Tuberculin: Medical Uses, History, Dosage, Reading Method, Interpretation, Secondary Effects and Controversy

Also known as purified protein derivative, it is a combination of proteins that are used in the diagnosis of tuberculosis.

This use is known as the tuberculin skin test and is recommended only for people at high risk. The injection is done on the skin.

After 48 to 72 hours if there is more than one swelling area of ​​five to ten millimeters, the test is considered positive.

Common side effects include redness, itching and pain at the injection site. Allergic reactions can occur occasionally.

The test may be falsely positive in those who have been previously vaccinated with the Bacillus Calmette-Guérin vaccine (BCG) or have been infected with other types of mycobacteria.

The test can be falsely negative within 10 weeks of infection, in children under 6 months and in those who have been infected for many years. The use is safe in pregnancy. The tuberculin is made from an extract of Mycobacterium tuberculosis.

Tuberculin was discovered in 1890 by Robert Koch . It is on the list of essential medicines of the World Health Organization, the most effective and safe medicines that are needed in a health system.

The wholesale cost in the developing world is approximately 0.22 USD per dose. In the United States, tests cost less than USD25.

Medical uses of tuberculin

The tuberculosis skin test is used to determine if someone has developed an immune response to the bacteria that causes tuberculosis (TB). This response can occur if someone currently has tuberculosis, if he was exposed to it in the past.

The test used in the United States today is known as the Mantoux test. An alternative test called the Heaf test was used in the United Kingdom until 2005, although the United Kingdom now uses the Mantoux test in line with the rest of the world.

Both tests use the tuberculin derivative PPD (purified protein derivative).

The World Health Organization estimates that 2 billion people in the world have latent tuberculosis, while around 3 million people in the world die from tuberculosis each year. The tuberculosis skin test is also known as tuberculin skin test or PPD test (purified protein derivative).

The tuberculin skin test is based on the fact that infection with M. tuberculosis bacteria produces a delayed-type hypersensitivity skin reaction to certain components of the bacterium.

The components of the organism are extracted from tuberculosis cultures and are the central elements of the classical purified tuberculin protein derivative test (also known as purified protein derivative).

This material derived from purified protein is used for tuberculosis skin tests.

The skin reaction to the purified protein derivative of tuberculin begins when specialized immune cells, called T cells, which have been sensitized by a previous infection, are attracted by the immune system to the site of the skin where they release chemical messengers called lymphokines.

These lymphokines induce induration (a hard, raised area with clearly defined margins in and around the site of injection) through local vasodilation (expansion of the diameter of the blood vessels) that leads to fluid deposition known as edema, deposition of fibrin and attraction of other types of inflammatory cells in the area.

In general, an incubation period of two to 12 weeks after exposure to the TB bacterium is necessary for the purified protein derivative test to be positive.

Anyone can undergo a tuberculosis test and it can be given safely to infants, pregnant women or HIV-infected people. It is only contraindicated in people who have had a severe reaction to a previous tuberculin skin test.

The recommended standard tuberculin test is administered by injecting 0.1 ml of a liquid containing 5 tuberculin units (PPU) into the purified protein derivative test in the upper layers of the skin (intradermally, immediately below the surface of the skin). skin) of the forearm.

The use of an area of ​​skin that is free of abnormalities and away from the veins is recommended. The injection is usually done with a 27-gauge needle and a tuberculin syringe.

The PPD tuberculin is injected just below the surface of the skin. A discreet and pale elevation of the skin (a welt) of 6 mm to 10 mm in diameter should be produced when the injection is done correctly.

This wheal or “blister” is usually absorbed quickly. If it is recognized that the first test was administered incorrectly, another test can be performed at a time, selecting a site several centimeters away from the original injection.

History

Tuberculin was discovered by the German scientist and physician Robert Koch in 1890. The original tuberculin discovered by Koch was a glycerin extract of the tubercle bacillus and developed as a remedy for tuberculosis, but the reductions in deaths did not meet expectations. of the treatment.

The British efforts to establish “dispensaries” for the examination, diagnosis and treatment of the poor achieved better results, since the structure of the Edinburgh System covered the treatment of households and full contacts of tuberculosis patients.

The example of Dr. Hilda Clark’s dispensary in Street, Somerset was especially marked by its effective treatment of less severe cases.

Clemens von Pirquet , an Austrian physician, found that patients who had previously received injections of horse serum or smallpox vaccine had faster and more severe reactions to a second injection and coined the word allergy to describe this hypersensitivity reaction.

Soon after, von Pirquet discovered that the same type of reaction occurred in people infected with tuberculosis, and thus discovered the usefulness of what would become the tuberculin skin test.

Individuals with active tuberculosis were generally positive tuberculin, but many of those with rapidly progressive and disseminated disease were negative. This led to the widespread but erroneous belief that tuberculin reactivity is an indicator of immunity to tuberculosis.

Tuberculin dose

In the early 1900s, the tuberculin test consisted of a series of gradual doses of tuberculin. Any reaction at any dose was considered a positive test, and the tests were used extensively to eliminate tuberculosis as a possibility of diagnosis in sick patients.

In the 1920s and 1930s, the decreasing prevalence of tuberculosis resulted in less transmission of infection to younger age groups and tuberculin was suggested as a method to diagnose the infected state rather than the disease.

The use of a series of skin tests with gradual doses of tuberculin was not practical, and in 1941, Furcolow and his colleagues reported that a dose of 0.0001 mg discriminated patients with tuberculosis from others with the greatest accuracy.

This amount of tuberculin was five times the usual initial dose with the gradual regimen and is said to contain 5 tuberculin units (TU).

This dose of 5 tuberculin units has become the standard for tuberculin tests in the United States.

The newly manufactured tuberculin batches are currently bioassayed, and the standard of 5 tuberculin units is the amount of material that produces results equivalent to those produced by 0.0001 mg of purified protein derivative.

Other doses of tuberculin, such as “first concentration” (1 unit of tuberculin) and “second concentration” (250 units of tuberculin) represent the smallest and largest doses of tuberculin that were administered in the abandoned tuberculin test method.

These doses have been commercially available in the past, but are not standardized by bioassay and have no use in tuberculin test diagnostic programs.

What is the method of reading the TB skin test?

“Reading” the skin test means detecting a raised and thickened local area of ​​skin reaction, called induration. Induration is the key element to detect, not redness or bruising.

Skin tests should be read 48-72 hours after the injection when the size of the induration is maximum. Tests read after 72 hours tend to underestimate the size of the induration and are not accurate.

How are the results of the skin test interpreted?

The basis of the skin test reading is the presence or absence and the amount of induration (localized swelling).

The diameter of the induration should be measured transversely (for example, perpendicular) to the long axis of the forearm and should be recorded in millimeters.

The area of ​​induration (palpable, elevated, hardened area) around the injection site is the reaction to tuberculin. It is important to keep in mind that redness is not measured.

A tuberculin reaction is classified as positive depending on the diameter of the induration in conjunction with certain patient-specific risk factors.

In a healthy person whose immune system is normal, induration greater than or equal to 15mm is considered a positive skin test. If there are blisters (vesiculation), the test is also considered positive.

In some groups of people, the test is considered positive if induration of less than 15 mm is present. For example, an induration area of ​​10 mm is considered positive in the following groups:

  • Recent immigrants from areas of high prevalence.
  • Residents and employees of high-risk areas.
  • Drug addicts.
  • Children under 4 years old.
  • Pediatric patients exposed to high risk adults.
  • People who work with mycobacteria in laboratories.

An induration of 5 mm is considered positive for the following groups:

  • People whose immune system is depressed.
  • People infected with HIV
  • People with changes observed on the chest radiograph that are compatible with previous tuberculosis.
  • Recent contacts of people with tuberculosis.
  • People who have received organ transplants

On the other hand, a negative test does not always mean that a person is free of tuberculosis.

People who have been infected with TB may not have a positive skin test (known as a false-negative result) if their immune function is compromised by chronic medical conditions, cancer chemotherapy or AIDS.

In addition, between 10% and 25% of people with newly diagnosed pulmonary tuberculosis will also have a negative result, possibly due to poor immune function, poor nutrition, accompanying viral infection or steroid therapy.

More than 50% of patients with disseminated tuberculosis (spread throughout the body, known as miliary tuberculosis ) will also have a negative TB test.

A person who received a Bacillus Calmette-Guérin (BCG) vaccine (administered in some countries but not in the US) can also have a positive skin reaction to tuberculosis testing against tuberculosis, although this is not always the case.

This is an example of a false positive result. The positive reaction that is due to the vaccine may persist for years.

Those who were vaccinated after the first year of life or who had more than one dose of the vaccine are more likely to have a persistent positive result than those who were vaccinated as babies.

People who are infected with other types of mycobacteria other than Mycobacterium tuberculosis may also have false-positive tuberculosis skin tests.

Side effects

The test usually does not produce side effects.

There is a very slight risk of having a severe reaction to the test, including swelling and redness of the arm, particularly in people who have had tuberculosis or who have been previously infected and in those who have already received the Bacillus Calmette-Guérin vaccine (BCG ).

Allergic reactions are also rare complications.

Live bacteria are not used in the test, so there is no possibility of developing tuberculosis from the test.

Controversy over tuberculin

In the time of Koch, many Germans died of tuberculosis. For that reason, the public reacted euphorically to the discovery of the pathogen since it awoke hopes of a cure.

Until that moment, the only effective remedy for an infectious disease was quinine (for malaria). At the Tenth International Medical Congress held in Berlin in 1890, Koch unexpectedly introduced a cure for tuberculosis, which he called tuberculin.

He did not reveal his composition, which is understandable since it was not the custom to patent medicine; Fenazona is the only exception. The public trusted the famous doctor and reacted with enthusiasm. Koch received the Grand Cross of the Order of the Red Eagle.

The social hygienist Alfred Grotjahn described the arrival of tuberculin in Greifswald:

“Finally the great day arrived for Greifswald in which the Internal Medicine Clinic was going to perform the first inoculations with tuberculin. It was celebrated as the laying of a first stone or the inauguration of a monument. ”

Doctors, nurses and patients dressed in snow white and the director dressed in a black frock coat stood out against a backdrop of laurels: the ceremonial speech of the internist, the execution of the vaccination in selected patients, a thunderous shout of joy for Robert Koch !

Koch tried to obtain money from his discovery, which was carried out against him, since he had carried out his research in a public institution with public money.

He demanded that the Ministry of Culture finance an institute exclusively to produce tuberculin, and calculated the annual benefit at 4.5 million marks. He also hinted that he had received offers from the United States.

At that time, the regulations for testing drugs did not exist yet. According to Koch, he had tested tuberculin on animals, but then he could not produce the guinea pigs that had supposedly been cured.

He was not worried about the fact that people had a much stronger reaction to tuberculin than their lab animals, with fever, joint pains and nausea.

Among other people who tested the tuberculin was his lover and later his wife, Hedwig Freiberg , who was 16 years old at that time. She relates in her memoirs that Koch had told her that she “would possibly get quite sick” but that “she was not likely to die”.

After tuberculin was on the market, articles appeared increasingly in professional journals and in public media with reports of successful treatments, followed by the first reports of deaths.

They were not taken too seriously because, after all, the doctors were experimenting with seriously ill patients. But Rudolf Virchow was able to demonstrate after performing autopsies on the corpses that the tuberculin did not kill the bacteria, and even activated the latent bacteria.

Robert Koch was forced to reveal the composition of his secret cure, so it turned out that he himself did not know exactly what it contained. It was an extract of tuberculosis pathogens in glycerin, and the presence of dead pathogens could also be confirmed.

Koch asked the Minister of Culture of Prussia for permission and went to Egypt, which was interpreted as an attempt to escape from the German public. A heated debate took place in the Prussian parliament in May 1891.

Koch remained convinced of the value of his cure and presented in 1897 a modified form of tuberculin, which proved to be as useless as a therapeutic agent.

This and many other indications suggest that Koch had no intention of committing a “tuberculin swindle”, a common accusation, but that he had deceived himself.

The medical historian Christoph Gradmann has reconstructed how Koch thought that tuberculin worked: the drug did not kill the bacterium but it initiated a necrosis of the tubercular tissue, which, so to speak, “hungry” the tuberculosis pathogen.

This idea was then outside of traditional medical theories, as it still is today. The tuberculin scandal was generally understood as a warning about how not to proceed when medicines are tested.

The introduction of Emil von Behring of his diphtheria antitoxin in 1893 had been preceded by lengthy clinical trials, and serum was slowly introduced into practical use, accompanied by a critical discussion among experts qualified.

Paul Ehrlich also proceeded with remarkable caution in 1909 by introducing the first chemotherapeutic agent produced synthetically against an infectious disease, Salvarsan, as a cure for syphilis.

In 1907, Clemens von Pirquet further developed tuberculin as a test agent for the diagnosis of tuberculosis, but this was his own achievement, independently of any of Robert Koch’s ideas.

The company Meister Lucius & Brüning AG (later Hoechst AG) in Frankfurt / Höchst bought the large surplus stocks of tuberculin and the company began to produce later under the direction of the Koch student, Arnold Libbertz.