What is a blood test for PCR, and why is it needed?
Diagnosis of infectious diseases - bacterial and viral - is aimed at early detection of pathogens, which allows you to prescribe early and most effective therapy.The most modern way of diagnosing infections is PCR or polymerase chain reaction.So what is this method, and what is it for?
The essence of the polymerase reaction
Any microorganism and virus contain in their structure a DNA or RNA molecule.Each of these compounds is unique, therefore, if you select nucleic acids in a blood test in children or adults, you can diagnose with absolute accuracy.
Unfortunately, the concentration of DNA in blood samples or other biological materials is low enough and it can not be determined using conventional diagnostic methods.To cope with this problem, a polymerase chain reaction was invented.
The essence of PCR is the special processing of the blood sample, as a result of which the concentration of DNA molecules increases, the determination of which in the future makes it possible to establish the type of pathogen and to diagnose it.
How to donate blood to PCR
When preparing for the analysis, one should adhere to the general recommendations: do not drink or eat immediately before the blood test.Although it is possible to strictly adhere to these requirements so that the blood can not be delivered to the PCR, as the accuracy of the test does not depend on whether the assayed or empty stomach was taken.
What diseases can be detected using PCR
With PCR, you can identify virtually any viral and bacterial diseases.For the analysis, not only blood but also other biological materials are used: sperm, saliva, smears from the urethra and from the cervix.A blood test will be informative if the causative agent of a particular disease enters the blood of a person. Therefore, PCR is prescribed for the following diseases:
- viral hepatitis A, B, C, D and TT;
- herpetic infection( herpes viruses 1, 2 and 4 types);
- HIV infection
- Enterovirus infection;
- herpes zoster;
- infectious mononucleosis;
If we take into account the possibility of carrying out PCR of other biomaterials, then the following diseases should be added to the list of diseases detected by PCR:
- papillomavirus infection( of the order of 100 different strains of the human papillomavirus);
Particularly relevant at present, the PCR analysis of the pregnant woman's blood on the so-called TORCH infections: cytomegalovirus, toxoplasmosis, rubella and herpesvirus infection.This is due to the fact that these diseases can lead to fetal development anomalies.
Advantages of PCR
- 100% accuracy of diagnosis - if there are even several DNA fragments in the blood, they will be detected using PCR and an accurate diagnosis will be made.This is the main difference of this method from other methods of diagnosis - ELISA, a general blood test and others.
- Specificity.When conducting PCR, there is no such thing as a false positive or false negative result.Unlike the enzyme immunoassay( ELISA).
- The ability to analyze directly on several pathogens from a single sample of biomaterial, which makes the method convenient for the patient - you do not have to take the analysis several times.
- Fast.It is not necessary to isolate and grow the pathogen on nutrient media, as it is done in bacteriological studies.The result can be ready already on the day of the analysis.
- With the help of PCR, causative agents of latent diseases are identified when there is an agent in the body, but it has not yet caused the disease, or when the patient is the carrier of the infection( hepatitis or HIV).
- Low cost.The price of PCR analysis for one pathogen is 250-500 rubles.Slightly more expensive is a semi-quantitative analysis for viruses - about 1000 rubles.
Disadvantages of theanalysis
PCR is a high-tech method of research and makes great demands on the equipment of the laboratory.The room where the analysis is done must necessarily be equipped with a biological filter, since in the air there are always skin particles, saliva containing DNA molecules in its composition.Non-compliance with the technique of working with biomaterials can cause an incorrect result.
Analysis of blood - transcription in adults( PCR)
The interpretation of the results of this study is not difficult, because there is no table of standards for blood analysis for PCR. Only two sentences can appear in the results form:
- negative result - the causative agent for which the analysis was performed was not detected;
- positive result - the body has an agent of the disease.
It should be noted that PCR can be positive even in the absence of clinical symptoms of the disease!The interpretation of the blood test for PCR in children does not differ from that in adults.
Who needs to take an analysis for PCR
Anyone can donate blood for research.A direct indication for the study is the suspicion of sexually transmitted infections( chlamydia, gardnerellez, HIV infection).In case of unintended unprotected sexual intercourse, only PCR will help to diagnose at an early stage if a person has contracted any disease.Mandatory blood for the TORCH-complex is given by pregnant women.And also women, only planning pregnancy.
Although PCR is the most effective method of diagnosis, it's not worth it to focus on it.The examination of the patient for any disease should have a comprehensive approach.If the chain polymerase reaction allows to identify the causative agent, the serological test allows to evaluate the effectiveness of treatment, the reaction of the organism to the pathogen and drugs.All physicians should prescribe all the examinations.
You can see how the PCR blood test is performed by viewing this video review:Gudkov Roman, resuscitator