Table 3.

Summary of studies examining the use of resistive index (RI) in AKI

Study (Reference)Renal RI/GroupStudy Notes
Healthy volunteers (20)0.60±0.07/Normal
Predicting AKI post-CPB (26)0.68±0.06/No AKI 1–5 d laterSingle-center, prospective, n=65
0.77±0.08/AKI without RRT 1–5 d laterRI was determined immediately after CPB
0.84±0.03/AKI requiring RRT 1–5 d laterPresence of AKI was assessed on days 1–5
An RI>0.74 had an AUC of 0.91 to predict AKI with 85% sensitivity and 94% specificity
Predicting AKI in septic shock (27)0.68±0.08/No AKI 5 d laterSingle-center, prospective, n=35
0.77±0.08/AKI 5 d laterRI was obtained within 24 h of ICU admission
Presence of AKI was assessed on day 5
AKI was defined as RIFLE stage 2 or greater (i.e., doubling of serum creatinine or greater)
An RI>0.74 predicted AKI with 78% sensitivity and 77% specificity
Predicting AKI in the ICU (28) (sepsis and trauma)0.66±0.08/No AKI 3 d laterSingle-center, prospective, n=58
0.80±0.08/AKI 3 d laterRI was obtained within 12 h of ICU admission
Presence of AKI was assessed on day 3
AKI was defined as stage 2 AKIN or greater (i.e., doubling of serum creatinine or greater)
An RI of 0.71 predicted AKI with an AUC of 0.91
Identifying prerenal azotemia (29)0.67±0.90/Prerenal azotemiaSingle-center, n=91
0.74±0.13/Non-ATN AKI (mostly HRS)An RI≥0.75 occurred in 91% of patients with ATN and 20% of patients with prerenal azotemia
0.85±0.60/ATN
Identifying prerenal azotemia (30)0.76±0.06/Prerenal azotemiaSingle-center, n=50
0.82±0.07/ATNAn RI≥0.75 had 91.3% sensitivity and 85.2% specificity to distinguish ATN from prerenal azotemia
Identifying prerenal azotemia/assessing severity (31)0.52–0.71/Prerenal azotemiaSingle-center, n=40
0.77–1.0/ATNDecreasing RI predicted renal recovery
Assessing severity (57)0.71 (0.62–0.77)/Transient AKISingle-center, n=51
0.82 (0.80–0.89)/Persistent AKIPersistent AKI was defined as AKI for >3 d
An RI>0.795 had 82% sensitivity and 92% specificity for persistent AKI
  • Values are expressed as mean ± SD. Numbers in parentheses are references. CPB, cardiopulmonary bypass; RRT, renal replacement therapy; AUC, area under the curve; ICU, intensive care unit; RIFLE, risk, injury, failure, loss, and end-stage kidney disease; AKIN, Acute Kidney Injury Network; ATN, acute tubular necrosis; HRS, hepatorenal syndrome.