Taking blood from a patient poses a consent issue for a medical student on placement. Dr Carol Chu discusses the scenario.

The scenario

A medical student was asked by the surgical FY2 to take blood from a patient who had just had a procedure done under general anaesthetic.

The student approached the patient and introduced himself. He told her he was there to take a blood sample. The patient was very sleepy, but moved her left arm slightly as if presenting it for blood sampling. The student noticed that she had an intravenous line in that arm and so proceeded to take the sample from the right arm.

The next day he was told by the FY2 that the patient had complained. She had previously had breast cancer and surgery on the right side, and she had lymphoedema in that arm. She had specifically stated that she did not want any blood sampling or cannulae in that arm, and said the student had not only taken blood without her consent – but also against her specific wishes.

MDU advice – what makes consent valid?

In order for consent to be valid, it must be:

  1. Voluntary – the person who is being asked for consent must make the decision themselves, with no undue pressure from anyone else.

  2. Informed – the person being asked for consent must know what the treatment or investigation entails, including the risks, benefits and alternatives, and the person consenting must have the capacity to make the decision.

An adult patient is assumed to have capacity unless it is proven otherwise. A patient with capacity should be able to understand the decision to be made, to recall it long enough to weigh up the decision to be made, and communicate the decision by talking, using sign language or by any other means.

A patient with capacity can consent or refuse any treatment or investigation for any reason, or no reason at all.

Loss of capacity

Patients may have permanent or temporary loss of capacity. Temporary loss of capacity can occur as the result of unconsciousness, or if the patient is under the influence of medication.

Consent may be implied or explicit. Explicit consent can be given verbally or in writing. The GMC's guidance on consent says that for minor or routine investigations or treatments, it is usually enough to have oral or implied consent if you are sure the patient understands what you propose to do and why. 

The GMC updated its guidance on consent in November 2020. The updated guidance, Decision making and consent, places greater emphasis on doctors and patients taking decisions together based on exchange of relevant information specific to the individual patient.

Patients may give implied consent for minor procedures or examinations by complying with the proposed procedure, for example by rolling up their sleeve and putting out their arm to have blood pressure taken.

In cases which involve higher risk, consent should normally be written. By law, you have to get written consent for some treatments, such as fertility treatment.

Photo credit: Bigstock


In the above case, it is likely that the patient had a temporary lack of capacity due to the anaesthetic drugs, and should not have been asked to make a decision at that time. In an emergency, treatment may be given to a patient who lacks capacity in their best interests – but if it is thought that the loss of capacity may be temporary, then the least restrictive option should be chosen until the patient is able to make their own decision.

Putting out an arm for a blood sample could be taken as implied consent. However, the patient put out her left arm rather than the right arm, which could indicate that she wanted that arm used. The student used the other arm.

In this situation, the student should have asked the FY2 how urgent the blood sample was. Could it wait until the patient was able to consent?


The medical student met with the consultant and after discussion with him, apologised to the patient for taking the blood out of the arm that she had not wanted used for this purpose. The patient accepted his apology, as there was no harm done.

On reflection and discussion with the consultant, the student said that in future he would always ask for some background on a patient before carrying out any procedure. He also agreed that it was important to check whether the procedure was necessary at that time.

This page was correct at publication on 08/06/2017. Any guidance is intended as general guidance for members only. If you are a member and need specific advice relating to your own circumstances, please contact one of our advisers.