Table 3.

Incidence of Adverse Events in the Observation and Transfusion Groups per 100 Person-Years.

Adverse Event	Sample Size	At Least 1 Adverse Event	Total Adverse Events	At-Risk Time	Adverse Events/ 100 Person-Yr	Incidence Rate Ratio (95% CI)*	P Value
	no. of participants		no.	person-yr
Vaso-occlusive pain						0.41 (0.20–0.75)	0.004
Observation group	97	56	295	289	102.21
Transfusion group	99	32	126	304	41.58
Acute chest syndrome						0.13 (0.04–0.28)	<0.001
Observation group	97	24	41	289	14.35
Transfusion group	99	5	5	304	1.81
Priapism†						0.13 (0.03–0.55)	0.02
Observation group	52	7	10	158	6.65
Transfusion group	59	1	1	178	0.84
Symptomatic avascular necrosis of the hip						0.22 (0.05–0.85)	0.02
Observation group	97	6	6	289	2.25
Transfusion group	99	1	1	304	0.49
Headache						0.78 (0.39–1.57)	0.40
Observation group	97	30	93	289	32.34
Transfusion group	99	24	76	304	25.15
Blood-transfusion reaction						5.33 (1.67–23.52)	0.05
Observation group	31‡	1	1	90	1.66
Transfusion group	90§	15	24	277	8.85
Ferritin >1500 ng/ml						14.42 (5.41–875.17)	<0.001
Observation group	31‡	3	33	90	37.07
Transfusion group	90§	76	1479	277	534.70

^*The incidence ratio was calculated as the rate of adverse events per 100 person-years in the transfusion group divided by the rate of adverse events per 100 person-years in the observation group. The 95% confidence intervals were calculated with the use of the bootstrap method with 10,000 replications.

^†This event was documented in male participants only.

^‡A total of 31 participants who were randomly assigned to observation received one or more transfusions.

^§A total of 9 participants who declined transfusions were excluded from this analysis.