73 THE VALUE OF TELEDERMOSCOPY TO THE EXPERTISE OF GPS DIAGNOSING SKIN DISORDERS 2017, July 2017 – June 2018), and did not perform any consultation before January 2015. Unexperienced GPs were excluded in this study. The pre-diagnosis of the GP was compared with the diagnosis of the TD on the group level of the ICD-10 codes. Examples of group levels included are among others: C43-C44 Melanoma and other malignant neoplasms of skin, D00-D09 In situ neoplasms, D10-D36 Benign neoplasms, L20-L30 Dermatitis and eczema. The ICD-10 diagnosis of the TD was considered as the golden standard for the diagnosis confirmation. Statistical analyses The total percentage of cases a GP correctly diagnosed is calculated as the number of confirmed diagnosed GP cases by TD divided by the number of obtained teledermoscopy cases minus the number of patients for which the TD did not provide a diagnosis. To assess the surplus value of continuing use of teledermoscopy, the GP sensitivity and GP’s positive predictive value (PPV) in diagnosing skin disorders were calculated overall (total) and on the ICD-10 diagnosis group level for three subsequent years. The 95% confidence intervals (CI) of the PPV was calculated according to the Wilson score interval method without a correction for continuity [9]. The 2x2 table in Table 4.1 shows the formulas used to calculate the PPV for each diagnosis category separately. The PPV was calculated as the proportion of consultations where the ICD-10 code was present according to the pre-diagnosis of the GP and confirmed by the TD divided by the total number of diagnoses scored within this group ICD-10 code by the GP. The sensitivity was calculated as the number of cases where the ICD-10 prediagnosis of the GP was confirmed by the TD divided by the total number of diagnoses scored within this group based on the ICD-10 codes of the TD. Table 4.1: 2x2 table to calculate sensitivity and positive predictive value. Diagnosis TD (golden standard) Diagnosis confirmed with ICD-10 code of TD Diagnosis not confirmed with ICD-10 code of TD Diagnosis GP Diagnosis present according to ICD-10 pre-diagnosis of GP a b Diagnosis absent according to ICD-10 pre-diagnosis of GP c d a = True positives, Diagnosis present according to ICD-10 pre-diagnosis of GP and confirmed by TD. b = False positives, Diagnosis present according to ICD-10 pre-diagnosis of GP and not confirmed by TD. c = False negatives, Diagnosis absent according to ICD-10 pre-diagnosis of GP and confirmed by TD. d = True negatives, Diagnosis absent according to ICD-10 pre-diagnosis of GP and not confirmed by TD. Positive predictive value (PPV) of GP = a / (a+b) Sensitivity of GP = a / (a+c) 4
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