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Table 4 Test characteristics of the high sensitivity, high positive predictive value (PPV), and balanced algorithms for classifying type 1 diabetes compared to the reference standard in the validation cohort, stratified by age at diagnosis. Sensitivity, specificity, PPV and negative predictive value (NPV) are percentages with 95% confidence intervals. Cohen’s kappa coefficient represents agreement after agreement due to chance is removed (1.0 indicates perfect agreement) [31]. The “Type 1 Proportion” columns refer to the percentage of people in the cohort with diabetes classified as type 1 using each algorithm (“Calculated”) and the reference standard (“True”)

From: Development and validation of algorithms to classify type 1 and 2 diabetes according to age at diagnosis using electronic health records

AlgorithmTPFPFNTNSensitivitySpecificityPPVNPVKappaType 1 Proportion (%)
CalculatedTrue
High Sensitivity for Type 1: ratio of type 1 to type 2 codes ≥ 4, or at least 1 insulin prescription within 90 days
 All Ages412802477895.3 (84.2, 99.4)94.5 (93.8, 95.1)12.8 (9.3, 16.9)100.0 (99.8, 100.0)0.216.30.8
 Age < 20 years146021100.0 (76.8, 100.0)77.8 (57.7, 91.4)70.0 (45.7, 88.1)100.0 (83.9, 100.0)0.7148.834.1
 Age 20–39 years1941230090.5 (69.6, 98.8)88.0 (84.0, 91.2)31.7 (20.3, 45.0)99.3 (97.6, 99.9)0.4216.65.8
 Age ≥ 40 years823304457100.0 (63.1, 100.0)95.0 (94.4, 95.6)3.3 (1.4, 6.4)100.0 (99.9, 100.0)0.065.10.2
High PPV for Type 1: ratio of type 1 to type 2 codes ≥ 4, and multiple daily injections* with no other glucose-lowering medication prescription
 All Ages16027505837.2 (23.0, 53.3)100.0 (99.9, 100.0)100.0 (79.4, 100.0)99.5 (99.2, 99.6)0.540.30.8
 Age < 20 years8062757.1 (28.9, 82.3)100.0 (87.2, 100.0)100.0 (63.1, 100.0)81.8 (64.5, 93.0)0.6419.534.1
 Age 20–39 years601534128.6 (11.3, 52.2)100.0 (98.9, 100.0)100.0 (54.1, 100.0)95.8 (93.1, 97.6)0.431.75.8
 Age ≥ 40 years206469025.0 (3.2, 65.1)100.0 (99.9, 100.0)100.0 (15.8, 100.0)99.9 (99.7, 100.0)0.400.00.2
Optimized: ratio of type 1 to type 2 codes ≥ 4, and at least 1 insulin prescription within 90 days
 All Ages28915504965.1 (49.1, 79.0)99.8 (99.7, 99.9)75.7 (58.8, 88.2)99.7 (99.5, 99.8)0.700.70.8
 Age < 20 years12022785.7 (57.2, 98.2)100.0 (87.2, 100.0)100.0 (73.5, 100.0)93.1 (77.2, 99.2)0.8929.334.1
 Age 20–39 years127933457.1 (34.0, 78.2)97.9 (95.8, 99.2)63.2 (38.4, 83.7)97.4 (95.1, 98.8)0.585.25.8
 Age ≥ 40 years424468850.0 (15.7, 84.3)100.0 (99.8, 100.0)66.7 (22.3, 95.7)99.9 (99.8, 100.0)0.570.10.2
  1. Abbreviations: TP true positive, FP false positive, FN false negative, TN true negative
  2. *Multiple daily injections: defined as prescriptions for long-acting and short-acting insulin initiated in the same month
  3. See Appendix Table 6 for algorithms using renal function criteria