Table 1.

Example of early treatment trial in acute kidney injury^a

AKI etiology	Dichotomous outcome		Observed relative risk
	Intervention event rate	Control event rate
100% ATN + 0% non-ATN	14%	20%	0.7
90% ATN + 10% non-ATN	13.1%	18.5%	0.71
80% ATN + 20% non-ATN	12.2%	17%	0.72
70% ATN + 30% non-ATN	11.3%	15.5%	0.73
60% ATN + 40% non-ATN	10.4%	14%	0.74
50% ATN + 50% non-ATN	9.5%	12.5%	0.76
0% ATN + 100% non-ATN	5%	5%	1.0

Impact of changing the proportion of enrolled patients with true acute tubular necrosis (ATN) in a trial where a therapy reduces the relative risk (RR) of progressive kidney injury by 30% in patients with ATN, but has no effect on outcomes in the absence of ATN. We assume that 95% of non-ATN cases will respond to standard of care, and the acute kidney injury (AKI) will not progress. With these assumptions, the table shows the effect on observed RR with increasing proportion of non-ATN cases. Examples of calculation for 60% ATN + 40% non-ATN: Intervention rate: 60% (14%) + 40% (5%) = 10.4%. Control rate: 60% (20%) + 40% (5%) = 14%. RR = 10.4%/14% = 0.74.

^aTreatment administered at the time of clinical diagnosis of AKI by serum creatinine.