Testing errors within a transfusion service laboratory encompass a broad range of error types and can be defined in many ways. How such errors are defined influences their relative frequency as causes of serous adverse events.


Before discussing "testing errors," error needs to be defined and understood. Hofer et al. believe that medical errors should be defined in terms of failed processes that are clearly linked to adverse outcomes:

  • Hofer TP, Kerr EA, Hayward RA. What is an error? (Effective Clinical Practice,  Nov/Dec 2000; American College of Physicians website)

Besides understanding what errors are, it is important to remember that healthcare workers are reluctant to report errors unless the organization has a blame-free culture of error management.

As discussed earlier, RCA requires standardized terminology, including the need to have a common understanding of what constitutes "testing error" as a root cause. In the blood bank we are accustomed to referring to errors made by technologists when performing laboratory tests by the catchall phrase "technical errors" or "human technical errors", including errors of interpretation.


Regardless of how testing errors are categorized, adverse events caused  by technologists making mistakes when performing laboratory tests remain a significant source of serious adverse events. For example, the SHOT Annual Report 2003 includes 183 errors made in transfusion service laboratories involving errors in ABO and Rh typing,  antibody identification, as well as errors unrelated to laboratory testing. Example:

  • Case 18
    A BMS (lab technologist) not normally working in transfusion misread manual ABO group. 2 units ABO incompatible blood given before error realised. Patient died from injuries.
  • Case 19
    Uncrossmatched group specific blood requested. An inexperienced BMS misread manual group, checked by senior BMS but error not recognised. ABO incompatible blood given. Patient survived.
  • Case 27
    A 42 year old female patient underwent reconstructive surgery following mastectomy, following which she required urgent transfusion. Pretransfusion testing was carried out urgently by a BMS not normally working in transfusion. The patient?s Rh group was incorrectly determined as positive and Group O Rh positive blood was crossmatched and issued. The patient was aware that she was Rh negative and queried the group of the transfused blood, but was reassured by a nurse.
  • Case 30
    Blood was requested out of hours for a routine transfusion. The on-call BMS did not normally work in the transfusion laboratory. The antibody screen was positive, however the BMS wrongly interpreted it as due to ?non-specific IAT antibodies? despite a negative IAT control. He crossmatched and issued apparently compatible blood. The following day further investigations showed an anti-S and anti-Kpa. Two of the transfused units were S positive. The patient had a poor haemoglobin increment. The BMS was suspended from on-call duties.


Marx has outlined 4 types of overlapping conduct related to error: human error, negligence, reckless conduct, and intentional rule violations (examples shown are added by TraQ):

Marx D. Patient safety and the 'just culture': A primer for health care executives

Human error

Mistakes and lapses that have an inadvertent outcome, e.g.,

  • Technologist is distracted and inadvertently adds the incorrect reagent to a test, resulting in wrong results.


Failure to exercise the skill, care, and learning expected of a reasonably prudent healthcare practitioner. Negligent actions are different from "honest mistakes". Negligence involves preventable, harmful errors that fall below the standard expected of a reasonably careful and knowledgeable practitioner acting in a similar situation.

Legally, negligence can be proved only if certain conditions are met: (i) a duty of care was owed; (ii) the duty was breached; (iii) injury or loss occurred; and (iv) the breach caused the damage, e.g.,

  • Physician fails to order prenatal testing on pregnant woman throughout her pregnancy  and maternal antibody causes severe hemolytic disease in fetus

Reckless conduct (gross negligence)

Involves conscious disregard of a visible, significant risk, e.g.,

  • Nurse fails to check patient identity before hanging a unit of blood

Intentional rule violations

Intention to violate a known rule, procedure, or duty in the course of performing a task, e.g.,

  • Blood collector knows that samples must be labelled at the bedside but prelabels them in order to complete afternoon collections and leave work early.

As shown, these types of conduct overlap as the examples can fall into more than one category.


In Case A8, an informal but expanded investigation was performed (not a formal RCA). The cause of the transfusion reaction was identified as "human error" on the part of the student and supervising technologist, with the recognition that the process for training students and new staff to perform batch testing needed to be reviewed to identify how it could be improved.

Using MERS language, root causes perhaps would have been identified as 

  1. Active Errors (Human) -- Skill Based Behavior -- Slip -- code HSS
    • HSS definition: Failures in the performance of highly developed skills. An example could be a technologist adding drops of reagent to a row of test tubes and then missing a tube or computer entry error.

  2. Latent Errors -- Organizational -- Transfer of Knowledge -- code OK
    • OK definition: Failures resulting from inadequate measures taken to ensure that situational or site-specific knowledge or information is transferred to all new or inexperienced staff.

In terms of the types of conduct outlined by Marx, human error would seem to apply to both the student and supervising technologist. There was no reckless conduct or intentional rule violation. Was there negligence? What do you think?