Why blood samples are rejected and how to reduce the risk of error

Diagnosis and treatment can be delayed if the lab says a sample is unsuitable to process

Nurses frequently practise phlebotomy, but its still a clinical skill that needs to be kept up to date

  • Repeat sampling puts patients at risk of distress and delayed diagnosis and its costly to services too
  • Straightforward tips for keeping your phlebotomy practice safe and robust
  • Read what to do if you or your patient are nervous about the procedure
Picture: iStock

Phlebotomy the drawing of blood has been practised for centuries and remains one of the most invasive procedures in health care, according to World Health Organization (WHO) guidelines .

Today, analysing blood samples is a sophisticated and expensive business. It becomes even more costly when policy and procedures


Nurses frequently practise phlebotomy, but it’s still a clinical skill that needs to be kept up to date

  • Repeat sampling puts patients at risk of distress and delayed diagnosis – and it’s costly to services too
  • Straightforward tips for keeping your phlebotomy practice safe and robust
  • Read what to do if you or your patient are nervous about the procedure
Picture: iStock

Phlebotomy – the drawing of blood – has been practised for centuries and remains ‘one of the most invasive procedures in health care’, according to World Health Organization (WHO) guidelines.

Today, analysing blood samples is a sophisticated and expensive business. It becomes even more costly when policy and procedures are not followed. A 2017 study found sample rejections cost one NHS trust almost £27,000 every month.

Sample rejection can be distressing for patients and frustrating for staff


The cost per month of blood sample rejections at an unnamed NHS trust, a 2017 study found

There are plenty of reasons why a laboratory might not process a sample. These include mislabelling or absence of labelling, using the wrong bottle, and insufficient volume of blood.

The same 2017 study, which looked at 229 haemoglobin samples, found 61 (12.2%) were rejected because they were not labelled, while 18 (7.9%) were in an incorrect bottle. In more than a third of cases (83), the reason for rejection was that an empty packet had been sent to the lab.

The financial costs associated with rejected samples arise mostly from extended hospital stays resulting from delays in diagnosis, which in turn take a toll on patients, are frustrating for clinical staff and create extra work for pathology teams.

Why do nurses take blood?

Kingston University school of nursing senior lecturer/practitioner Francina Hyatt, who has taught clinicians phlebotomy for 20 years, says the main reasons nursing staff take blood are for therapeutic monitoring – assessing an existing disease – and for diagnostic purposes.

Nursing lecturer and nurse practitioner
Francina Hyatt

In different healthcare settings, nurses will request different tests.

‘In general practice, we’ll often order quite a few different blood tests not necessarily expecting them all to come back irregular but more to eliminate thyroid problems, for example, or anaemia,’ says Ms Hyatt, who maintains her own skills as a nurse practitioner in general practice one day a week.

In acute care, blood is taken for reasons of health assessment and clinical management but there is often added urgency, such as a need to check for sepsis. In emergency departments in particular, haematology and biochemistry sampling speed up diagnosis and therefore treatment.

Why it’s important to understand laboratory procedures


of blood samples in the 2017 study were rejected because they were not labelled

So what can nursing staff do to ensure that when they take blood and send it off for analysis, the lab doesn’t send it straight back because the sample cannot be tested?

Understanding the processes involved in taking and analysing blood may reduce the risk of sample rejection. The WHO says the knowledge of staff involved in blood collection is a factor influencing the outcomes of lab results.

Policy developed by the Institute of Biomedical Science (IBMS) says clinicians who take blood samples must be familiar with and understand the rationale for laboratory standards and procedures: ‘There should be clear written guidelines for those who obtain blood samples from a patient on behalf of the requesting practitioner.’

Common reasons why samples are rejected

‘Each step in the process of phlebotomy affects the quality of the specimen and is thus important for preventing laboratory error,’ says the WHO. Its guidelines add that mistakes in completing forms and identifying patients remain common.

Rigorous adherence to labelling protocols
is essential Picture: Jim Varney

Ms Hyatt agrees incorrect labelling is often the reason samples cannot be accepted for analysis.

‘In general practice, not all surgeries will have pre-printed labels. Or the sticker won’t always make it to the right bottle. So either the lab can’t read the label or it’s the wrong label for the form. Or the wrong name has been written for the form supplied.’

The IBMS policy says standard operating procedure must instruct lab staff not to amend details on a sample.

However, the senior biomedical scientist can, in line with local protocols, exercise discretion and decide to process a sample with an inadequately labelled request form if the patient is ‘not easily accessible for a repeat’.

‘Patients are at risk of actual harm if there is a delay in diagnosing and that can have major consequences’

Francina Hyatt, nurse practitioner and Kingston University senior lecturer and practitioner

In acute care, some clinical areas appear more prone than others to blood sample rejection. A 2015 study that looked at rejected samples over a 12-month period at a hospital in Turkey found the ratio of rejected blood and urine samples was higher in emergency departments than intensive care or other inpatient services.

Poor mixing of the blood once it is in the bottle can also cause a lab to ask for a repeat sample.


of samples were rejected because an empty packet had been sent to the laboratory, the study found

‘For instance, a gold-top bottle would require five to six inversions whereas a blue-top would be three to four,’ says Ms Hyatt. ‘And it’s really quite important that the inversions are done correctly because the different additives in the different tubes preserve the sample ready to go to the lab for centrifuging.’

The additives are agents that either prevent or promote clotting in readiness for centrifuge.

How to minimise risk of blood sample rejection by the lab

It’s good to refresh your knowledge of the things you can do to reduce risk of sample rejection
Picture: John Rose

Sticking to protocol and maintaining education appear to be key to minimising the likelihood of sample rejection.

Careful tourniquet placement, stringent labelling, correct mixing, storage and transportation and correct needle size can all help ensure the sample is processed by the lab.

Researchers in the United States found that an education programme for healthcare practitioners who take blood led to an immediate reduction in sample rejection rates. But the improvement was not sustained and they recommended repeating education annually ‘or even more frequently’.

The WHO offers step-by-step practical guidance on best practice in phlebotomy. Sections include taking samples, filling the tubes, the correct sequence for sampling and preparing samples for transportation. Like the US researchers, the WHO recommends regular in-service training and supportive supervision.

Key points to remember include:

  • Invert collection tube with care The manufacturer of BD Vacutainer blood collection tubes offers guidance on correct mixing technique. It includes the exact angle – 180 degrees – to which the tube should be inverted gently
  • Draw multiple samples in correct order If several samples are required, they should be drawn in the correct order and according to the recommendations of local laboratories, the WHO says. Drawing in the wrong sequence can lead to cross-contamination
  • Minimise delays where you can Labs should receive blood samples within 24 hours of the sample being drawn. A delay does not necessarily mean the sample has to be repeated but analysis could show raised potassium, for example. In such cases, the lab will note the time lag, might suspect a false reading and therefore ask for a second sample, Kingston University senior lecturer and practitioner Francine Hyatt says
  • Be aware of the causes of unreliable readings Haemolysis – the rupturing of red blood cells – can cause elevation in potassium reading. A 2017 study said haemolysis is a common problem in blood sampling. Causes include prolonged tourniquet application, inappropriate choice of needle size, underfilling or excessive shaking of the tube. Training can play a pivotal part in overcoming these issues, the study authors said. There is also evidence that a patient’s fist-clenching during the draw can result in elevated potassium levels as a result of contraction of muscles in the forearm.

The impact for patients when samples are rejected

A rejected blood sample can mean a risk of deterioration in the patient, Ms Hyatt says. Ketoacidosis and acute kidney failure are among the conditions that can cause a threat to life if treatment is not initiated quickly. Referral can be delayed or the patient may be referred to the wrong specialty.

‘So it’s not just about frustration,’ Ms Hyatt says. ‘Patients are at risk of actual harm if there is a delay in diagnosing and that can have major consequences.’

Colour-coded tubes Picture: iStock

Ms Hyatt points out that repeating a sample is not necessarily straightforward either. At present in general practice, for example, appointments may be limited as a result of the pandemic.

The need for a second sample adds to the strain on practices, and patients trying to limit contact with health services may be especially reluctant to return or to attend their local hospital phlebotomy service.

If a patient is needle-phobic (see box below), having to draw another sample can add to the distress and anxiety experienced.

As well as outlining good practice, the WHO guidance emphasises the importance of ensuring the safety of patients and staff when blood is being taken. For clinical staff, sharps injuries and exposure to blood are obvious risks. Adherence to policies and guidelines, and using needle-safe equipment, will help reduce those risks.

Needle phobia: taking blood from a frightened patient

Picture: iStock

The charity Anxiety UK suggests that up to 10% of the UK population may have a phobia about injections and needles.

Needle phobia affects the ability of the clinician to draw the sample – and it can result in a delay to diagnosis and treatment.

If the nurse is also nervous it can exacerbate the situation so senior lecturer and practitioner Francina Hyatt says a clinician who lacks experience in drawing blood should consider asking a more experienced colleague to help – or, if no one is available, asking whether the patient would be prepared to rebook.

‘It’s really important the patient has that choice,’ she says. An anxious or inexperienced practitioner may, by missing the vein, simply worsen the patient’s anxiety.’

Distraction techniques may be necessary, especially for children Picture: iStock

Techniques to use with nervous patients

‘There are options,’ says Ms Hyatt. ‘You can use a safety blood-collection needle set, which gives you more chance you’ll get the draw. You’re more likely to be able to manoeuvre it a little and get flashback, verifying you are in the vein, rather than putting the bottle on and hoping you’re in the vein’

Ms Hyatt’s other tips include:

  • Make sure the patient is well hydrated and the arm has been hanging down
  • Ask the patient whether a particular vein is usually best. For example, they might say ‘The nurse can only ever take blood from the back of my hand’
  • Take your time to select the best vein to avoid repeated attempts
  • Use distraction techniques if appropriate and especially with children
  • Display a calm and confident approach
  • Recognise your limitations and either ask for help or consider another appointment for the patient

Daniel Allen is a health journalist

Further information

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