Weight - Bone marrow and peripheral blood stem cell

Essential information

Definition/s

BMI: body mass index

Obligatory
  1. Bone marrow donor:
    Must not donate if:
    1. BMI is over 35.
    2. Under 50 kg (7 stone 12 lb) and the donor's weight is significantly less than the recipient's weight (see Additional information below).

  2. PBSC donor:
    Must not donate if:
    1. BMI is over 40.
    2. BMI is below 18.5.
    3. Under 30 kg (4 stone 10 lb).
    4. Under 50 kg (7 stone 12 lb) and the donor's weight is significantly less than the recipient's weight (see Additional information below).
    5. The donor is so overweight that they have difficulty in getting on to or off the donation couch.
    6. Venous access is very difficult.
Discretionary
  1. Bone marrow donor:
    1. If BMI is >35 to <40, refer to Designated Clinical Support Officer. Obtain anaesthetic opinion, considering other anaesthetic risk factors and technical feasibility.

  2. PBSC donor:
    1. If BMI is 40 to <43, refer to Designated Clinical Support Officer, considering venous access.
    2. Treatment with anti-obesity drugs, accept.

Supporting information

Additional information

UK Blood and Tissue Service staff should not put their own health at risk by helping donors on and off the donation couch except in an emergency.

It is recommended that no donor should lose more than 15% of their blood volume during any donation procedure. This is to protect them from adverse effects such as fainting. When bone marrow is donated, however, the donor receives intravenous fluid perioperatively and this allows a volume of bone marrow to be taken that is more than 15% of the donor’s blood volume. The maximum volume to be taken is determined by the donor’s weight in kilograms, and for most Transplant Centres this is up to 20 mL of bone marrow per kilogram of body weight, as per European Society for Blood and Marrow Transplantation (EBMT) guidance. Bone marrow donors also receive iron supplements post-donation to facilitate rapid recovery of any donation-related anaemia.

To ensure engraftment in the recipient, it is vital that a bone marrow harvest contains a sufficient blood stem cell dose. This is calculated by dividing the absolute total nucleated cell dose in the harvest by the recipient’s weight in kilograms. When there is a large weight disparity between donor and recipient, there is a high risk of failure to achieve the minimum target total nucleated cell dose. However, lighter donors may be accepted providing that the weight disparity with the recipient is not unacceptable, and providing the donor is in good health and otherwise eligible to donate. This should always be discussed with the Transplant Centre. However, there are potential cell dose concerns if the donor’s weight is less than 70% of the recipient’s weight. The suggested figure of 70% comes from consultation with the UK bone marrow transplant community, rather than from any formal guidance document.

Similarly, to ensure recipient engraftment, it is vital that a PBSC collection contains a sufficient blood stem cell dose. As for bone marrow harvest, this is calculated by dividing the absolute blood stem cell dose in the apheresis product by the recipient’s weight in kilograms. As for bone marrow, lighter donors may be accepted providing that the Transplant Centre does not consider that there is too large a weight disparity with the recipient, and providing the donor is in good health and otherwise eligible to donate. As for bone marrow, there are potential cell dose concerns if the donor’s weight is less than 70% of the recipient’s weight. Again, the suggested figure of 70% comes from consultation with the UK bone marrow transplant community, rather than from any formal guidance document.

Adult donors weighing less than 30 kg may not be accepted under any circumstances, since the volume of the cell separator machine’s extracorporeal circuit would then exceed 15% of the donor’s total blood volume, with unacceptable risks of hypovolaemia and/or vasovagal issues.

Obesity makes it desirable to use more than a donor's weight to estimate their blood volume. Fat contains far less blood as a proportion of its weight than muscle. In obese individuals, the blood volume can be seriously overestimated from weight alone. Overestimating a donor's blood volume makes it more likely that they will have an adverse incident.

Donors who are overweight or obese tend to have more moderate to severe pain with PBSC donation. Bone marrow harvest is technically a considerably more difficult procedure in overweight donors. There is much evidence to support the concept that the morbidly obese in general (i.e. with a BMI >35) have a higher risk of premature death, anaesthetic complications and occult cardiovascular disease.

However, it is recognised that a high BMI does not always reflect obesity and body habitus and many high BMI donors may be fit and suitable to donate.

Reason for change:
Guidance has been updated to allow acceptance of donors under 50 kg, provided there is no unacceptable weight disparity between the donor and recipient.
Version details:

BM-DSG Edition 203 Release 61 (6 October 2026)