subject to error than constitutional disturbances.
The cutaneous tuberculin reaction is perfectly safe and is easy to apply; a positive or negative result in adults is, however, of far less significance than the subcutaneous test. The form of test most frequently used is that first described by Von Pirquet, whose name is frequently attached to this method. It consists in scarifying the skin of the upper arm with a needle, lancet, or other instrument under aseptic precautions and rubbing in with the instrument a drop of Koch’s old tuberculin; another vaccination should be made at the same time above the first, using sterile water instead of tuberculin in order to be able to compare the two scarifications and to rule out any abnormal inflammatory reaction. The scarification should be deep enough to bring out serum but not blood. Excess of fluid should be drawn off and the rest allowed to evaporate. No dressing is needed.
There are various degrees of a positive reaction, from a small indurated red spot not over 4 inch in diameter to a large inflamed area 1 to 1} inches in diameter, red and occasionally covered with yellow blisters. A modification of this test is the intra-cutaneous test, whereby a small amount of diluted tuberculin is injected with a syringe not underneath the skin but into the skin itself. The third method consists of rubbing into the skin some ointment to which a certain amount of tuberculin has been added. This is the Moro ointment test. Neither this nor the intra-cuticular method has any advantage over the simpler Von Pirquet skin test.
A few years ago Calmette described the ophthalmic tuberculin reaction. This consists of introducing into one conjunctival sac a few drops of dilute ophthalmic tuberculin. A positive result is striking but often annoying to the patient, and occasionally the cause of permanent injury to the eye. Practitioners are advised not to use this method.
The sub-cutaneous tuberculin test, applied under proper conditions and interpreted by one skilled and experienced in its use will give valuable and trustworthy evidence as to the presence or absence of tuberculosis somewhere in the body; in case of a local reaction in the lungs as shown by increased rales, cough and sputum, it may give evidence as to the presence of active pulmonary tuberculosis. On the other hand, if performed by those not skilled in its use, it is capable of doing great harm not only by lighting up old quiescent processes, but by a wrong interpretation.
The Von Pirquet cutaneous test is of undoubted value in children, especially those under five years. The older the patient the less the significance of this test, so that in adults very little value in diagnosis can be attached to it. As a general thing it is safer to leave these tests to those who have made them a special object of study. No form of tuberculin test will ever equal or approach in value the evidence gained by a careful history of the patient and a detailed, painstaking physical examination.
<Callout type="warning" title="Safety Hazard">Do not use the ophthalmic tuberculin reaction method as it can cause permanent eye injury.</Callout>
<Callout type="tip" title="Pro Technique">For subcutaneous tests, ensure the patient is in bed and has no fever or recent hemorrhage to avoid false negatives or positives.</Callout>
<Callout type="important" title="Critical Rule">Never base a diagnosis solely on tuberculin test results; always use other confirmatory evidence.</Callout>
Key Takeaways
- Tuberculin tests can be valuable but must be interpreted carefully.
- Subcutaneous tests are more reliable than cutaneous ones.
- Do not use the ophthalmic tuberculin reaction method due to risks of eye injury.
Practical Tips
- Always perform a thorough physical examination before and after using tuberculin tests.
- Ensure the patient is in bed during subcutaneous tests to avoid false results.
- Use multiple forms of evidence, not just tuberculin tests, for accurate diagnosis.
Warnings & Risks
- Do not use the ophthalmic tuberculin reaction method as it can cause permanent eye injury.
- Avoid performing tuberculin tests on patients with fever or recent hemorrhage to prevent false results.
- Interpretation of tuberculin test results requires skill and experience; improper interpretation can lead to misdiagnosis.
Modern Application
While the specific techniques for diagnosing tuberculosis using tuberculin are outdated, understanding the importance of accurate diagnosis and the risks associated with incorrect methods remains crucial. Modern diagnostics have improved significantly but still rely on careful examination and multiple forms of evidence, much like this historical chapter emphasizes.
Frequently Asked Questions
Q: What is the significance of a positive reaction in tuberculin tests?
A positive reaction generally indicates that tuberculosis is present somewhere in the body. However, it does not provide information about whether the tuberculosis is active or latent, old or recent, or where exactly it is located.
Q: Why should a diagnosis not be based solely on tuberculin test results?
Tuberculin tests can give false positives or negatives. Therefore, they should always be used in conjunction with other diagnostic methods and confirmatory evidence to avoid misdiagnosis.
Q: What are the risks associated with using the ophthalmic tuberculin reaction method?
The ophthalmic tuberculin reaction can cause permanent eye injury. It is recommended not to use this method due to its high risk of harm.