Table 2

Diagnostic performance characteristics of three different algorithms for ICD-10 code N17× using four different serum creatinine-based definitions of AKI as the reference standard

Diagnostic performance characteristics (95% CI)
Diagnostic coding algorithmDefinitionEmergency Department CohortHospitalised Cohort
All diagnosesAKIN Stage 1Sn=7.2 (6.6 to 8.0)Sn=21.8 (20.9 to 22.8)
Sp=99.9 (99.8 to 99.9)Sp=98.4 (98.2 to 98.5)
PPV=90.4 (87.2 to 92.8)PPV=74.2 (72.3 to 76.1)
NPV=86.2 (85.8 to 86.5)NPV=85.3 (84.9 to 85.6)
RIFLE RiskSn=30.4 (26.5 to 34.7)Sn=56.4 (53.2 to 59.7)
Sp=99.2 (99.1 to 99.3)Sp=96.0 (95.8 to 96.2)
PPV=33.8 (29.5 to 38.4)PPV=24.7 (22.8 to 26.6)
NPV=99.1 (99.0 to 99.2)NPV=98.9 (98.8 to 99.1)
RIFLE InjurySn=37.4 (32.1 to 43.1)Sn=61.6 (57.5 to 65.5)
Sp=99.1 (99.0 to 99.2)Sp=95.6 (95.4 to 95.8)
PPV=25.8 (21.9 to 30.2)PPV=17.3 (15.7 to 19.0)
NPV=99.5 (99.4 to 99.6)NPV=99.4 (99.3 to 99.5)
RIFLE FailureSn=30.2 (26.4 to 34.2)Sn=59.1 (55.9 to 62.3)
Sp=99.2 (99.2 to 99.3)Sp=96.1 (95.9 to 96.3)
PPV=37.3 (32.9 to 42.0)PPV=26.9 (25.0 to 28.9)
NPV=99.0 (98.9 to 99.1)NPV=99.0 (98.9 to 99.1)
 
Main diagnosis/most responsible diagnosisAKIN Stage 1Sn=4.1 (3.6 to 4.6)Sn=5.1 (4.6 to 5.7)
Sp=100.0 (99.9 to 100.0)Sp=99.9 (99.8 to 99.9)
PPV=94.7 (91.0 to 97.0)PPV=90.7 (87.4 to 93.2)
NPV=85.8 (85.4 to 86.1)NPV=82.9 (82.5 to 83.3)
RIFLE RiskSn=21.4 (17.9 to 25.3)Sn=18.7 (16.2 to 21.4)
Sp=99.6 (99.6 to 99.7)Sp=99.4 (99.3 to 99.5)
PPV=44.5 (38.2 to 51.0)PPV=42.5 (33.7 to 47.5)
NPV=99.0 (98.9 to 99.1)NPV=98.1 (98.0 to 98.3)
RIFLE InjurySn=27.9 (23.1 to 33.3)Sn=22.8 (19.5 to 26.4)
Sp=99.6 (99.6 to 99.7)Sp=99.3 (99.2 to 99.4)
PPV=36.1 (30.2 to 42.6)PPV=33.3 (28.7 to 38.1)
NPV=99.4 (99.3 to 99.5)NPV=98.9 (98.7 to 99.0)
RIFLE FailureSn=22.0 (18.7 to 25.7)Sn=22.9 (20.3 to 25.8)
Sp=99.6 (99.5 to 99.7)Sp=99.5 (99.5 to 99.6)
PPV=51.1 (44.6 to 57.5)PPV=54.4 (49.4 to 59.3)
NPV=98.9 (98.7 to 99.0)NPV=98.1 (98.0 to 98.3)
 
Admission diagnosisAKIN Stage 1n/aSn=15.8 (15.0 to 16.7)
Sp=99.2 (99.1 to 99.3)
PPV=81.6 (79.4 to 83.6)
NPV=84.5 (84.1 to 84.8)
RIFLE RiskSn=43.1 (39.9 to 46.4)
Sp=97.5 (97.3 to 97.6)
PPV=28.5 (26.2 to 31.0)
NPV=98.6 (98.5 to 98.8)
RIFLE InjurySn=48.3 (44.2 to 52.4)
Sp=97.2 (97.0 to 97.4)
PPV=20.5 (18.4 to 22.8)
NPV=99.2 (99.1 to 99.3)
RIFLE FailureSn=47.4 (44.2 to 50.6)
Sp=97.6 (97.5 to 97.8)
PPV=32.6 (30.2 to 35.2)
NPV=98.7 (98.6 to 98.8)
  • All values are presented as percentages (%).

  • To convert serum creatinine from μmol/l to mg/dl divide by 88.4.

  • AKI, acute kidney injury; ICD-10, International Classification of Diseases, tenth revision; NPV, negative predictive value; PPV, positive predictive value; Sn, sensitivity; Sp, specificity; n/a, not applicable.