Blood Culture Collection FAQs

In U.S. hospitals, blood culture tests are frequently collected at patient admission to identify existing bloodstream infections. Hospital-acquired bloodstream infections are often considered preventable and may lead to financial penalties under value-based reimbursement programs.⁴⁵

Clinical symptoms in a patient that may indicate a possible bloodstream infection are: 

• Undetermined fever (≥ 38 degrees C) or hypothermia (≤ 36 degrees C)
• Shock, chills, rigors
• Severe local infections (i.e., meningitis, endocarditis, pneumonia, pyelonephritis, intra-abdominal suppuration)
• Abnormally raised heart rate
• Low or raised blood pressure
• Raised respiratory rate

Current clinical guidelines recommend that blood cultures should be collected:

• As soon as possible after the onset of clinical symptoms.
• Ideally, before the administration of antimicrobial therapy.
• If the patient is already on antimicrobial therapy, recovery of microorganisms may be increased by collecting the blood sample immediately before administering the next dose and by inoculating the blood into culture bottles containing specialized antimicrobial neutralization media.

Source: BioMerieux, Inc. Blood Culture: A Key investigation for Diagnosis of Bloodstream Infections.

A blood culture test is used to help determine if a patient has a bloodstream infection, also known as bacteremia or septicemia. This condition can be life-threatening. Ideally, blood culture test results guide proper antimicrobial therapy, an important aspect of antibiotic stewardship.

Blood culture testing aims to: 

• Confirm the presence of microorganisms in the bloodstream. 
• Identify the microbial etiology of the bloodstream infection.
• Help determine the source of infection (e.g., endocarditis).
• Provide an organism for antimicrobial susceptibility testing (AST) and optimization of antimicrobial therapy.

For routine bacteremia/sepsis evaluation in adults, draw two sets of blood culture bottles (aerobic and anaerobic) from two separate venipuncture sites. Per the CDC, a separate venipuncture site should be used to collect the secondblood culture set.³²

When there is persistent fever or bacteremia, additional cultures may be indicated to assess ongoing infection or to document clearance of bacteremia after initiation of antimicrobial therapy. ³⁷

When there are prosthetic valves, suspected endocarditis, or other high risk cardiac conditions, the American Heart Association⁶⁹ and IDSA³⁷ recommend obtaining at least three sets of blood cultures from separate venipunctures, ideally collected over the first 24 hours. This increases sensitivity for detecting intermittent bacteremia and helps guide optimal therapy.

There are three approaches to calculating cost: literature review, internal financial review, and adjusted patient length of stay (LOS).

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1. Numerous peer-reviewed studies have sought to assess the increased cost of care associated with contaminated blood cultures. Examples include:

• The CDC cites $4,538 – Doern GV et al.¹⁴
• $5,200 – Allain M.³⁰
• $7,200 – Sutton J et al.²⁹
• $4,580 – Rupp ME et al.⁸ 
• $4,500 - $10,078 – Garcia RA et al.³ 

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2. For facility-specific costs, a methodology is offered by Allain M: ³⁰

1. Work with the finance department to evaluate patient records.
2. Identify patients with similar DRGs and like co-morbidities.
3. Compare patients for whom the only notable difference was the presence or absence of a false positive blood culture.

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3. An approximation of costs can also be derived by assessing the LOS for each patient with a contaminated culture as well as the average cost the hospital bears for caring for each patient per day. Literature suggests the extended LOS is anywhere from 2-5 days.^7,30,51 Including LOS, the estimated cost of unnecessary treatment could add $4000-10,000 to the total cost of care.

Review average LOS by level of care and state

Unfortunately, blood culture contamination is a persistent problem in gathering reliable test results. It is reported that 20%–60% of positive cultures are false positives resulting from skin contaminants.^{46, 47, 48}

Two sets of cultures (a set = 1 aerobic & 1 anaerobic bottle) are drawn from two separate venipuncture sites (1 set from each site). This helps to distinguish true bloodstream infection (in which both specimens will be positive with the same organism) from false positive results due to contamination in which only one specimen set will be positive with non-pathogenic organism.

Clinical guidelines^{35,70, 71} recommend obtaining at least two sets of blood cultures from separate sites for the following reasons:

• Improved diagnostic accuracy – Two sets of cultures from separate sites help distinguish a true blood stream infection from contamination.
• Sampling from a single site risks misclassification, may make interpretation more difficult, go against CDC standard operating procedure for blood culture collection, and complicate surveillance classification. 
• Separate sites minimize the risk that a lapse in collection technique will produce a false-positive result or a reportable CLABSI by definition.
• Multiple site collections increase the likelihood of identifying pathogens early, supporting timely therapy and diagnostic stewardship.

In short, drawing specimens from two separate sites aligns with best practice guidelines and standard of care, ensuring accuracy of results and reporting metrics and improving quality of patient care.

Many bacteria colonize the skin as part of the body’s natural defense mechanism. Skin antisepsis can be performed before collecting the blood culture. If aseptic steps are not properly followed, skin bacteria can transfer to the bottle and cause false positive results. However, even if skin antisepsis is properly followed, microbes within the deeper skin layers can evade surface antisepsis methods and may be transferred to the specimen when the skin plug is cored out with needle venipuncture.

Research indicates that using a method, often called “sidelining”, “diverting” or “wasting,” to prevent the initial flash of blood (as little as 0.15 mL) from entering the bottle will greatly reduce BCC rates.^12,18 This can be accomplished using a blood culture collection set with integrated passive flash technology that automatically sidelines the initial aliquot of blood.

According to NHSN⁹⁰:

A laboratory-confirmed bloodstream infection (LCBI 1) is a primary infection (not related to an infection at another site) in the blood that has been verified with growth of a recognized bacterial or fungal pathogen identified from one or more blood culture specimens.

A laboratory-confirmed bloodstream infection (LCBI 2) is identified in a patient of any age with at least one of the following signs or symptoms: fever (>38.0 degrees C), chills, or hypotension AND organism(s) identified in blood is not related to an infection at another site AND the same NHSN common commensal is identified by culture from two or more blood specimens collected on separate occasions.

Source: NHSN. Bloodstream Infection Event (Central Line-Associated Bloodstream Infection and Non-central Line Associated Bloodstream Infection) January 2025.

There are two methods commonly used to sideline the initial aliquot of blood away from the blood culture specimen.

Automatic (or passive) – Fully integrated device that operates automatically during collection without requiring any user-performed mechanical or manual action to separate the flow path of blood within the device. The collection process is seamless and more compliance-friendly, leading clinicians to report a preference for passive technology over manual (user-activated) methods.^12,13 Automatic technology has been reported in literature to reduce blood culture contamination (BCC) by more than 80%. Kurin technology is automatic, offering devices that are designed to passively divert contaminants without changing caregiver workflow.

^‍Manual (or user-activated) – A device or method that requires users to physically change the direction of flow, often manually, by a step of activating a button, switch, plunger, etc. or to attach a waste tube. The devices can be a closed vein-to-bottle system or open, meaning they are exposed to touch contamination (e.g., syringe/waste tube.) Manual devices or user-activated methods can be easily bypassed, operated incorrectly, and performed out of proper sequence. When these devices are cumbersome, they can create strong aversion by end-users to utilize in their workflow, introducing difficult obstacles to sustain compliance. Examples of user-activated devices include Magnolia Medical Technologies Steripath®, VI Bypass Syringe, waste tubes, and syringes.

Passive diversion devices are designed to automatically engage as part of the normal blood draw process, with no added steps. Passive technology minimizes the workflow burden, making compliance less dependent on user attentiveness. In contrast, user-activated diversion devices and manual discard methods require deliberate activation or handling of additional components by the clinician, all of which create opportunities to misuse the device or omit using diversion altogether.

Yes. Published studies show that the benefit of diversion devices is linked to the adherence of clinicians using them as intended. Passive designs support adherence. Arnaout et al (2025) showed that in an emergency department, contamination rates declined in proportion to the weekly use of a passive, integrated diversion device. The investigators analyzed both “intention to use” and “actual-use,” and found greater compliance correlated with better outcomes. 

Conversely, evidence suggests that cumbersome workflows reduce the sustainability of improved clinical outcomes. Febres-Aldana et al (2024) reported that adoption of multi-step diversion devices was initially low (estimated at < 25%), requiring additional manual verification and tracking steps of device utilization.⁷⁶ Procedural complexities in using a diversion device can lower caregiver adoption, increase the risk of user error, drive noncompliance, and require staff time to monitor utilization. Hospitals that pilot multi-step diversion devices report difficulty sustaining use as evidenced by Buzard et al (2023) in which the authors state, “Over half of the contaminants in the ISDD [Initial Specimen Diversion Device] group were contributed to nurses not utilizing the ISDD. Although re-education was occurring, some nurses simply chose not to use the device.” ⁷⁷

Clinicians and patients are more likely to accept a blood culture diversion method when the blood wasted is minimal. Arenas et al (2021) demonstrated that diversion devices were effective irrespective of the volume diverted. The only available passive devices are designed to divert and minimize waste at ~0.15 mL compared with user-activated diversion devices that can waste 1 mL or more. Based on the scientific literature of minimal waste, CLSI (2022) and INS (2024) have updated their guidance away from large diversion volumes to specify “a small amount”.

The clinical body of evidence has evolved on diversion device volumes in recent years demonstrating that larger volumes are not necessary, and superior outcomes can be achieved with smaller volumes.

2021 – VA Temple, TX, published comparison study demonstrating the efficacy of diversion at 0.15 mL vs 1.5-2 mL.¹³ 

2022 – CLSI updated M47 Principles and Procedures for Blood Cultures³⁵ to include diversion device guidance recommending the diversion of “a small amount” citing Arenas et al 2022.¹³

2023 – Kurin received FDA 510(k) passive device indication #K220677 for reducing blood culture contamination.

2023 – CDC updated their guidance³¹ on diversion from 1.0-2.0 mL to “a small amount,” citing Doern, et al. Clin Microbiol Rev 2020.⁴⁸

Aseptically prepare the venipuncture site per hospital protocol. Maintain a “hands-off” approach after the prep procedure and do not palpate the site after antisepsis. If it is necessary to touch the aseptically prepped site, re-prep the site before proceeding.

For a peripheral blood draw, use a butterfly collection set to perform the venipuncture. Watch for a "flash" of blood to confirm proper placement in the vein.

Yes. Blood culture bottles are not considered sterile, even with the dust cap in place. Remove the caps from the bottles, disinfect bottle tops per hospital policy, and allow them to dry.³¹

Whenever possible, a peripheral venipuncture sample is preferred. Blood specimens obtained from existing intravascular lines should be avoided and discouraged, as they yield higher BCC rates. Most facilities require a provider’s order when collecting blood cultures from any pre-existing intravascular line. When necessary, a sample can be drawn from a freshly placed peripheral IV, although the potential for contamination may be increased if proper technique isn’t followed.

Yes. If additional blood is required for further laboratory tests, draw the additional tubes after the blood cultures have been obtained. Drawing additional labs prior to collecting blood cultures can result in a BCC.

No. Do not shake them. After the specimens are collected in the blood culture bottles, invert the bottles slowly several times to gently mix the sample thoroughly.

Each hospital protocol may differ slightly, but in general, you will label the bottle(s) with the appropriate patient labels, including the location of the specimen collection site, such as “right arm.” For line draws, always indicate which line and/or port. Place the label vertically on the bottle and DO NOT place label over the barcode on the blood culture bottle. Be sure to reference and adhere to your facility's policy on blood culture collection and specimen labeling.

Many facilities vary in documentation practices based on which electronic healthcare record (EHR) system they use. Please verify your facility's policy and always document when best practices cannot be followed in the event of a BCC.

A blood culture set is defined as two bottles: an aerobic bottle and an anaerobic bottle. Typically, two blood culture sets (a total of 4 bottles) should be drawn. Be sure to check the manufacturer's instructions for use. Generally, for adults, the recommended volume of blood to be obtained per culture is 20 to 30 mL. Each bottle should be inoculated with approximately 10 mL of blood. It is also generally recommended that two or three bottle sets (two bottles per set) are used per septic episode, meaning, for adults, 40 to 60 mL of blood collected from the patient for the 4 to 6 bottles, with 10 mL per bottle.⁶⁸

Always follow your facility policy for pediatrics and neonatal blood collection.

The IDSA 2024 guidelines suggest using a weight-based volume per the table below.³⁷

It is important not to underfill or overfill the bottles as this can adversely affect the results. Underfilling a bottle can yield a false negative result, while overfilling can cause instruments to falsely alert a bottle as a positive blood culture.

Blood culture bottles must be standing upright to avoid backflow of the media and ensure that an appropriate volume of blood is added. Utilize pre-labeled manufacturer tick marks on the bottle labels that indicate mL increments. Some blood culture bottles have a “fill line” to help identify your target volume. If the blood culture bottles do not have a fill line, be sure to pre-mark the bottles above the media where your fill line target will be (~10 mL). Some facilities allow the use of syringes to collect blood cultures and measure the approximate volume when patients meet specific criteria. Always check and follow your facility’s blood culture collection policy before a blood culture collection procedure.

CAP (College of American Pathologists)⁵ and PQM (Partnership for Quality Measurement)⁶ both define BCC, but they approach it differently. 

• CAP defines a BCC rate as the number of cultures positive for growth of one or more commensal organisms over the denominator of all blood cultures collected and expressed as a rate per 100 cultures (e.g., 2% contamination rate). All CAP-certified hospitals are required to report their BCC rate in this manner. 
• PQM defines contamination in line with the National Healthcare Safety Network (NHSN)/Centers for Disease Control and Prevention, which is a single culture that grows a commensal organism. If two or more cultures grow the same commensal within a short window, the test counts as a true positive.

All acute care hospitals must report CLABSIs to the National Healthcare Safety Network (NHSN)/Centers for Disease Control and Prevention. BCC poses a significant challenge to accurate reporting. If a patient has a central line, a BCC can result in the reporting of a CLABSI by definition alone. With over 1.2 million BCCs occurring in the U.S. annually, the frequency and associated cost of unnecessary CLABSI reporting is significant.⁴⁹ 

In addition to the financial impact, BCC has numerous clinical consequences. Patients who are wrongly diagnosed with a CLABSI are often treated with unnecessary antibiotics with attendant risks of secondary infection, such as C. difficile, MDROs, and other antibiotic-associated complications. Inappropriate antibiotic usage is the principal driver of antimicrobial resistance, a significant and growing global problem. It is estimated that BCC results in over $1 million in avoidable costs to an average-sized hospital each year in addition to the costs associated with CLABSI reporting.⁴⁹

In addition to blood culture contamination rates becoming a complementary metric under HOB reporting, false-positive blood cultures and HOB reporting are tightly linked because blood culture testing is the only trigger for HOB.⁵⁰ A positive blood culture is a potential HOB event if collected on or after hospital day 4. False positives due to contamination can therefore artificially inflate HOB rates, even when a patient does not have a bloodstream infection. False positive tests could have quality reporting and reimbursement implications when CMS incorporates metrics into CMS payment programs.