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Analyzes of lamblia: interpretation
Last reviewed: 19.10.2021
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Suspicion of parasite infestation occurs when there are persistent dyspeptic disorders. Giardiasis is a protozoal infection caused by the smallest intestinal parasites of Giardia or Giardia. The disease is well researched, modern methods of its treatment give a 100% cure effect. The main thing is the timely diagnosis of infection by these parasites, and the physician can learn the basic information from the results of laboratory tests for the presence of a lambliosis patient.
[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]
Preparation for analysis on Giardia
The negative result of research does not at all mean that there are no parasites. Analyzes for the presence of lamblia are usually taken repeatedly. Often in a dubious result the patient himself is guilty. Observance of several simple rules before passing the analysis will make the research results more accurate. Therefore, how to take the analysis for Giardia, so as not to waste time?
Intending to take the tests, you need to stop taking anthelmintics at least seven days before the scheduled time, as well as drugs that can harm parasites: antibacterial (metronidazole, trichloropol), antacid (smect). It is advisable, if possible, not to take any medications at all.
A blood test for antibodies to lamblia (enzyme immunoassay) is given on an empty stomach in the morning from a vein. Before taking blood for 10 hours, it is necessary to stop eating food and any beverages, except for pure still water.
Cal for analysis is collected from the liquid fraction in six to seven places and is sealed in a sterile container with a sealed cap. It is desirable to collect it in the morning and deliver it to the laboratory as quickly as possible within two hours. If you deliver feces in 20 minutes, then in this case, the laboratory assistant will be able to detect vegetative forms of parasites. Within 12 hours - formed by them cysts. Longer delivery times reduce the informative value of the analysis. However, often the medical staff requires that warm feces be delivered to the analysis. This requirement to perform is problematic and it is illegal, from the moment of defecation to the receipt of analysis by the laboratory should take no more than 12 hours. You can ask for a container in the laboratory with a preservative that will extend the shelf life of the material.
Feces on the antigen are collected in a sterile container, preferably immediately delivered to the laboratory. If this is not possible, the container can be stored, keeping the temperature 2-4 ° C (in the refrigerator) one or two days. A single deep freeze (-20 ° C) is also permissible, if longer storage is assumed. The material for the study is collected within the first week of the onset of clinical symptoms.
On the question "Where to pass the analysis on ljamblii?" - the doctor who will write out a direction on the analysis most simply answers. Such an analysis is done in all laboratories of polyclinics, hospitals and in commercial laboratories.
More patients often wonder: how much is the analysis prepared for lamblia? Stool analysis is prepared quickly enough as soon as the sample reaches the microscope. It's just that the result should be formalized, usually it is ready in the second half of the day of the analysis.
A blood test for antibodies to lamblia will be ready in two days, feces for antigen - every other day. The result of PCR analysis on lamblia is ready in 4-6 hours.
Comparative effectiveness of diagnostic methods
The analysis of blood for antibodies to lamblia is an indirect diagnostic method, since they are formed in the blood as an immune response to parasitic infestation. Appear not immediately, but for two, and sometimes three weeks, so in the first days after infection, the result will be false-negative. The presence of class M immunoglobulins indicates a recent infection, but they do not last long and are replaced by IgG, the presence of which confirms that the invasion was. But they can last a long time after recovery and do not indicate the need for treatment, and therefore are not suitable for monitoring its effectiveness.
The indicator of the presence of antibodies depends on many factors, in particular, the state of the immune system and the intensity of infection. With low immunity or chronic recurrent lambliasis with persistent flow, antibodies can not be detected. There are also false-positive results of the analysis in case of invasion of other protozoa, for example, amebiasis, antibodies to which can be mistaken for antibodies to lamblia.
The analysis of feces on Giardia is more reliable. It consists in studying a sample of feces taken from several places, under a microscope and a visual search for living individuals or their cysts. If the result is positive, then the parasites are definitely there. A negative result does not mean that the patient is healthy. Simply in the development of parasites, there are so-called "blind" periods, their duration is 1-17 days, in which cyst development does not occur. If the analysis is collected and delivered exactly during this period, the result will be negative even if there are parasites. Therefore, it is recommended to take an analysis of feces for lamblia cysts at least three times every three days. If the suspicion of the presence of parasites is serious, then the feces are monitored for a month or one and a half, every week.
The two above-described blood and stool tests are most often used, as most laboratories do. Usually, a study is ordered, both blood and feces. If one of the tests is positive, then we can conclude that there is an invasion.
The analysis for lamblia antigen is more informative than feces microscopy, but its availability is limited, as it is done only in large cities and not all commercial laboratories. The study of the material is based on a one-stage immunochromatographic method, which makes it possible to detect specific molecules (GSA-65 antigens) that are found exclusively in lamblias. Samples of feces are mainly taken for the study, but a biopsy specimen is sometimes used. The immunochromatographic method makes it possible to detect lamblia even in the "blind" period. It is advisable to use it to monitor the recovery, but after a two-week interval after the withdrawal of the drugs, since the antigen can still be released in this time interval.
To identify parasites, the most informative at present is the analysis of PCR on lamblia. Its main drawback is the lack of prevalence. It is not done practically in any laboratory, even in large cities. This study allows, using the polymerase chain reaction, to determine in the feces fragments of lamblia deoxyribonuclease even in the interval when the cysts are not secreted. The accuracy of this analysis is the highest (up to 98%).
Interpretation of the values of the analysis on Giardia
The results obtained in the determination of serum antibodies to lamblia are compared with the reference indices. The lower limit of the norm of preserving the activity of antibodies is fixed in the proportion 1: 100. The activity of immunoglobulins less than 1: 100 is estimated as a negative result. With an activity exceeding this ratio, a conclusion is drawn about the presence of giardiasis. The antibody titer exactly 1: 100 is interpreted as ambiguous. The analysis is recommended to be repeated, as well as the analysis of feces for lamblia cysts.
The IgM positivity coefficient is greater than 1 and less than 2, which speaks of the level of antibody concentration in the blood serum, in combination with the absence of IgG, is diagnosed as the initial stage of giardiasis.
The positive factor of immunoglobulin class M equal to two in combination with the detection of cysts in microscopy of feces is usually interpreted as an acute lambliasis.
When cysts are detected in the analysis of stool, absence of IgM, and the level of IgG concentration equal to 1-2, chronic lambliasis is diagnosed.
Positive analysis for the definition of IgG causes doubts in the unambiguous presence of lamblia in the body, since the G-class immunoglobulin is determined in the blood serum for another six months after the cure.
Norms of analysis of feces on Giardia - the absence of any form of parasites. In the presence of living individuals or their cysts, the analysis is considered positive.
The negative result of analysis of stool for lamblia antigen should be very likely to indicate their absence. However, it can be with a small number of cysts in the feces, while a second study can produce a positive result. Therefore, if there are clinical manifestations, the analysis is repeated. A positive result indicates infection or carriage.
Analysis of PCR on Giardia can be positive in determining the DNA of these parasites in biological material and negative in their absence.
None of the above analyzes in itself does not give 100% of the result, so a diagnostic interpretation is built up with a comprehensive analysis of all available survey data.