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PCR (polymerase chain reaction) | Diseases and conditions: Medical tests.


What is PCR

PCR is an acronym that is known to the polymerase chain reaction (English Polymerase Chain Reaction), an advanced scientific technique which was invented by the American biochemist Kary Mullis in 1985. This technique allows to amplify small specific regions of DNA in the laboratory. That is, get a small segment of DNA that would go unnoticed in any analysis is multiplied millions of times and is thus easy to detect.
Thanks to this technique have been able to be genetic studies in any field of science. For example, used daily for the identification of dead bodies or in the study of crime scenes to look for traces of the culprit. Also used in biology, to identify genetic chain of plants, animals or, above all, microorganisms. In medicine meets the experience of all those camps and is mainly used to identify aggressors germs found in our body.
When the PCR test was developed for the first time was a rather cumbersome and expensive technique to perform, but soon their use became widespread, and began to develop simple and very cheap computers that are used still today in many diagnostic centers.
Also, are designed more specific PCR can be chosen depending on the sample to study. The different types of PCR, in addition to the Basic, are:
Nested PCR: get amplify minimum samples of DNA to billions of fragments. It is therefore capable of detecting tiny strokes.
PCR in situ: allows the detection of DNA in the same place of the exhibition, without having to process it first with laboratory techniques. It is typically used for biopsies or cell.
Multiple PCR: this type of PCR are available to detect multiple traces of DNA at the same time and with a single sample.
With reverse transcriptase PCR: in this case, chains of RNA are used to detect DNA moulds. Transcriptase enzyme used reverse, the same used by HIV among other viruses.
Quantitative PCR or real-time PCR: added a fluorescent component that allows to measure light. More light, more quantity detected DNA.

When a PCR is made

It is recommended to perform a PCR in all situations in which you want to detect DNA chains and amplify it, either to perform studies on it or to identify their exact sequence. As for example, in the following:
Microbiological diagnosis: the most reliable method to identify a germ is isolated in a microbiological culture, but sometimes it is not possible to carry it out, either because the method of cultivation is difficult or because it is too expensive. In those cases the PCR can detect genetic material of the micro-organism that is necessary to detect. The sample collection can be of any type:
· Blood.
· Swab exudate.
· Vaginal exudate.
· Rectal exudate or stools.
· Urethral discharge or urine.
· Biopsy (skin, bone marrow, liver, etc).
· Sputum.
Detection of genetic mutations: genetic diseases are caused by a focal mutation in a specific region of DNA. It is very difficult to study them directly, so you opt for first multiply all the DNA sample and conducting studies with more broad-based. Thus confirms the diagnosis of many diseases like cystic fibrosis, the Chorea Huntington, Rendu-Osler-Weber disease, etc.
Studies of legal medicine: its use is widespread in this field and has many applications. The most common are the identification of corpses, the study of evidence from scenes of crime, investigation of cases of sexual abuse, paternity studies, etc. All of them are based on the amplification of DNA to study their sequence with ease.
Reviews of HIV or viral hepatitis: HIV and hepatitis B and C viruses are constantly in the blood of infected people. Your levels should periodically be reviewed to know the severity of the disease and the detection of DNA with PCR.a is used to do this

Preparation for PCR

If they are going to conduct a study with PCR these are the issues you should keep in mind to go well prepared to test:
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.
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 that causes infection.
Food: you can eat normally, you don't have to go on fasting. But if the sample is blood is common to seize the prick of Analytics to measure yourself with other parameters in blood (sugar, cholesterol, etc.), so the best thing is 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, though most of the times is sufficient that you carry 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. Just have to assess if it is really worth the test, and if the results would serve something.

How a PCR

When you get to the consultation the doctor will make you some general questions about your state of health: important diseases, risk factors, lifestyle, symptoms of infection, etc. The doctor will ask the PCR assay where deemed necessary and is the best diagnostic weapon to study your disease. After perform you a general physical examination, and assess if you can receive a mobile treatment or prefer that you stay logged.
After this first visit, they will take you the sample on which the PCR will be held. According to the site's collection of taking one or other measures are recommended. For example, if urethral should not urinate in the two hours before; If it is a best sputum that is first thing in the morning; and if it is better blood that matches a fever peak. But will those details you know the doctor before testing you, so you should not worry. If they are studying genetic disease usually they will make you a skin biopsy.
Once have collected you the sample to study you can lead a normal life. While waiting the results you must not be nervous and you must keep your routine. The study of PCR is performed in the laboratory, and you won't be aware of none of the steps of the technique. So that you know them, we summarize them here:
1. is extracted from the sample collected DNA that contains. This includes your own body cells, but also material of any germ that has.
2. the sample is heated up to nearly 100 ° C so that the two strands of DNA are separated.
3. added to sample a choke; This is a sequence of DNA synthesized in the own laboratory which is attached to a known DNA. For example, if we want to detect Cytomegalovirus we will use a specific Primer for it.
4. the sample is cooled so that the choke is a DNA studied. He then starts an enzyme called DNA-polymerase, which doubles the DNA to study.
5. repeat all the previous steps; whenever you finish a cycle will provide a duplication of the previous strands of DNA.
6. with the already amplified DNA genetic studies of quickly and easily can be.

Complications of the PCR

Complications of the PCR 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. The sample does not usually entail risks, except those of the biopsies as the organ which will take.

Results of the PCR

The PCR results They may take several weeks since the sample is collected 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.
The PCR is expressed in numeric values, but there is no standard limits for all studies. Each goal has own values, so that a PCR for Cytomegalovirus of 100 does not have the same value that a PCR of Chlamydia from 100.
The result of the PCR usually can be summarized in positive or negative. I.e. the DNA that we expected, or not found. That is essential in order to identify specific germs and provide a specific antibiotic, or to diagnose a genetic disease and measure the amount of mutated DNA.
Although it is a very effective test can provide false positives. It must be borne in mind that the choke can adhere to the DNA that we want to detect, but also binds by pure chance to other strands of DNA that are close. False negatives are rare, since narrowly DNA that is usually detected.
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