PCR diagnosis of infections hypersensitive

PCR: ultra-sensitive diagnostics of infections.  Photo from www.sciencephoto.com

PCR — a method of laboratory diagnosis, aimed at identifying the causative agents of infectious diseases. The three-letter option — it is an abbreviation of the name "polymerase chain reaction". Actually, this title and captures the essence of the method, but in order to understand, will have to thoroughly think high-school biology.

But first — a little history. PCR method was developed in 1983 by Cary Myullisom, for which he was awarded the Nobel Prize. Initially, the method was used mainly for scientific purposes, but then making out his promise and effectiveness of the method are to advance in the medical practice.

The literature is very common in a figurative description of PCR is a method by which scientists can find a needle in a haystack, and then build a stack of these needles. In principle, a very accurate description. If we continue the comparison, the needle — a small portion of the genetic material of a microorganism, and a haystack — it's the human body, in which the organism is settled.


For the genetic information in the living body of any size corresponds DNA — deoxyribonucleic acid double-stranded, consisting of a sequence of four nucleotides which are usually denoted by the letters A (adenine), G (guanine), T (thymidine) and C (cytosine). One of the basic rules of genetics — the rule of complementarity, ie the nucleotides adjacent helices are connected only in a particular order: A with T, G with C, and nothing else.

Every living creature (a bacterium, a virus, a fish, a beast) — has its own DNA, and to identify the specific organism is sufficient to have only a small area of the storage of genetic information. Some types of microorganisms, e.g., human immunodeficiency virus, the genetic information stored in the other nucleic acid — RNA, but also fragments thereof can be found by PCR.

It is on the discovery of this small but unique to each individual body size and built the principle of PCR. For each set a specific pathogen genetic detector reference DNA fragment, which accurately detects complementarity principle 'own' DNA fragment and the reaction starts creating large numbers of copies thereof.

One PCR cycle lasts about three minutes, the number of copies increases exponentially. Thus, in a few hours the number of fragments increases by several billion times. It is understood that it is now to determine which of the pathogen from a specific infection, rather easy.


Theory — it is certainly great, but what we have on the output? What practical benefit a person receives when goes in search of harmful microorganisms, armed with PCR?

  • Of course, one of the main advantages — it versatility method. PCR can detect any DNA and RNA, even when other methods powerless. The equipment used for the PCR standard, it does not depend on what it is and where it is we're looking for.
  • Another advantage — high specificity. In the material sent for analysis, defined a unique sequence of nucleotides that are unique to a particular pathogen. Thus, we can say that the specificity of 100%. Additionally, it allows at the same time in one and the same material, to conduct a search without pathogens a compromising the quality of the answer.
  • PCR has the highest sensitivity — We are already talking about what's possible to find just one piece of genetic material pathogen.
  • The definite advantage of the method — efficiency. Statement of the reaction takes several hours, so that all the diagnostics, from the moment of delivery of the material for analysis to obtain a result, takes only one day.
  • Using PCR identify the causative agent, not reacted at its introduction from the body. Thus, it is possible to accurately diagnose the disease still in the incubation period, when there is no clinical or laboratory signs of the disease.


Of course, the PCR method is not perfect, there are also disadvantages. But they are directly related to his virtues and the so-called "human factor". PCR — very high-tech method, requiring the strictest rules of the laboratories. Suffice it to say that the space filter should be set with a degree of biological purification of 99.9%. This is due to the fact that the air is always present incredible cocktail of DNA fragments of various living organisms, and in preparation for the reaction, the sample may be contaminated — perhaps "false alarm."

Evaluate the results of the PCR should practitioner who is treating a particular patient. The fact is that not always PCR positive response indicates the presence of disease. For example, a man was treated bya disease, but the victim and is not dangerous exciter will still take some time "to understand parts" defense system. If at this point to make PCR — the result will be positive.

Another option — a negative PCR result, even if explicit clinical picture. One of the possible causes — the material for the study was taken "not there." The sample should take a qualified doctor, strictly following the instructions, which he gives the laboratory.

When should you do?

When should I run to the lab to analyze the results of your summer vacation? Experts advise to do it in the following cases: discharge, itching, burning sensation in the genital area, dramatically changed the smell of genital discomfort when urinating, an unusual pattern of secretion (color, quantity, consistency), casual sex without using a condom.

Of course, the PCR — a powerful and effective diagnostic tool that can quickly and accurately find the causative agents of many diseases. Most often it is used to diagnose disease is transmitted through sexual contact. And often the clinics and labs are ready to offer a kind of "sets" — 5 infections, 13 infections.

In any case, not limited to a single method. It is best to combine different methods of investigation — besides determination of the pathogen by PCR to assess the immune response of the organism and which is determined by conventional serological methods such as ELISA.

And remember: a positive response in even the most modern laboratory research — it's not a reason to panic, but to visit a doctor.

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