Grading Acanthosis Nigricans Using a Smartphone and Color Analysis: A Novel Noninvasive Method to Screen for Impaired Glucose Tolerance and Type 2 Diabetes

The objective of this study was to develop ANcam, a novel method for identifying acanthosis nigricans (AN) using a smartphone camera and computer-aided color analysis for noninvasive screening of people with impaired glucose tolerance (IGT). Adult and juvenile participants with or without diagnosed type 2 diabetes were recruited in Trinidad and Tobago. After obtaining informed consent, participants’ history, demographics, anthropometrics, and A1C were collected and recorded. Three subject-matter experts independently graded pictures of the posterior neck and upper back using the ANcam smartphone application and Burke methods. A correlation matrix investigated 25 color channels for association with hyperpigmentation, and the diagnostic thresholds were determined with a receiver operating characteristic curve analysis. For the 227 participants with captured images and A1C values, the cyan/magenta/yellow/black (CMYK) model color channel CMYK_K was best correlated with IGT at an A1C cut-off of 5.7% [39 mmol/mol] (R = 0.45, P <0.001). With high predictive accuracy (area under the curve = 0.854), the cut-off of 7.67 CMYK_K units was chosen, with a sensitivity of 81.1% and a specificity of 70.3%. ANcam had low interrater variance (F = 1.99, P = 0.137) compared with Burke grading (F = 105.71, P <0.001). ANcam detected hyperpigmentation on the neck at double the self-reported frequency. Elevated BMI was 2.9 (95% CI 1.9–4.3) times more likely, elevated blood pressure was 1.7 (95% CI 1.2–2.4) times more likely, and greater waist-to-hip ratio was 2.3 (95% CI 1.4–3.6) times more likely with AN present. ANcam offers a sensitive, reproducible, and user-friendly IGT screening tool to any smartphone user that performs well with most skin tones and lighting conditions.