Summary of findings 4. Plasma‐derived C1 esterase inhibitor compared with placebo or active control for preventing hereditary angioedema attacks.

pdC1‐INH compared with placebo or active control for preventing HAE attacks
Patient or population: children or adults with Types I or II HAE Settings: outpatient setting Intervention: pdC1‐INH Comparison: placebo
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	No of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with placebo	Risk with pdC1‐INH
Risk of HAE attacks (during follow‐up)	Study population		N/A	N/A	N/A	Outcome not reported
	N/A	N/A
Change in number of HAE attacks (per week)	Study population		—	71 (1)	⊕⊕⊝⊝ Lowa	—
	The number of HAE attacks per week in the control group was 0.9	The number of HAE attacks per week in the intervention group was 0.53 attacks lower (0.58 lower to 0.48 lower)
Mortality (during follow‐up)	Study population		N/A	N/A	N/A	No deaths reported
	N/A	N/A
Serious adverse events (during follow‐up)	Study population		RR 0.54 (0.09 to 3.10)	71 (1)	⊕⊝⊝⊝ Very lowb	—
	53 per 1000	29 per 1000 (5 to 164)
Quality of life Angioedema Quality of Life Score (lower score is better) (during follow‐up)	Study population		—	31 (1)	⊕⊕⊝⊝ Lowa	—
	The mean change in quality of life in the control group was −6.86	The mean change in quality of life in the intervention group was 3.49 points lower (10.86 lower to 3.88 higher)
Disability (any validated scale) (during follow‐up)	Study population		N/A	N/A	N/A	Outcome not reported.
	N/A	N/A
Adverse events (during follow‐up)	Study population		RR 1.05 (0.78 to 1.42)	71 (1)	⊕⊕⊝⊝ Lowa	—
	561 per 1000	589 per 1000 (438 to 797)
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; HAE: hereditary angioedema; N/A: not applicable; pdC1‐INH: plasma‐derived C1 esterase inhibitor; RR: risk ratio.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate. The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited. The true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate. The true effect is likely to be substantially different from the estimate of effect.

^aDowngraded two levels for imprecision.
^bDowngraded three levels for imprecision.