What is the ELISA technique | Diseases and conditions: Medical tests.


ELISA is an acronym that is known by enzyme-linked inmunoabsorción assay (in English enzyme-linked immunosorbent assay). This is a technique of laboratory that was designed by scientists Swedes and Dutch in 1971, which can detect small particles called antigens, which are usually fragments of proteins. Identification is specific, i.e., get that small segments of proteins stand out and can not be confused with each other.
To identify the antigens are molecules with two coupled components: an antibody (which binds to the Antigen specific) and an enzyme (which is activated and designates the Antigen-binding). Before the discovery of the ELISA radioactive molecules instead of enzymes, used to posing an unnecessary added risk in the laboratory and a higher cost.
Thanks to this technique have been able to perform scientific studies in fields such as biology, biochemistry, and medicine. At the hospital it is mainly used to identify germs aggressors who are found in the blood, urine, sputum, etc. The technique soon became widespread with the use of simple and inexpensive equipment that are used still today in many worldwide diagnostic centers.
The different types of ELISA are:
Direct ELISA: is the most basic form of the technique. It consists of collecting a sample study and place it in a well (small bowl) in front of a sample same but contaminated with the germ to study, and another sample which is known that there are no germ. Applies the antibody with the enzyme in three wells and compare the sample to study with the other two.
Indirect ELISA: it is similar to the direct ELISA, but in this case is first added an antibody without enzyme and then one with enzyme. In this way, the signal issued by the enzyme is much more powerful and test is more sensitive.
ELISA sandwich: in this case in the wells first an antibody is added and then the sample, so that antigens are already held in the bottom of the well. Then add the antibody with the enzyme. It is the most effective way of performing the test.
ELISPOT: it is a type of ELISA that allows to know quantitatively Antigen, even identifies the specific number of cells where is located.

When is an ELISA

ELISA he is recommended in all situations in which you want to detect antigens whose existence can be decisive for a diagnosis or to draw conclusions in a scientific study. Some of the most frequent situations where the ELISA is used are:
Diagnosed with HIV: is the first test that is performed to rule out HIV infection. It is a very sensitive test, so virtually all cases detected. However, may cause false positive results, which is usually repeat back an ELISA and confirmed with a Western-Blot.
Detection of antibodies against microorganisms: sometimes the Antigen to study may be another antibody. This situation occurs, for example, in the identification of antibodies against the bacillus of tuberculosis, among others.
Diagnosis of hepatitis B: similar to HIV, the hepatitis B virus can be recognized easily by an ELISA blood.
Detection of fecal germs: some viruses can be detected in feces when they cause diarrhea; the most frequent are the rotavirus. Sometimes not detected the germ itself, they can identify toxins which produces the same, as it is the case with the e. coli
Detection of antigens in urine: is a very useful and simple test to identify germs that cause pneumonia. Respiratory infections bacteria become blood and from there to the urine, so they can be antigens easily identified with an ELISA, which orients the antibiotic treatment directly.

Preparation for an ELISA

If they are going to conduct a study using the ELISA technique, these are issues that you must take into account:
Duration: sample collection usually takes very little time, what it takes to be a blood analysis. It usually takes seconds or minutes. The results are slow quite a bit, usually several days. In emergency situations, you can perform an ELISA and the results in one hour approximately.
Admission: admission is never needed. Sample collection you do at the time. It can also be the case that made you the test during an entry to identify the cause of your illness, but in this case the reason for the income will be your state of health.
Is necessary to be accompanied?: no, just received a puncture when blood sample which must be, and is not usually very painful. You can go to the clinic, only walking or driving, and return the same way.
Drugs: don't need to take any prior medication. It must be said to the doctor all medications you are taking at that time. Some medications can give false negative results of the test, for example if you take antibiotics and want to detect the germ causing the infection.
Food: you can eat normally, you don't have to go on fasting. But if the sample is blood it is frequent to seize the prick of Analytics to measure yourself with other parameters in blood (sugar, cholesterol, etc.), so it is best that you reports or directly stay in fasting if analytics is early.
Clothes: you can wear normal street clothes.
Documents: it is recommended to carry your health card, although most of the times is enough to you to take the wheel with which the doctor sent you proof.
Pregnancy and lactation: this test can be normally in either of the two situations. In fact, it is a test that is usually performed in periodic inspections of pregnancy established.
Contraindications: there are no contraindications. So just rating if it really is worth the test and the results would serve as something.

How an ELISA

The doctor will ask the analysis by ELISA when necessary and is the best diagnostic weapon to study your disease. To make it, first take you the sample on which the ELISA will be held.
According to the site of specimen collection is recommended to adopt one or other measures. For example, if urethral should not urinate in the two hours before; If a sputum it is best to pick it up first thing in the morning, and if it's a blood sample it is best to match a fever peak. But will those details you know the doctor before testing you, so you should not worry.
Once have collected you the sample to study you can make a normal life. While waiting the results you must not be nervous and you must keep your routine. So you know how ELISA we summarize the steps below:
Settles the sample collected in trays with small pools. To the side there will be wells for samples that are known are contaminated and free of antigens known.
Once you have placed the sample are added antibodies that detect antigens if available. At the other end of the antibodies are coupled enzymes.
If it is an indirect ELISA can be added other antibodies that detect previous antibodies; Thus expands the signal.
Is a washing the wells; antibodies that are not linked to antigens are thus eliminated.
A substrate, i.e. a chemical that reacts with enzymes of antibodies that are added. When the metabolites are formed.
Finally, it measures the amount of metabolite that there are different techniques, such as spectrophotometry.

Complications of the ELISA

The complications of the ELISA are virtually non-existent. It is a safe test that does not entail risks for persons who are subjected to it. The only risk is to accept false as positive or negative results, and take wrong steps in this regard.

Results of the ELISA

The results of the ELISA can take several days since the sample is taken for study. To pick them up there to keep another appointment, since the documentation alone can not be interpreted by the patient. In consultation the doctor will be the most appropriate interpretation of the result. If you are admitted shall communicate them yourself during your stay in the hospital, or later if given medical discharge earlier. In case of an emergency consultation can give you the results in less than an hour.
The ELISA is expressed in qualitative values, i.e. is positive or negative. Only the ELISPOT can provide quantitative results, but there is no standard limits for all studies. When the ELISA is positive it means that they have detected antigens in the sample collected, and therefore there are germs present. When it is negative, not have been able to detect antigens and considered that the sample is not contaminated.
Although it proves very effective may provide false positive or false negative results. In situations where the ELISA is critical and radically change the attitude of the doctor, it is usual to test two times in a row, or perform another to ensure the result. It is the case of the testing of HIV: diagnosis is crucial for a person, and that two consecutive ELISA and other equipment are more than it allows to confirm the diagnosis with much more reliability.
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