When a patient shows signs of a bloodstream infection, a physician will likely order a blood culture test. A blood sample is collected in two special bottles, one that fosters the growth of aerobic microbes and the other anaerobic microbes. Any microorganisms present in the sample will grow and return a positive test result, which may inform a diagnosis and trigger antibiotic therapy. However, the clinical value of blood culture testing may be compromised by improper collection technique. For example, if not enough blood is collected, a false negative may occur, allowing the infection to go undiagnosed and antibiotics to be held or discontinued, putting the patient at higher risk of sepsis. Likewise, a positive blood culture result may not indicate a bloodstream infection at all, but rather a false positive due to specimen contamination. Contaminants can come from patient skin, clinician hands, blood culture bottle tops, attachment or detachment of transfer components, and existing intravenous line. In fact, approximately 30% of the patients who test positive do not have a bloodstream infection. Hospitals strive to stay below a 3% false positive blood culture rate, but this goal still allows for far too many events, forcing physicians into a guessing game to decide if the organism discovered is a true threat. Guessing wrong can have terrible consequences. A patient may experience unnecessary stress, longer hospital stays, exposure to unneeded antibiotics, and adverse events. Hospitals absorb the cost of additional staff time, testing, treatment, and extended stays. Just one contaminated culture can add 3 to 4 days and up to $10,000 in costs, but if the patient develops a hospital-acquired condition during the extended stay, that cost could be much higher. Fortunately, the accuracy of blood culture testing can be improved by following collection best practice. Best practice blood culture collection requires the following per each set. Gloves, skin antiseptic, tourniquet, fully assembled closed system butterfly collection set, two culture bottles, one aerobic and one anaerobic. Two sets of cultures should be taken from two different venipuncture sites. Although it may seem unkind to stick the patient twice, it is important. Positive culture results from both sides will likely indicate a true bloodstream infection. But if only one culture grows an organism, the physician may suspect a contaminant. To begin, skin and bottle preparation reduces the potential points of contamination. First, disinfect the tops of culture bottles per hospital policy. Next, apply a tourniquet and locate the patient's vein. Proper skin antisepsis is critical because the most common contaminants are microbes from the patient's own skin. Wash hands and wear clean gloves. Prep the venipuncture site according to hospital policy. Do not repalpate the vein once prepped. Then, perform the venipuncture using a closed system butterfly collection set with a bottle holder. Some patients have veins that are difficult to access and could collapse under the vacuum pressure of a vacutainer culture bottle. Clinicians avoid this by using a syringe to control the pressure. However, this requires the clinician to open the system to transfer the sample to the bottle, adding steps, and significantly increasing the risk of contamination. Another open system technique is obtaining a sample from a freshly placed IV, a practice that also carries higher risk of contamination. No matter which method is used, fill the aerobic bottle first, then the anaerobic bottle, making sure to fill the bottles to the optimum volumes required per hospital policy to help ensure accurate results. Collect any additional lab vials after completing the blood culture set. After collection, withdraw the butterfly, activating the needle safety mechanism. Following hospital policy, dress the venipuncture site, and then label, document, and send the specimens to the lab. Now that we have covered the best practice basics, here's a little test. True or false? With best practice compliance, contaminated blood cultures will disappear. False. Unfortunately, skin antisepsis does not eliminate contamination from skin microbes. As many as 20% of skin microbes are unaffected by antisepsis. During venipuncture, the needle traps a minute core of dermis, and if microbes are present, they are given a straight line into the culture bottle. A butterfly set with an automated closed system specimen diversion device sends the initial flow of blood, and any contaminants therein, into a U-shaped side channel. When the collection bottle is attached, the specimen flows from the vein to the bottle in a closed system, bypassing the diverted contaminants. When necessary, a diversion device can be connected to a syringe, or used to draw blood from a fresh IV. Clinical studies have shown that the use of automated specimen diversion can reduce contaminated blood cultures by more than 80%. Blood culture collection best practice compliance, combined with closed system automated specimen diversion technology, can dramatically improve the clinical value of blood culture testing, leading to more effective and lower cost treatment of patients.

blood culture testing

diagnostic tool

bloodstream infections

collection techniques

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