Number needed to biopsy ratio and diagnostic accuracy for melanoma detection

• Published in: Journal of the American Academy of Dermatology Vol. 83; no. 3; pp. 780 - 787
• Main Authors: Marchetti, Michael A., Yu, Ashley, Nanda, Japbani, Tschandl, Philipp, Kittler, Harald, Marghoob, Ashfaq A., Halpern, Allan C., Dusza, Stephen W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2020
• Subjects: Biopsy - methods; Biopsy - statistics & numerical data; Cross-Sectional Studies; Dermoscopy - statistics & numerical data; diagnostic accuracy; Early Detection of Cancer - methods; Early Detection of Cancer - statistics & numerical data; Humans; melanoma; Melanoma - diagnosis; Melanoma - mortality; Melanoma - pathology; melanoma positive predictive value; melanoma screening; melanoma sensitivity; melanoma specificity; NNB; number needed to biopsy; Predictive Value of Tests; Skin - diagnostic imaging; Skin - pathology; Skin Neoplasms - diagnosis; Skin Neoplasms - mortality; Skin Neoplasms - pathology; melanoma screening; diagnostic accuracy; NNB; HCP; melanoma sensitivity; number needed to biopsy; PPV; melanoma positive predictive value; melanoma; melanoma specificity
• ISSN: 0190-9622; 1097-6787
• DOI: 10.1016/j.jaad.2020.04.109

The number needed to biopsy (NNB) ratio for melanoma diagnosis is calculated by dividing the total number of biopsies by the number of biopsied melanomas. It is the inverse of positive predictive value (PPV), which is calculated by dividing the number of biopsied melanomas by the total number of biopsies. NNB is increasingly used as a metric to compare the diagnostic accuracy of health care practitioners. To investigate the association of NNB with the standard statistical measures of sensitivity and specificity. We extracted published diagnostic accuracy data from 5 cross-sectional skin cancer reader studies (median [min-max] readers/study was 29 [8-511]). Because NNB is a ratio, we converted it to PPV. Four studies showed no association and 1 showed a negative association between PPV and sensitivity. All 5 studies showed a positive association between PPV and specificity. Reader study data. An individual health care practitioner with a lower NNB is likely to have a higher specificity than one with a higher NNB, assuming they practice under similar conditions; no conclusions can be made about their relative sensitivities. We advocate for additional research to define quality metrics for melanoma detection and caution when interpreting NNB.