This guideline covers obtaining blood samples from intermediate to long-term central venous access devices at Great Ormond Street Hospital (GOSH).
Note: While this guideline refers to the 'child' throughout, all activities are, of course applicable to young people.
- Skin tunnelled, cuffed central venous catheters (CVCs) (commonly referred to as Hickman® catheters, Broviac® catheters). These CVCs may have one, two or three separate lumens.
- Implanted ports (IP) (commonly referred to as ports, port-a-cath®, Bardport®). May have one or two reservoirs. Each reservoir is attached to a separate catheter.
- Peripherally inserted central catheter (PICC) (commonly incorrectly referred to as long-line, PIC, short long-line). There are two types of PICC used within GOSH: open ended, ie Cook® peripherally inserted central catheter with clamps in situ or valved catheters ie Groshong® NXT ClearVueTM PICC). These catheters may have one or two separate lumens.
For more information about these types of CVAD refer to Great Ormond Street Hospital (GOSH) clinical procedure guideline on central venous access devices - long term
General guidance when obtaining blood samples from CVADs
When obtaining blood samples from CVADs, care should be taken to ensure that blood loss is minimal, the potential for infection is minimised and an accurate sample is obtained (Registered Nurses Association of Ontario (RNAO) 2005; Bravery 2008
Minimising blood loss
Frequent blood sampling can lead to a risk of nosocomial blood loss (Frey 2003; RNAO 2005; Cole et al 2006; Adlard 2008
). Neonatal and paediatric patients are particularly at risk of volume depletion (Frey 2003
). For neonatal/paediatric patients the amount of blood taken for blood samples should be documented (Frey 2003; Royal College of Nursing (RCN) 2010; Infusion Nurses Society (INS) 2006
). Only the volume of blood needed for accurate testing should be obtained (INS 2006
The child’s general state of health must be considered prior to any blood sampling especially where multiple blood samples are required. In children where their illness or treatment can deplete blood volume, haemoglobin or hinder their replenishment, extra caution must be used (Howie 2011
The volume of blood obtained for each test should where appropriate be the minimal volume required for each test. The volume of required blood is commonly listed on the blood forms. Any queries in relation to the volume required can be directed to the laboratory or the team requesting the test.
Blood sampling should be coordinated and the number of entries to the CVAD minimised to conserve blood loss (RNAO 2005
Reducing the potential for infection
Use of an aseptic non touch technique (ANTT) and good standards of hand washing can reduce the risk of infection when using CVADs. ANTT must be used when accessing CVADs, hands must be decontaminated and an effective hand washing technique used. Clean or sterile gloves should be used when accessing CVAD's (Pratt et al 2007). Refer to Aseptic Non Touch Technique (ANTT) for intravenous therapy and hand hygiene clinical guidelines.
The GOSH CVL care bundle (PDF), adapted from the Department of Health's 'Clean Safe Care - Reducing Healthcare Acquired Infections' High Impact Intervention - Central Venous Catheter Care (DH, 2010), should be adhered to when accessing CVADs. This care bundle program aims to reduce catheter related blood stream infections.
Standard principles for preventing health-care associated infections should be applied when obtaining blood samples from CVADs ie hand hygiene, use of personal protective equipment (PPE) and the safe use and disposal of sharps (Pratt et al 2007).
Personal protective equipment (PPE) should be selected and used based on assessment of the risk of transmission of microorganisms to the patient and carer, and the risk of the healthcare practitioners' clothing being contaminated by patients' blood, body fluids, secretions or excretions.
Infection risks to staff - gloves should be worn for activities that carry a risk of exposure to blood (Pratt et al 2007). Disposable plastic aprons should be worn when there is a risk that clothing may become contaminated with blood (Pratt et al 2007).
Sharps, ie any needles used for blood sampling, should be used safely and disposed of correctly (RCN 2010; Pratt et al 2007). Refer to sharps disposal guideline and exposure to blood borne viruses.
Obtaining an accurate sample
Coagulation and drug levels obtained from CVADs may be inaccurate (RCN 2010; Bishop et al 2007
Published literature, national and international guidelines do not support the practice of obtaining blood samples for coagulation studies from heparinised CVADs (Mayo et al 1996; Frey 2003; Hinds et al 2002; Oncology Nurses Society 2004; RNAO 2005; RCN 2010
). Hinds et al (2002)
found that even a 12ml discard volume was not sufficient to yield a clinically trustworthy Prothrombin time (PT) or Activated Partial Thromboplastin Time (APTT) value in children and adolescent cancer patients with tunnelled CVADs. If the results of coagulation tests are used to monitor anticoagulation treatment or evaluate coagulopathy, heparinised CVADs should not be used (Frey 2003
). If there is any doubt as to the accuracy of coagulation studies the sample should be obtained from a peripheral vein (Bishop et al 2007
For haematology/oncology patients: when the patient is due a procedure under anaesthesia (eg intrathecal methotrexate and lumbar puncture) and coagulation studies are required pre procedure to determine whether cryoprecipitate or fresh frozen plasma is needed, peripheral samples should be taken to avoid delays to the theatre lists and possible cancellation of the child's procedure. These patients may have low fibrinogen levels following administration of asparaginase or exhibit abnormal clotting during induction/consolidation therapy as a side effect of their chemotherapy.
Drug levels obtained from CVAD's may be inaccurate (McBeth et al 2004; Oncology Nurses Society 2004; RNAO 2005; Boodhan et al 2006
). The literature does not support the use of silicone catheters for sampling drug levels if the drug is being administered via the same catheter (Frey 2003
). However blood samples may be safely obtained from a ciclosporin-naive lumen (ie the lumen not used to administer the drug) of a dual/triple lumen catheter (Senner et al 2005; Bishop et al 2007
Blood samples for antibiotic assay must not be taken through the same catheter that has been used to administer the antibiotic (GOSH 2011
The heparinised saline or saline present in the device should be removed prior to obtaining a blood sample to avoid erroneous results (Bishop et al 2007
If the patient has an infusion in progress, this should be stopped before obtaining blood samples (Frey 2003; RCN 2010; INS 2006
Blood samples must be drawn and put into blood bottles in the correct order (GOSH 2007
Methods of obtaining blood samples from CVADs
Several different methods are described to obtain blood samples via CVADs. There is no current consensus as to which is the most appropriate/effective/safe method. The literature provides little direction for determining the optimal method of blood sampling from CVADs (Adlard 2008
). There are potential complications associated with each method (see table 1 below) (RNAO 2005
The three main methods are:
The discard method is the most commonly used technique (Keller 1994; Adlard 2008
). The reinfusion method is not widely used in practice (Adlard 2008
). A recent study by Aldard (2008
) supports the use of the push-pull technique for blood sampling from CVADs.
The discard method is the most commonly used technique within GOSH.
Table 1 A comparison of the different methods of blood sampling
|Method ||Description ||Advantages ||Potential |
|Remove a specified amount of blood from CVAD via a syringe or vacutainer. Use a new syringe for the sample. Flush the CVAD with sodium chloride 0.9%. |
|Removes potential contaminate from the CVAD. |
No blood is returned to the child that might introduce pathogens.
|Potential nosocomial blood loss with frequent blood samples. |
Potential to confuse a discard syringe with blood sample syringe.
|Push - Pull |
|Use a 10 ml syringe. Flush the CVAD with sodium chloride 0.9%. Without removing the syringe, aspirate 6ml of blood, then push it back into the CVAD. Repeat this process x 3. Remove the empty syringe and attach a new syringe to obtain blood sample. Flush CVAD with sodium chloride 0.9%. |
|Requires mixing the blood back and forth in a syringe several times to eliminate contaminates from the CVAD. |
Limits blood loss as no blood is discarded and potential exposure to pathogens.
|May be difficult to obtain enough blood for three to four push-pull sequences particularly with malfunctioning catheters. |
Risk of haemolysis with the agitation of blood.
Table comparing different methods of blood sampling
|Involves returning the discard specimen after obtaining the samples. |
Minimises blood loss.
|Aspirate 6ml of blood into a syringe and attach a sterile cap. Obtain blood sample via a syringe or vacutainer. Re-infuse the discard from the first syringe. |
|Potential to re-infuse clots. |
Potential for contamination of the blood being reinfused.
Potential for error including the possibility of confusing the discard syringe with the blood sample.
(Frey 2003; RNAO 2005; Adlard 2008
There is no consensus and limited research as to amount of blood to withdraw/discard or the amount of flush to use after obtaining a blood sample from a CVAD.
The required amount of blood to be discarded before obtaining a sample is likely to be a function of the intra-luminal volume of the CVAD. This volume varies according to the type and size of the CVAD and ranges from 0.15-2.3mls. Standard practice in the UK is to withdraw a discard volume of 5mls. This amount greatly exceeds the estimated intraluminal-volume and is applied to all types and size of CVAD (Cole et al 2006
Some authors recommend a discard of three times the catheter volume to clear the CVAD of infusate (Frey 2003
). A study by Cole et al (2006
) found that a 3ml discard volume was sufficient to ensure the subsequent blood sample was not diluted or contaminated by residual fluid within the CVAD. This recommendation applies to blood samples obtained for clinical research studies and routine clinical analysis. It did not include coagulation studies.
For PICCs some adult guidelines recommend a discard volume of 1-2mls (Oncology Nurses Society 2004; Hagle 2007
), the manufacturers of Groshong® NXT ClearVueTM PICC
suggest a volume of 5mls (Bard Access Systems Inc. 2003
). One paediatric reference recommends 2mls (Frey 2007
). As the intraluminal volume of a PICC is less than a skin tunnelled CVC or implanted port it is postulated that a discard volume of 2mls would be sufficient.
| CVAD type |
| Discard volume |
|Skin tunnelled central venous catheter |
|Implanted port |
Table showing discard volumes for withdrawing blood directly from the catheter hub or needle-free connector.
|Peripherally inserted central catheter |
The discard volumes above are for withdrawing blood directly from the catheter hub or needle-free connector. If the sample is withdrawn through add-on devices eg stopcocks, ramping systems, extension sets the dead space of the add-on should be added to the discard volume.
CVADs should be flushed with sufficient sodium chloride 0.9% to clear the CVAD of all residual blood after blood sampling (RCN 2010; RNAO 2005; INS 2006
Small syringes exert less negative pressure when withdrawing blood samples from CVADs (Macklin 1999; RNAO 2005
). If difficulty is experienced withdrawing blood from a CVAD, switching to a 5ml syringe or smaller may help (Macklin 1999
Blood sampling from PICCs smaller than 4 Fr is not recommended by some authors and manufacturers of these devices due to a risk of catheter occlusion from blood remaining in the catheter (Knue et al 2005
). However a study by Knue et al (2005
) showed that blood sampling was feasible and effective through 3 Fr PICCs in children. This practice was not associated with a significant increase in occlusion, infection or mechanical complication rates. Within Infection, Cancer and Immunity at GOSH we have not found blood sampling from PICCs less than 4 Fr to be problematic.
The largest lumen of a multi lumen CVAD should be used for blood withdrawal (Frey 2003; RNAO 2005
The patient and the blood sample should be positively identified at the time a blood sample is obtained (RCN 2005b; INS 2006; National Patient Safety Agency (NPSA) 2007; GOSH 2008
Samples should be labelled before leaving the patient (RCN 2005b; INS 2006; GOSH 2007
Blood bottles should not
be pre-labelled (RCN 2005b; GOSH 2007
Blood sampling procedure
The following procedure must only be undertaken and followed by IV competent staff.
Inform the child and family why the blood samples are required, what the procedure will entail and how long the procedure will take (Rationale 1
Use distraction and play if required (Rationale 2
Confirm patient identity before taking blood samples adhering to GOSH patient identification policy 2012 (Rationale 3
Use an aseptic non-touch technique. Refer to Aseptic Non Touch Technique (ANTT) for intravenous therapy (Rationale 4
Wash hands using appropriate cleansing solution and dry thoroughly. Refer to hand hygiene clinical guideline
Use personal protective equipment (gloves and plastic apron).
Dispose of sharps safely and correctly. Refer to sharps disposal guideline
and exposure to blood borne viruses
- blood bottles and blood forms
- adaptors for using Monovette® system
- 3-4x10ml syringes (one for discard, one for sample, one for sodium chloride 0.9% and one for heparin if required)
- 0.9% sodium chloride
- heparin to flush the CVAD
- 21g green needle
- 23g blue needle (to withdraw heparin if required). A small gauge needle will reduce the risk of aspirating glass particles from glass ampoules (RCN 2010).
- 2% chlorhexidine in 70% isopropyl alcohol wipe
- clean plastic tray
- non-sterile gloves
- plastic apron
Prepare all equipment using ANTT (Rationale 7
Clean the catheter hub/needle-free connector with a 2% chlorhexidine in 70% isopropyl alcohol wipe for 30 seconds using friction and allow to dry (Rationale 8
Connect empty 10ml syringe.
Withdraw discard volume (see table 2
) (Rationale 9
). This can be used for blood cultures if required.
Connect empty syringe or Monovette® adaptors/blood sampling bottle.
Withdraw amount of blood required for blood samples.
When using the Monovette®
system remember the correct order of draw to prevent contamination.
Connect the syringe containing the 0.9% Sodium chloride and flush the CVAD using a push-pause/pulsatile technique to clear the CVAD of blood.
Flush CVAD with heparin (if required). Use the appropriate flushing technique recommended in the Central venous access devices - long term guideline (Rationale 10
Fill blood bottles in correct order if syringe used to obtain samples (Rationale 11
Label blood samples.
Dispose of all equipment safely.
Rationale 1: To obtain consent and compliance.
Rationale 2: To minimise anxiety.
Rationale 3: To ensure that blood sample is obtained from the correct patient.
Rationale 4: To minimise the risk of infection.
Rationale 5: To minimise the risk of infection.
Rationale 6: To reduce the risk of needle stick injury.
Rationale 7: To minimise the risk of infection.
Rationale 8: To ensure effectiveness of cleaning agent.
Rationale 9: To remove fluid in the line that may dilute the sample.
Rationale 10: To prevent reflux of blood into the catheter.
Rationale 11: To avoid contamination of the samples.
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Document control information Lead author(s)
Karen Bravery, Nurse Practitioner and IV Practice Development Lead for Infection, Cancer and Immunity
Anne Ho, Specialist Nurse - Intravenous Therapy Team, Infection, Cancer and Immunity
Katherine Berry, Specialist Nurse - Intravenous Therapy Team, Infection, Cancer and Immunity
Nicola Farrell, Practice Educator - Chemotherapy/Intravenous Therapy, Infection, Cancer and Immunity
Document owner Approved by
Karen Bravery, Nurse Practitioner and IV Practice Development Lead for Infection, Cancer and Immunity
Clinical Practice Committee First introduced:
1 March 2012
3 March 2014