Table 2.
Test Characteristics of Novel Biomarkers and Standard Diagnostic Markers*
| Biomarker and Cutoff Value | Sensitivity |
Specificity |
Positive Likelihood Ratio† (95% CI) | Negative Likelihood Ratio† (95% CI) | Positive Predictive Value | Negative Predictive Value | AUC (95% CI) | ||
|---|---|---|---|---|---|---|---|---|---|
| Value (95% CI) | Patients, n/n‡ | Value (95% CI) | Patients, n/n§ | ||||||
| NGAL | |||||||||
| 85 μg/g | 0.93 (0.78–0.99) | 28/30 | 0.98 (0.97–0.99) | 594/605 | 51.33 (28.36–92.91) | 0.07 (0.02–0.26) | 0.737 | 0.996 | 0.948 (0.881–1.000) |
| 130 μg/g | 0.90 (0.73–0.98) | 27/30 | 0.995 (0.99–1.00) | 602/605 | 181.50 (58.33–564.71) | 0.10 (0.03–0.29) | 0.900 | 0.995 | |
| NAG | |||||||||
| 1.0 U/g | 0.87 (0.69–0.96) | 26/30 | 0.32 (0.29–0.36) | 196/605 | 1.28 (1.10–1.49) | 0.41 (0.16–1.03) | 0.059 | 0.980 | 0.713 (0.618–0.809) |
| 4.5 U/g | 0.70 (0.51–0.85) | 21/30 | 0.63 (0.59–0.67) | 383/605 | 1.91 (1.48–2.47) | 0.47 (0.27–0.82) | 0.087 | 0.977 | |
| α1-Microglobulin | |||||||||
| 10 mg/g | 1.00 (0.88–1.00) | 30/30 | 0.53 (0.49–0.57) | 318/604 | 2.11 (1.94–2.30) | 0 (0–0.20) | 0.095 | 1.00 | 0.887 (0.840–0.934) |
| 35 mg/g | 0.80 (0.61–0.92) | 24/30 | 0.81 (0.77–0.84) | 487/604 | 4.13 (3.24–5.26) | 0.25 (0.12–0.51) | 0.173 | 0.987 | |
| α1-Acid glycoprotein | |||||||||
| 10 mg/g | 0.97 (0.83–1.00) | 29/30 | 0.48 (0.44–0.52) | 292/604 | 1.87 (1.69–2.07) | 0.07 (0.01–0.47) | 0.087 | 0.996 | 0.832 (0.772–0.893) |
| 21 mg/g | 0.87 (0.69–0.96) | 26/30 | 0.61 (0.57–0.65) | 367/604 | 2.21 (1.86–2.62) | 0.22 (0.09–0.55) | 0.099 | 0.989 | |
| Creatinine | |||||||||
| 124 μmol/L (1.4 mg/dL) | 0.93 (0.78–0.99) | 28/30 | 0.75 (0.71–0.78) | 451/602 | 3.72 (3.15–4.40) | 0.09 (0.02–0.34) | 0.187 | 0.995 | 0.921 (0.865–0.978) |
| 221 μmol/L (2.5 mg/dL) | 0.77 (0.58–0.90) | 23/30 | 0.93 (0.90–0.95) | 559/602 | 10.73 (7.57–15.22) | 0.25 (0.13–0.48) | 0/348 | 0.987 | |
| Fractional excretion of sodium | |||||||||
| 1.0% | 0.80 (0.61–0.92) | 24/30 | 0.44 (0.37–0.52) | 86/194 | 1.44 (1.15–1.79) | 0.45 (0.22–0.94) | 0.162 | 0.943 | 0.708 (0.611–0.806) |
All patient groups were used to calculate test characteristics for all markers except fractional excretion of sodium. We tested NGAL and NAG levels in 635 patients, α1-microglobulin and α1-acid glycoprotein levels in 634 patients, and creatinine levels in 632 patients. We measured fractional excretion of sodium only in the 244 patients with abnormal kidney function (acute kidney injury, chronic kidney disease, or prerenal azotemia). AUC = area under the receiver-operating characteristic curve; NAG = N-acetyl-β-D-glucosaminidase; NGAL = neutrophil gelatinase–associated lipocalin.
The likelihood ratio is the ratio of posttest odds to pretest odds corresponding to a test result. As such, it indicates the effect of a test result on the odds (or, equivalently, the probability) of a disease. A very large likelihood ratio or a likelihood ratio close to zero denotes a very good test; a likelihood ratio close to 1.0 indicates a poor test. The positive likelihood ratio is the likelihood ratio after a positive test result. The negative likelihood ratio is the likelihood ratio after a negative test result.
Patients with acute kidney injury who tested positive/all patients with acute kidney injury.
Patients without acute kidney injury who tested negative/all patients without acute kidney injury.