Blood Culture Health Article

Definition

A blood culture is a lab test designed to detect the presence of bacteria, yeast, or fungi in the bloodstream. A routine blood culture involves injecting a sample of the patient's blood into two bottles of sterile nutrient broth (one for aerobes and one for anaerobes), incubating the bottles at 35°C, and monitoring the bottles for growth over a period of five days. For positive cultures, it also involves identifying any organism that grows and performing antibiotic sensitivity tests to determine which antibiotics will be effective in treating the infection.

Purpose

Physicians normally order this test for patients with symptoms of bacteremia. Symptoms can include fever, chills, mental confusion, anxiety, rapid heartbeat, hyperventilation, blood clotting problems, and shock. These symptoms are especially significant if the patient already has another illness or infection, is hospitalized, or has trouble fighting infections because of a weak immune system. Because bacteremia can be a serious clinical condition that, untreated, can lead to death, a blood culture should be performed as soon as an infection is suspected. Early detection will give the patient the best chance for effective treatment and survival.

Blood cultures are sometimes used to determine the causes of infections in other parts of the body because these infections often spread to the blood. For example, bacterial pneumonia (an infection of the lung) and infectious endocarditis (an infection of the inner layer of the heart, including the heart valves) are known to leak bacteria into the bloodstream. Other sources might be boils, urinary tract infections, and oral bacteria spread during mouth trauma (such as injury or dental treatment).

Precautions

Patients who have bleeding disorders or are taking blood thinners might have trouble with bleeding following a venipuncture. Before having a blood sample drawn, such patients should tell the phlebotomist about their condition.

Description

There are many variables involved in performing a blood culture. Before ordering a blood culture, the physician must make the following decisions based on a knowledge of infections and the patient's clinical condition and medical history.

• type of blood culture that will best target the suspected microorganism
• number of blood cultures to request
• how often the blood cultures should be performed

Some factors influencing these decisions are the patient's symptoms or previous culture results, and whether or not the patient has had recent antibiotic therapy.