Blood culture (clinical analyzes)

Content

Introduction

Introduction

Blood culture is a blood test that is not usually requested by the attending physician. It is, in fact, performed in emergency situations, especially in hospitalized people if a "blood infection" caused by bacteria or fungi is suspected. instead a "viral infection is suspected, other types of tests are prescribed."

Under normal conditions, blood is a sterile liquid; Positive blood culture indicates the presence in the blood of an infectious agent, which has managed to pass from the initial point of infection, usually in other body tissues to the blood, and uses it as a transport vehicle to move to other organs of the body. When this happens we speak of invasive infection.

Examples of invasive infections are those involving the heart (endocarditis and pericarditis), infections caused by catheters inserted inside the blood vessels (endovascular catheters), infections inside the abdomen (endoabdominal), infections of the soft tissues.

People undergoing surgery or treatment to reduce the activity of the body's defense system (immunosuppressive therapy) are at increased risk of developing an invasive infection.

A particularly critical consequence of blood infection is sepsis. It occurs when the presence of bacteria or fungi in the blood is accompanied by a generalized inflammatory state of the organism that can very quickly compromise the functioning of many organs (septic shock).

Blood culture should be done as quickly as possible if an ongoing invasive infection is suspected. In the case of sepsis, a condition in which immediate intervention is particularly important, so-called antibiotics are administered while awaiting the results of the blood culture. broad range, i.e. able to act against numerous types of bacteria. Antimicrobial therapy is replaced by more targeted treatment after the identification of the organism responsible for the infection.

The test

The test

The blood sample is taken, after skin disinfection, from a peripheral vein (for example, from the arm) and then inserted into two bottles (about 8-10 milliliters of blood in each) that already contain suitable substances ( culture medium) to the growth of microorganisms. The use of two bottles, which make up a set, constitutes the common procedure for blood culture. The sampling is also performed from at least two different veins and at least one hour apart from each other, both to ensure that the microorganisms present are not due to contamination of the sample, but represent really the cause of the infection, both to increase the probability of discovering microorganisms present in the blood in small quantities or intermittently.

In infants and young children, the amount of blood drawn is less and adequate for their body weight. Furthermore, it is sufficient to carry out a single sample since often the number of bacteria present is high.

Together with blood culture, in general, the doctor requires other specific tests to evaluate the general health of the person and the complete blood count, to check for any increase in white blood cells (leukocytes), indicative of the presence of an infection.

The bottles containing the blood are then placed in incubators which guarantee the right temperatures and conditions to favor the growth of any microorganisms present.

The results

The results

The reliability of the blood culture result depends on many factors including, mainly, the speed of execution, the method of skin disinfection before taking the sample, the accuracy of the sample, the quantity of blood drawn, the speed of arrival. of the answer.

Many laboratories have introduced fully automated commercial systems, with continuous blood culture monitoring, to allow faster and better identification of microorganisms. In this way the test results can be quickly communicated to the physician who can then prescribe the targeted therapy.

If the blood culture indicates the presence of the same bacteria or yeast in two or more sets of samples it is very likely that the person being tested has a blood infection caused by those microorganisms. A positive result for only one set of two samples could be due to microorganisms present on the skin at the time of collection. In this case, the doctor must evaluate the overall health of the person, understand if the detected bacteria or fungi are compatible with the present ailments, possibly requesting additional tests.

Once the microorganism responsible for the infection has been identified, a sensitivity test to antibiotics is performed in order to identify the most effective ones to be used in the treatment.

If all blood culture sets are negative (often reported as "no growth") even after a few days, then the likelihood of an "infection caused by bacteria or fungi is low. Confirming a negative result can take several days. This is because some types of bacteria or fungi grow slowly, especially if they are present in small quantities.

Bibliography

Bibliography

Critical Patient Infections Working Group. Infections of the bloodstream. XXXVII AMCLI National Congress. Stresa, 5-8 October 2008. Revision: September 2014

Public Health England (PHE). Research with blood culture (for microorganisms other than Mycobacterium species). Standards Unit, Microbiology Services. 2014

Sara Campagna. Blood culture. InFad Dossier: information from the scientific literature for good nursing practice. 2007; 2

Editor'S Choice 2022

Expiration of drugs

Expiration of drugs

The expiration date of a drug is the date by which it can be used. It is indicated on the outer box and on the container of the medicine; usually, there are 2 digits to indicate the month and 4 digits for the year mm-yyyy (for example, 09-2018 for

!-- GDPR -->