The 2-sample rule (check group)

Blood Bank must ensure that there are TWO distinct samples from a patient. The same blood group must be present in both samples.If Blood Bank have seen the patient before, they should have a historic blood group registered on the Laboratory Information System (LIMS). In this instance, then only one group and save/X-match sample is required as per normal protocol. 

If the patient has no previous records in Blood Bank then you MUST repeat the group and save/X-match with a second sample. You must use a specific request form & sample bottle that will be provided by Blood Bank. 

This national recommendation is based on the evidence from:

• the BEST studies as referenced in the British Society of Haematology guidelines for pre-transfusion compatibility procedures in blood transfusion laboratories
• National data from the incorrect blood component transfused (IBCT) and the near miss chapters in recent Serious Hazards of Transfusions (SHOT) reports (SHOT, 1996 to 2010); 386 cases of wrong blood in tube (WBIT) were reported as near misses in 2010
• Local data confirms an unacceptable number of WBIT cases among patients where it can be detected due to having a historical group on record

Why is this rule being introduced?

Wrong blood in tube (WBIT) is a ‘never event’; it should never happen. However, on occasions, it does. The consequences of transfusing somebody with blood of the incorrect blood group is very serious and can lead to death. 

In the 6 months prior to implementation, there were four WBIT incidents within Barnsley Hospital NHS Foundation Trust. Two of which would have resulted in a major ABO incompatible transfusion if blood products had been requested. 

WBIT is a SHOT (Serious Hazards of Transfusion) reportable incident. The two-sample rule is a national guideline to improve patient safety when receiving transfusions. It has been adopted by the majority of NHS Trusts across the UK.

How does the two-sample rule work?

If the patient is not known to Blood Bank, then the two-sample rule is invoked. The two samples must come from separate venepuncture events and ideally should be carried out by two different staff members. 

A specific request form and sample will be issued by the laboratory. It should be collected from the Blood Bank upon delivery of the 1st group and save samples. This is the case in urgent situations or as required for routine requests. 

If a cross-match request - or group & save request - with clinical details implying that the patient will be undergoing surgery within the next 24 hours is received, and this is the first time Blood Bank has seen the patient. Then Blood Bank will notify the clinical area informing them that a ‘check group’ is required. It is then the responsibility of clinical staff to organise collection of this sample bottle.

It is not acceptable to take two samples at one venepuncture event and send them to Blood Bank on separate request forms. This will not negate the possibility of WBIT.

How will I know if a second sample is required?

If you are unsure if Blood Bank already has a historic blood group, clinical staff can check ICE for previous requests. Staff can also contact the laboratory to confirm.

What happens in an emergency situation?

If blood is required in an emergency such as, major haemorrhage protocol activation, the two-sample rule will still apply. 

However, the Blood Bank will only be able to issue Group O red cell products and AB plasma products in the absence of a check group sample. It is the responsibility of clinical staff to organise collection of the ‘check group’ bottle. 

Blood will be issued as per the MH protocol and will not be delayed.

Why can’t I use one of our own bottles?

The 2 sample rule needs to involve two separate venepuncture events. ‘Check Group’ request forms and bottles are specially labelled by the transfusion laboratory and are signed for upon collection by clinical staff. 

This is to assure the laboratory:

1. That the second venepuncture event involves a different sample.
2. That clinical staff are not obtaining two groups and save samples from the same venepuncture site at the same time and labelling them with different times.

These steps are in place solely for patient safety.

Check groups are there for patient safety and follow the same strict labelling, zero tolerance policy as for normal group and screens – NO EXCEPTIONS

This webpage was reviewed and updated by Mark Taplin, Blood Transfusion Manager, 22nd February 2024