Table 3.

Association of newer and traditional biomarker levels at time of AKI diagnosis with the primary outcome

Biomarker CutoffsPercent with the OutcomeaUnadjusted RR (95% CI)AUC (95% CI)Limited Adjustment RR (95% CI)bAUC (95% CI)Full Adjustment RR (95% CI)cAUC (95% CI)
Urine NGAL (ng/ml)
    Q1 (<18.3)10%Ref0.71 (0.64 to 0.77)Ref0.74 (0.67 to 0.81)Ref0.75 (0.68 to 0.81)
    Q2 (18.3 to 62.3)26%2.7 (1.1 to 6.4)1.9 (1.0 to 3.8)1.6 (0.9 to 2.80)
    Q3 (62.3 to 234.9)26%2.7 (1.1 to 6.4)1.9 (1.0 to 3.8)1.6 (0.9 to 2.8)
    Q4 (>234.9)55%5.7 (2.6 to 12.6)3.6 (1.9 to 6.7)2.6 (1.6 to 4.3)
Urine KIM-1 (ng/ml)
    Q1 (<1.5)16%Ref0.64 (0.57 to 0.72)Ref0.68 (0.60 to 0.75)Ref0.69 (0.61 to 0.76)
    Q2 (1.5 to 2.8)26%1.6 (0.8 to 3.2)1.6 (0.8 to 3.2)1.5 (0.8 to 3.1)
    Q3 (2.8 to 4.9)27%1.7 (0.8 to 3.4)1.7 (0.9 to 3.5)1.6 (0.8 to 3.2)
    Q4 (>4.9)47%2.9 (1.5 to 5.4)3.0 (1.6 to 5.5)2.8 (1.5 to 5.3)
Urine IL-18 (pg/ml)
    Q1 (<25.7)18%Ref0.63 (0.55 to 0.70)Ref0.66 (0.59 to 0.74)Ref0.68 (0.60 to 0.76)
    Q2 (25.7 to 69.8)26%1.5 (0.7 to 2.9)1.4 (0.7 to 2.7)1.3 (0.7 to 2.7)
    Q3 (69.8 to 178.1)27%1.5 (0.8 to 3.0)1.4 (0.7 to 2.7)1.3 (0.7 to 2.7)
    Q4 (>178.1)45%2.5 (1.4 to 4.6)2.5 (1.4 to 4.6)2.7 (1.4 to 5.0)
FeNa
    <1%27%Ref0.50 (0.42 to 0.57)Ref0.58 (0.50 to 0.67)Ref0.62 (0.54 to 0.70)
    1 to 2%35%1.3 (0.8 to 2.2)1.3 (0.8 to 2.1)1.2 (0.7 to 2.1)
    ≥2%25%1.0 (0.6 to 1.6)1.0 (0.6 to 1.7)1.0 (0.6 to 1.7)
FeUrea
    <35%29%Ref0.51 (0.48 to 0.55)Ref0.6 (0.52 to 0.67)Ref0.64 (0.56 to 0.72)
    35 to 50%11%0.4 (0.1 to 2.5)0.4 (0.1 to 2.7)0.4 (0.1 to 2.6)
    ≥50%29%1.0 (0.3 to 3.3)1.1 (0.3 to 3.7)1.1 (0.3 to 3.6)
Microscopy score
    014%Ref0.63 (0.54 to 0.71)Ref0.66 (0.57 to 0.75)
    124%1.6 (0.5 to 5.2)1.6 (0.5 to 5.2)N/Ad
    232%2.3 (0.8 to 6.8)2.3 (0.8 to 6.8)
    353%3.7 (1.2 to 11)3.5 (1.1 to 11)
  • Each biomarker listed was assessed individually in all models without combining biomarkers. All regression models shown were sufficiently calibrated with “goodness-of-fit” P values >0.1 by the Hosmer-Lemeshow method. AKI, acute kidney injury; RR, relative risk from log-binomial regression; CI, confidence interval; AUC, area under the receiver operating characteristic curve; NGAL, neutrophil gelatinase-associated lipocalin; KIM-1, kidney injury molecule-1; FeNa, fractional excretion of sodium; FeUrea, fractional excretion of urea; Ref, reference value.

  • a Percentage with the outcome within each quartile or group.

  • b Adjusted for age ≥65 years, body mass index, male gender, and non-Caucasian race. The AUC for this model alone was 0.58 (0.50 to 0.66).

  • c Adjusted for all covariates above plus baseline glomerular filtration rate, surgery before AKI, diabetes, and hypertension. The AUC for this model alone was 0.62 (0.54 to 0.70). By the DeLong test, AUCs were only significantly different between this model and the model with the addition of urine NGAL quartiles (P = 0.003).

  • d Full adjustment was not applicable for the urine microscopy score given only three actual occurrences for the primary outcome for the lowest (reference) score.