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Febrile reactions

those tests that are used with the main objective of diagnosing certain diseases such as: typhoid fever, brucellosis , rickettsiosis … Thus, doctors make use of febrile antigens to detect antibodies in the serum of patients against infectious agents that have invaded the organism.

Thus, the value of the antibodies depends to a great extent on both the type and the course of the disease itself. For the results obtained to be really valuable, two samples must be taken separated by a period of four weeks; in this way the two can be compared.

Types of febrile reactions

Febrile reactions include the following

  • Typhoid O and H : typhoid fever
  • Brucella abortus : Brucellosis
  • Proteus OX 19 : Rickettsiosis
  • Paratifico a and b : Paratyphoid

Typhoid fever (Typhoid O and Typhoid H)

Typhoid fever is a relatively common infectious disease in certain areas of the world, the main symptom of which is an increase in body temperature.

The signs that characterize this disorder are the following, which are repeated in practically 100% of patients: gastroenteritis sweating, diarrhea … Sometimes there is also a small rash of pink spots.

During the first week after infection, patients experience high body temperature, as well as general malaise; headache and cough are also frequent symptoms. As typhoid fever progresses, the fever can reach 40ºC; In addition, there are other signs such as difficulty breathing, red spots on the abdomen, diarrhea and inflammation of the spleen and liver.

If the disease is not diagnosed and treated in time, the complications can be serious , even life threatening in some cases: internal bleeding, intestinal perforation, encephalitis , endocarditis , kidney failure … They can take place in various organs of the body.

Widal reaction

It is known as the Widal reaction to a serological type process that is used to diagnose typhoid, as well as enteric and undulating fever. The reaction is responsible for measuring the value of the serum against a set of known microorganisms.

It is a test that is based on the principle of antigen-antibody agglutination. In it, the presence of antibodies in the body against the OY H antigen is determined. In this way typhoid fever is diagnosed. However, it is important to evaluate the results appropriately depending on the clinical situation of each patient. In general terms, anti-O and anti-H values ​​greater than 1: 160-200 and greater than 1: 50-100 are considered in endemic and non-endemic areas, respectively.

A diagnosis of typhoid fever is given when baseline values ​​are multiplied by four between one and four weeks. However, it is not possible to wait that long until an adequate treatment is established, so the test is considered an entity with determined isolated values.

Sometimes the Widal reaction has led to false positives in non-infectious conditions, such as autoimmune disorders and chronic liver disease. In the same way, false negatives can occur due to the early measurement of antibodies, patients with immunodeficiencies or the use of corticosteroids.

Brucellosis (Brucella abortus)

Brucellosis, also known as Malta fever , is a disease transmitted by animals to people and is caused by bacteria of the genus Brucella. In the vast majority of cases, patients are infected by eating contaminated food, as well as by maintaining direct contact with livestock. Although the disease can occur in any area of ​​the world, it is especially common in certain areas of Southeast Asia, Africa and America.

Patients with brucellosis present with intermittent high fever during the first phase of the disease; high body temperature peaks occur especially in the evening and are accompanied by other signs such as headache , fatigue, and enlarged lymph nodes.

As the disease progresses without establishing the proper treatment, various complications may arise that affect various areas of the body such as the liver, brain, blood, or respiratory system.


The diagnosis of brucellosis is carried out by isolating the microorganisms from tissue cultures such as blood. Thus, serological processes such as febrile reactions only provide a hypothetical diagnosis.

The most common serologic method for diagnosing this disorder is the Huddleson reaction . It is a rapid agglutination reaction in which decreasing amounts of the serum resulting from the investigation are confronted with persistent amounts of antigen. In this way, researchers can precisely observe whether or not agglutination occurs. A suspension of B. abortus antigens with between 3 and 10 percent of germs in phenol is used with the main objective of locating antibodies.

It is important when interpreting the results to take into account the clinical aspects related to the patients themselves. Of course, as with any type of clinical test, there are false positives and negatives.

Rickettsiosis (Proteus 0X-19)

Rickettsiosis is a bacterial disease that is transmitted to humans by certain animals such as inches, ticks and lice . They are intracellular parasites that show high sensitivity and, in addition, it is not usual for them to survive outside the host, except for Coxiella Burnetii, which transmits Q fever, which is highly resistant to both heat and sunlight.

This disorder can be divided into a total of three categories. On the one hand, what is known as typhus, of the epidemic type, and which is transmitted by lice and inches. On the other hand, spotted fever , in which more than thirty different species are involved, the most frequent being mites and inches. And finally, scrub typhus, transmitted by mites.

The incubation period for this disease ranges from one to two weeks. Symptoms that occur in the vast majority of patients are: fever, headache, skin rashes, abdominal pain, cough, and shortness of breath. It is important that when rickettsiosis is suspected, a doctor is consulted for assistance.


When establishing a clinical diagnosis, it is very important to consider the contagious context of the patients: whether or not they have traveled to endemic areas recently, in what professional environment they work, whether or not they have had contact with animals …

Febrile reaction tests

These types of tests consist of a blood test ; It is a relatively common clinical procedure, in which blood is drawn by pricking a certain vein, usually from the patient’s arm. A test carried out by medical professionals, who make use of new and sterile materials to carry it out.

Once the sample is collected, it is sent to the laboratory so that the analysts detect the presence of antibodies in it. These antibodies determine that the body has had some type of contact with different types of microorganisms. The value of the antibody largely depends on two types of factors: the type and stage of the disease.

For reliable test results to be decisive in the diagnosis, two samples should be taken separated by a period of four weeks.

Preparation for the test

There are a number of tips to assess in relation to preparing for a blood test.

  • The patient must go to the test on an empty stomach to avoid the increase in metabolic synthesis.
  • In the hours prior to the analysis, it is convenient to avoid any type of situation that generates stress and nervousness.
  • It is also important to avoid carrying out any type of physical activity before taking a blood sample.
  • Tobacco is also not recommended before taking the test.

Are Febrile Reactions Reliable?

This is one of the most common questions, both among medical personnel and among users. Currently, they are one of the most requested laboratory tests to diagnose certain diseases in which fever is a main symptom.

Well, the truth is that today they are tests that are increasingly in disuse , especially in developed countries. In developing and underdeveloped countries they continue to be widely used because they are quick and cheap diagnostic tests.

Febrile reactions are relatively unreliable tests due to their low sensitivity and specificity; as we have pointed out, sometimes providing both false positives and false negatives.

Another major disadvantage of febrile reactions is that the values ​​must be compared four weeks apart. Thus, in the vast majority of cases you cannot wait for such an amount of time to confirm the diagnosis and establish an adequate treatment for it. And it is that, many of the diseases detected by this type of clinical tests can lead to serious complications.


In short, febrile reactions are diagnostic tests that are increasingly becoming obsolete since there are currently other more reliable ones that allow for definitive diagnoses. Sometimes, an inappropriate use of this type of procedure, as well as an incorrect interpretation of the results, can lead to the establishment of an inappropriate treatment.

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Hello Readers, I am Nikki Bella a Psychology student. I have always been concerned about human behavior and the mental processes that lead us to act and think the way we do. My collaboration as an editor in the psychology area of ​​Well Being Pole has allowed me to investigate further and expand my knowledge in the field of mental health; I have also acquired great knowledge about physical health and well-being, two fundamental bases that are directly related and are part of all mental health.

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