A Blood Test For Toxoplasmosis: When Is It Prescribed And How To Donate

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A Blood Test For Toxoplasmosis: When Is It Prescribed And How To Donate
A Blood Test For Toxoplasmosis: When Is It Prescribed And How To Donate

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The analysis for toxoplasmosis is especially important during pregnancy, as this disease can cause significant damage to the health of the unborn child. The presence or absence of toxoplasmosis in the blood is determined by immunological or serological methods, in some cases instrumental diagnostics is possible.

The content of the article:

  • 1 What is toxoplasmosis
  • 2 Causes of toxoplasmosis
  • 3 Diagnosis of toxoplasmosis
  • 4 Toxoplasmosis in adults
  • 5 Acute acquired toxoplasmosis
  • 6 Chronic toxoplasmosis
  • 7 Latent toxoplasmosis
  • 8 Laboratory diagnostics of toxoplasmosis when donating blood
  • 9 Decoding of tests for toxoplasmosis

    • 9.1 Blood test for IgG and IgM antibodies. IgG antibody avidity
    • 9.2 Antibodies of the IgM type against Toxoplasma
    • 9.3 Antibodies of type IgG against Toxoplasma
  • 10 What does the avidity (avidity index) of IgG antibodies against toxoplasmosis mean?
  • 11 How to get tested for toxoplasmosis

What is toxoplasmosis

Toxoplasmosis is a protozoal invasion, characterized by a wide variety of course variants and polymorphism of clinical manifestations.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

In 1972, WHO experts included toxoplasmosis among the zoonoses most dangerous to human health, and later, due to the spread of HIV infection, it was recognized as one of the few opportunistic infections of protozoal etiology.

Toxoplasmotic invasion is widespread, almost ubiquitous: on the globe, from 500 million to 1.5 billion people are infected with Toxoplasma. The prevalence of the population in different countries depends on sanitary and hygienic conditions, dietary habits, the influence of environmental factors, the frequency of immunodeficiency states, etc.

Infection rates of the population in various regions of Russia range from 15 to 50%, and the incidence of congenital toxoplasmosis among newborns averages 3-8 children per 1000 births.

The source of the causative agent of the invasion is the domestic cat and many species of wild and domestic animals. However, cats excrete oocysts with feces for a short period (1-2 weeks) and only at the age of 4-5 months, therefore, infection directly from the cat - the final host of the pathogen - rarely occurs (for example, infection of a child by contact with cat feces in a sandbox and non-compliance with hygiene rules).

Blood test for toxoplasmosis
Blood test for toxoplasmosis

Infection of people occurs in various ways: alimentary, contact, congenital (transplacental), parenteral, infection of medical personnel in contact with blood is possible.

Often people become infected by eating foods from the meat of intermediate hosts that have not undergone sufficient heat treatment (grilled chicken, shawarma, shashlik, raw minced meat), poorly washed vegetables, etc. Depending on the mechanism of infection, a distinction is made between acquired and congenital toxoplasmosis.

Causes of toxoplasmosis

It causes the disease toxoplasma, which is the simplest microorganism and lives in cells. In other words, Toxoplasma is an intracellular parasite.

The final carrier of Toxoplasma is cats, as well as some other representatives of the feline family, and the intermediate carrier is humans, birds, less often some mammals (farm animals, dogs).

There are several ways of human infection:

  • through the digestive tract (for example, through contact with contaminated soil, with cat feces, when eating unwashed vegetables and fruits, poorly cooked or cooked meat, and possibly cow's milk);
  • transmissible or through blood (contact with infected meat in the presence of cuts and abrasions on the hands, through the saliva of infected dogs when they lick their wounds, less often - during blood transfusions and organ transplants);
  • vertical (from mother to fetus through the placenta) if a woman is infected with toxoplasmosis during pregnancy.

Diagnosis of toxoplasmosis

To diagnose toxoplasmosis in children and adults, patients are assigned a whole range of studies. In this case, it may be necessary to conduct an examination of the fundus, ECG, EEG, CT, X-ray of the skull, assessment of the degree of muscle damage, etc.

The clinical signs of toxoplasmosis are a stable increase in temperature up to 37.5 ° C, an increase in lymph nodes, liver and spleen, damage to the main organ of vision, and the formation of calcifications in brain tissues.

The data for making a diagnosis allow you to obtain: anamnesis collected in each individual case; external examination of the patient; laboratory research; instrumental diagnostic methods.

As laboratory tests, as a rule, ELISA and PCR are prescribed. To determine the presence of specific antibodies in the patient's body, RPHA, RSK, etc. are prescribed. Early diagnosis of toxoplasmosis during pregnancy is the most important for maintaining the health of the fetus and the expectant mother herself.

To determine the disease, the placenta, amniotic fluid, membrane are examined for the presence of Toxoplasma DNA. When diagnosing toxoplasmosis, it is important for specialists to distinguish its signs from the symptoms of lymphogranulomatosis, rheumatism, tuberculosis, herpes infection, infectious mononucleosis.

There are the following types of toxoplasmosis diagnostics:

  • immunological and serological. They are based precisely on the characteristics of the body to produce antibodies to infection. Using special test systems, the presence or absence of IgG and IgM immunoglobulins is determined. Thus, it is possible not only to detect the presence of protective antibodies in the body, but also to timely diagnose the acute phase of toxoplasmosis. Is a toxoplasmosis blood test scheduled? The norm is the detection of IgG antibodies and the absence of IgM. Methods for direct detection of the parasite - studies using microscopy or PCR diagnostics;
  • instrumental methods are used only in complicated and controversial cases. Apply ultrasound, computer examination and others;
  • a biological sample can also indicate the presence of IgG immunoglobulins in the body. After subcutaneous administration of a special allergenic preparation, the reaction is monitored for two days. When puffiness appears, a positive result is recorded.

Toxoplasmosis in adults

At any age, a disease such as toxoplasmosis can develop in adults.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

Toxoplasmosis in adults can cause various morphological manifestations. Microscopic examination performed can determine the presence of a large number of miliary granulomas contained in the brain as well as in the spinal cord. Such granulomas can consist of lymphocytes, epithelial cells, monocytes, and often of eosinophils.

Every person who comes into contact with animals of the feline family or with their waste products, who eats animal products that have not undergone appropriate heat treatment, etc., is susceptible to parasite infection.

The degree of damage to the body by toxoplasmosis in adults, as in children, depends on the state of the immune system. So, in most of the people who have Toxoplasma in their bodies, clinical manifestations of the disease are not observed. However, a sluggish process of development of chronic toxoplasmosis in adults is also possible, and quite rarely - an acute form of the disease with a severe course.

Acute acquired toxoplasmosis

Acute forms of the disease are rarely recognized. First, Toxoplasma enters the regional lymph nodes, where they cause hyperplasia (enlargement). The lymph nodes are soft to the touch, they are welded to the surrounding tissues and are painless.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

The occurrence of a roseolous-papular rash (in the form of nodules and inflammatory spots), as well as an enlargement of the liver and spleen (hepatosplenomegaly), is most often affected.

From the lymphatic system, Toxoplasma penetrates the bloodstream and is carried to organs. With brain damage, there is a different neurological clinical picture (movement and visual disorders, impaired sensitivity, dizziness).

If the posterior columns of the spinal cord are affected, pulling pain occurs with accidental movement along the nerves. In the case of involvement of peripheral nerves, pain and numbness of the arms and legs along the nerves, changes in pain sensitivity are observed.

Cerebral symptoms are observed with entephalitis, meningoencephalitis and ependymoencephalitis (these conditions can develop against the background of toxoplasmosis). The meninges are involved in the pathological process, which leads to their inflammation and an increase in intracranial pressure.

In these cases, the following characteristic symptoms occur: tension in the occipital muscles; difficulty bending your head to your chest; vomiting, accompanied by a headache and not bringing relief. At the same time, complaints of headaches are usually diffuse, diffuse in nature.

These symptoms often lead the doctor to suspect a brain tumor. Vascular crises, mental instability with character changes can be added to the listed manifestations.

Chronic toxoplasmosis

Chronic toxoplasmosis can be primary or secondary. This disease is characterized by a sluggish, long-term non-manifesting course, accompanied by a change in periods of exacerbations and remissions.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

In this case, the primary symptoms of the disease are general intoxication of the body, a persistent increase in body temperature to 37.5 ° C, as well as myalgia and arthralgia. People diagnosed with chronic toxoplasmosis may experience unreasonable irritability, memory impairment, and neurotic reactions.

Widespread enlargement of lymph nodes and digestive disorders (bloating and aching pains, nausea and constipation) are also not uncommon in chronic toxoplasmosis.

Other signs of the disease of this form include: the development of specific myositis and myocarditis; symptoms of VSD (vegetative-vascular dystonia); disturbances in the endocrine system; violations of visual function (uveitis, chorioretinitis, retinitis).

In addition, in a laboratory study of peripheral blood in patients with chronic toxoplasmosis, leukopenia, lymphocytosis, and neutropenia may occur. There may also be a tendency towards eosinophilia. In this case, ESR indicators may be normal.

Latent toxoplasmosis

Chronic toxoplasmosis of the latent form is characterized by the absence of any of its symptoms. It is possible to determine this form of the disease only when conducting appropriate laboratory tests.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

Most often, primary-latent toxoplasmosis occurs, much less often - secondary-latent. The main danger of latent and chronic toxoplasmosis lies in the relative likelihood of its transition to a severe generalized form.

The development of such a complication is possible in the presence of HIV infection and other diseases in the body that provoke immunodeficiencies.

Toxoplasmosis in HIV-positive patients, as well as people diagnosed with AIDS, most often leads to the development of meningoencephalitis and brain abscesses. During the development of the disease, damage to the heart, myocardium, lungs and other organs and systems of the body is also possible.

Laboratory diagnostics of toxoplasmosis when donating blood

The most effective and simple way to determine diseases of an infectious and inflammatory nature is a serological diagnostic method. In this case, the analysis for toxoplasmosis is performed by drawing blood from a vein.

In the process of research, the material is damaged by centrifugation, which makes it possible to isolate serum from the total mass of blood.

The second way to test for toxoplasmosis is the allergological method. In this case, 0.1 ml of toxoplasmin is injected intradermally outside the shoulder to the patient. A positive reaction of such an analysis to toxoplasmosis is expressed in redness or the formation of an infiltrate in the area of ​​administration of the substance.

The study of blood serum is aimed at: detecting IgM in it, indicating the course of an acute inflammatory process; determination of IgG, the presence of which indicates that the process has already been transferred. In modern medical practice, the use of complement binding seroreaction, Sebin-Feldman, immunofluorescence, better known as RIF, and enzyme-linked immunosorbent assay (ELISA) are relevant.

Reactions to an allergy study can be different: sharply positive - the diameter of the intradermal reaction reaches 2 cm or more; positive - the size of the reaction is 13-20 mm; slightly positive - the diameter of redness is 10-13 mm; negative - the reaction size is less than 9 mm.

The third laboratory method for determining toxoplasma in the body is a parasitological research method. Such an analysis for toxoplasmosis is aimed directly at identifying the causative agent of the disease in the composition of body fluids and tissues. In the first case, blood, amniotic fluid or cerebrospinal fluid can be used, in the second, tissue taken from a lymph node biopsy.

Decoding tests for toxoplasmosis

If you have already passed the tests for toxoplasmosis and received the results, carefully study the form that was given to you in the laboratory and select from the points below the item that contains designations or abbreviations similar to those on your form.

Blood test for IgG and IgM antibodies. IgG antibody avidity

In order to determine whether a person has ever been infected with toxoplasmosis, and if so, how long ago it happened, doctors often prescribe blood tests (from a vein) that can detect antibodies against certain Toxoplasma antigens. Below we will explain what this means.

When these substances (antigens) enter the blood of a person, the cells of the immune system recognize them as foreign and begin to develop antibodies against them (syn. Immunoglobulins), which accumulate in the blood at certain concentrations (titers).

Since different laboratories use different analytical methods, the values ​​of "normal" and "elevated" antibody titers (indicators) depend on which laboratory the analysis was performed in.

Like any other microbes, Toxoplasma is composed of complex organic matter. These substances are called antigens.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

For this reason, as a rule, in the forms with the test results that are issued in the laboratory, in brackets, next to the analysis result, the "normal" value of the antibody titer is indicated in comparison with which the antibody titer detected in a person can be said to be increased or decreased.

If the antibody titer is higher than normal, the result is considered positive. If the antibody titer is below or within the normal range, or if there are no antibodies of this type at all, the result is considered negative.

Positive and negative titles (indicators) can also be marked with a special inscription or stamp (for example POZ - for positive and NEG for negative).

IgM antibodies against toxoplasma

Blood test for toxoplasmosis
Blood test for toxoplasmosis

IgM are antibodies that the immune system begins to produce 1 week after a person first becomes infected with toxoplasmosis. Thus, the appearance of antibodies of this type in a person's blood may be one of the very first signs that he has contracted this infection.

The human immune system is designed in such a way that antibodies of the IgM type are produced only at the very beginning of the disease and disappear when several months have passed since the onset of the disease. Only a few people retain a positive IgM titer for a long time (up to 18 months) after infection.

The association of a positive IgM titer with recent toxoplasmosis infection is especially likely if a parallel IgG antibody test is negative or if IgG with low avidity was detected (see below).

If you have a positive (elevated) IgM antibody titer against Toxoplasma, it may mean that you have recently been infected with this infection (several weeks or several months ago).

IgM tests can be wrong, so in cases where a person tests positive, they are usually prescribed additional tests to determine whether they have actually been infected with toxoplasmosis recently.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

In particular, the doctor may order you to retest for IgG and IgM antibodies in 2-3 weeks. If the antibody titers are the same as on the first test, this will be a strong argument in favor of the fact that you have not been infected with toxoplasmosis recently and that the IgM test gave a false positive result.

If the result is IgM negative, this is a strong argument in favor of the fact that you have not been in contact with toxoplasmosis in the past few months.

IgG antibodies against toxoplasma

IgG are antibodies that begin to be produced by the immune system a few weeks after infection with toxoplasmosis, but which, unlike antibodies of the IgM type, do not disappear, but rather accumulate in the blood and remain in it, at a certain concentration, throughout a person's life.

If a blood test determines that your blood contains a positive (increased) titer of IgG antibodies against Toxoplasma, but there are no IgM antibodies (negative result), this will mean that you have been in contact with toxoplasmosis in the past and have some immunity against this disease.

What does the avidity (avidity index) of IgG antibodies against toxoplasmosis mean?

In medicine, the term "avidity" is used to refer to how strongly antibodies can bind to the microbe against which they were developed. The term high avidity means that antibodies can bind strongly to the microbe, and the term low avidity means that antibodies do not bind very strongly to the microbe.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

The human immune system is designed in such a way that at the very beginning of infection, it produces antibodies with low avidity and a few months after contact with a microbe begins to produce antibodies with high avidity. Low avidity antibodies gradually disappear from the blood, while high avidity antibodies remain in the blood for a long time (possibly for life).

If IgG antibodies with low avidity are found in your blood, this means that you have contracted toxoplasmosis within the last few months.

Thanks to this phenomenon, by measuring the avidity of antibodies using special biochemical tests, doctors can determine how long ago a person was infected with one or another infection. If IgG antibodies with high avidity to Toxoplasma have been found in your blood, this may mean that you have been infected with this microbe in the past.

How to get tested for toxoplasmosis

Blood for PCR and ELISA for the detection of toxoplasmosis is given in exactly the same way. During the day preceding the donation of blood for toxoplasmosis, you should refrain from consuming large amounts of lard, oil, meat, alcoholic beverages, as this can lead to a change in the quality of the whey.

Blood test for toxoplasmosis
Blood test for toxoplasmosis

If the serum is chyle, then the test result for toxoplasmosis cannot be considered accurate. In addition, you do not need to take blood-thinning drugs (for example, Aspirin, Heparin, Thrombostop, etc.) on the eve of the test, as this increases the risk of hemolysis. Hemolyzed blood cannot be used for the production of an analysis, since its accuracy and information content is extremely low.

If the donated blood turns out to be hemolyzed, or the serum obtained from it is chyle, then the analysis will have to be redone. No special preparations for donating blood for toxoplasmosis are required. Blood for toxoplasmosis is donated from the cubital vein.

If it is impossible to perform venipuncture in this area and obtain the required amount of blood for research, then it is taken from other vessels, for example, on the back of the hands or feet, etc. Venous blood for toxoplasmosis is collected according to the usual routine procedure.

Blood from a vein for toxoplasmosis testing can be donated at any time of the day. That is, the time of day at which blood was taken for toxoplasmosis does not affect the results of the study. However, in most laboratories, blood sampling for research is carried out in the morning, so you will have to obey the accepted routine.

Find out more:

  • Toxoplasmosis in humans: signs, symptoms and treatment
  • Toxoplasmosis - symptoms and treatment methods for the disease
  • Analysis for toxoplasmosis: why and how to take it right
  • Toxoplasmosis in women: causes, symptoms and treatment
  • Toxoplasmosis - treatment with medicines and folk remedies

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