Appendix-C-BV-Protocol

NHSN Biovigilance Component
Protocol v1.3.1
www.cdc.gov/nhsn

Appendix C. Adverse Reaction Severity and Imputability Definitions
Severity
An assessment of the degree to which the patient developed symptoms as a result of the adverse event.
Grade 1: Non-Severe
Medical intervention (e.g. symptomatic treatment) is required but lack of such would not result in
permanent damage or impairment of a bodily function.
Grade 2: Severe
Inpatient hospitalization or prolongation of hospitalization is directly attributable to the adverse
reaction, persistent or significant disability or incapacity of the patient occurs as a result of the
reaction, or a medical or surgical intervention is necessary to preclude permanent damage or
impairment of a body function.
Grade 3: Life-threatening
Major intervention required following the transfusion (e.g. vasopressors, intubation, transfer to
intensive care) to prevent death.
*Grade 4: Death
The recipient died as a result of the adverse transfusion reaction.
*Grade 4 should be used only if death is possibly, probably or definitely related to transfusion. If the
patient died of a cause other than the transfusion, the severity of the reaction should be graded as 1, 2 or
3 as appropriate given the clinical circumstances related to the reaction.

Imputability
An assessment of the relationship between the transfusion and the adverse event.
Definite: Conclusive evidence exists that the adverse event can be attributed to the transfusion.
Probable: Evidence is clearly in favor of attributing the adverse event to the transfusion.
Possible: Evidence is indeterminate for attributing the adverse event to the transfusion or an
alternate cause.
*Doubtful: Evidence is clearly in favor of attributing the adverse event to a cause other than the
transfusion.
*Ruled Out: Conclusive evidence beyond reasonable doubt that the adverse event can be attributed
to a cause other than the transfusion.
Not Determined: The relationship between the adverse event and the transfusion is unknown or not
stated.
*Adverse reactions for which imputability is doubtful or ruled out need not be routinely reported. These
categories are intended to be used when a reaction was initially thought to be transfusion-related but
additonal information revealed a non-transfusion related cause. However, facilities may use these
categories for their own purposes. For example, they can be used to keep an inventory of suspected
transfusion reaction investigations.

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June 2011