Summary of findings 3. C1 esterase inhibitor compared with placebo or active control for preventing hereditary angioedema attacks.

C1‐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: C1‐INH(SC) 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 C1‐INH(SC)
Risk of HAE attacks (during follow‐up)	Study population		RR 0.29 (0.16 to 0.50)	43 (1)	⊕⊕⊝⊝ Lowa	—
	810 per 1000	24 per 1000 (0 to 162)
Change in number of HAE attacks (per week)	Study population		—	45 (1)	⊕⊕⊝⊝ Lowa	—
	The mean number of HAE attacks per week in the control group was 0.93	The mean number of HAE attacks per week in the intervention group was 0.81 lower (0.98 lower to 0.64 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 0.34 (0.01 to 8.14)	44 (1)	⊕⊝⊝⊝ Very lowb	—
	23 per 1000	8 per 1000 (0 to 187)
Quality of life standardised mean difference (lower is better) (during follow‐up)	Study population		—	36 (1)	⊕⊕⊝⊝ Lowa	—
	The mean change in quality of life in the control group was −0.87 units	The mean change in quality of life in the intervention groups was 0.29 units lower (0.76 lower to 0.18 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 1.03 (0.84 to 1.27)	44 (1)	⊕⊕⊕⊝ Moderatec	—
	663 per 1000	683 per 1000 (557 to 842)
*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). C1‐INH(SC): subcutaneous C1 esterase inhibitor; CI: confidence interval; HAE: hereditary angioedema; N/A: not applicable; 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.
^cDowngraded one level for imprecision.