# Blood Culture

## Overview

This module describes how to draw blood under sterile conditions and inoculate into a culture medium for microbiological investigations, when suspecting bacteraemia or sepsis.

## Indications

1. Features of

   sepsis
   sepsis

   Typical features include tachycardia, tachypnoea, pyrexia or hypothermia, altered mental state and hypotension.

2. Certain localised or systemic infections that could cause bacteraemia/fungaemia such as infective endocarditis, meningitis, septic arthritis, or systemic fungal infections

3. Intravascular

   catheter related
   catheter related

   In these cases, one culture should be taken from the IV cannula lumen, and the other from another site. Other than for this specific indication, blood cultures should never be drawn from an IV cannula.

   bloodstream infections

4. In some cases to monitor the efficacy of antimicrobial treatment

## Contraindications

1. Damaged skin, swelling, sclerosed veins, haematomas or skin infection at the drawing site
2. AV fistula or IV cannula site on the same limb

## Patient information and consent

Always verify your patient’s identity and obtain informed consent before proceeding.

### How do I explain this procedure?

“I need to draw blood from you to test for infections.”

### What can my patient expect?

“You may feel a sharp sting when I insert the needle. This blood test may take a little longer than usual blood tests and I may need to take blood from two or three places. Afterwards, the test results can take several days.”

### What is my patient’s role?

“Let me know if you have any allergies or a bleeding tendency, or use blood thinners. Fearing blood or needles is normal, but tell me if you have fainted from it. Everything must stay very clean to do this test. Keep as still as possible, and don’t cough, sneeze or reach over the equipment. Don’t touch the top of the paper I put over the area. Afterwards, press firmly on the area with cotton wool to prevent bleeding.”

## Preparation

Prepare a trolley with equipment.

### Documentation

1. Laboratory request form
2. Patient labels
3. Patient notes

### Equipment

1. Sterile gloves

2. Alcohol-based hand rub

3. Sharps container
   Sharps container

   If a sharps container is not within arm's length, use a kidney dish or other hard container to temporarily hold used sharps and to carry them to the sharps container for disposal.

4. A sterile pack (preferably a blood culture pack)

5. Skin disinfectant
   Skin disinfectant

   Commonly used preparations include 0.5-2% chlorhexidine in 70% alcohol (Steriprep), or 10% povidone iodine. There is no consensus on the superiority of one agent above another. Caution: chlorhexidine solutions may be associated with burns and skin breakdown in infants < 2 months old.

6. Tourniquet

7. Blood culture

   collection bottle
   collection bottle

   For routine cultures, an aerobic bottle alone is sufficient, as many anaerobes will also grow in aerobic culture medium. Anaerobic bloodstream infections are uncommon. Specific anaerobic bottles, fungal culture bottles and Mycobacterial bottles may be used if these infections are suspected. Inoculate aerobic bottles first to expel residual air in the needle into an aerobic environment.

8. A 22 G or larger

   needle
   needle

   One needle is used both for drawing blood and inoculating the bottle. At this point, there is not sufficient evidence to suggest using two separate needles.

9. A

   10-20 ml syringe
   10-20 ml syringe

   20 ml if you need to draw blood for other tests as well

10. An alcohol swab

11. Cotton wool and a plaster

12. Laboratory specimen bag

## Site & Positioning

See Venous Blood Sampling, or if no venous sites found, Arterial Blood Sampling.

## Procedure

Follow medical asepsis with sterile gloves.

1. Perform hand hygiene.

2. Open the sterile pack and create a sterile field on a

   clean
   clean

   Clean the table with surface disinfectant and allow it to dry.

   , dry surface. Pour skin disinfectant into the well. Open the needle and syringe onto the sterile field.

3. Flip the lid off the blood culture bottle,

   clean it
   clean it

   You may leave the swab on top of the bottle or not, but ensure that the stopper is dry before you inoculate the bottle.

   with an alcohol swab, and place it beside the sterile field.

4. Secure the tourniquet above the chosen puncture site.

5. Perform hand hygiene and don sterile gloves.

6. Clean the puncture site. Allow to dry.

7. Drape the puncture site with the

   sterile sheet
   sterile sheet

   Blood culture packs contain a fenestrated drape (with a hole in the middle), but these packs are not always available. In a pinch, you can use any sterile pack and tear a hole through the sterile sheet provided.

   from the sterile pack. You may touch the whole sheet.

8. Attach the needle to syringe and draw at least 10 ml of blood. Uphold principles of sterility.

9. Release the tourniquet with your non-dominant hand before withdrawing the needle. Your non-dominant hand is now non-sterile.

10. Use your non-sterile hand to apply gentle pressure with a dry cotton bud;

    ask
    ask

    Do not ask the patient to bend their arm, as this increases the risk of a haematoma.

    the patient to take over.

11. Inoculate
    Inoculate

    Without holding the bottle, pierce the top with the needle and allow the 10 ml blood to run into it without pushing in the plunger.

    the bottle. If you have other tubes to fill, fill them afterwards.

12. Dispose of medical waste safely.

13. Secure the cotton bud with a plaster if the site is still bleeding.

14. Rotate the bottle gently.

    Label it
    Label it

    Ensure the label does not cover the peel-off label or bar code on the bottle. Do not peel off the label and stick it in the patient's folder as it is used by the laboratory. You may stick it on the laboratory request form to aid with specimen identification.

    and transport it to the laboratory in a specimen bag with the laboratory request form.

15. Record completion of the procedure in patient notes.

## Troubleshooting

I broke sterility.

Don’t risk contamination. Dispose of everything except the blood culture bottle, and start over.

Something fell off my sterile field and I’m gloved up.

Call for an assistant to collect the equipment and open it onto your sterile field while you wait. If nobody is available, collect the equipment yourself, then put on a new pair of sterile gloves and continue.

I couldn’t get a full 10 ml of blood.

You need a full 10 ml of blood. Don’t try to take a little more from another site and put it into the same bottle. Start over completely at a new site with a new bottle.

I want to use a femoral site for blood culture.

Only as a last resort, as these sites have a higher risk for contamination than upper limb sites. Be especially meticulous about skin antisepsis when using these sites.

Also see Venous Blood Sampling and Arterial Blood Sampling.

## Risks

See Venous Blood Sampling and Arterial Blood Sampling.

1. False positives
   False positives

   Proper skin cleansing and good aseptic technique reduce the rate of false positives, where skin commensals are cultured instead of pathogenic microbes This results in misdiagnoses and inappropriate antibiotic use.

   caused by specimen contamination

2. False negatives
   False negatives

   To reduce the risk of false negatives, draw no less than 10 ml of blood. Take two to three separate blood cultures from different sites. The results of a single blood culture are often difficult to interpret.

   caused by inadequate sampling

## References

1. Fabre V, Sharara SL, Salinas AB, Carroll KC, Desai S, & Cosgrove SE. Does This Patient Need Blood Cultures? A Scoping Review of Indications for Blood Cultures in Adult Nonneutropenic Inpatients. Clinical infectious diseases: an official publication of the Infectious Diseases Society of America. 2020;71(5):1339–1347.
2. WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy. Geneva: World Health Organization; 2010. Available from: https://www.ncbi.nlm.nih.gov/books/NBK138665/.
3. Ntusi N, Aubin L, Oliver S, Whitelaw A, Mendelson M. Guideline for the optimal use of blood cultures. S Afr Med J. 2010;100(12):839-843. Published 2010 Dec 1. doi:10.7196/samj.4217