To improve diagnostic accuracy, the ABCD rule of lesion screening is widely used, which is based on asymmetry (A), border (B), color (C), and differential structure (D) measuring.
• A total dermatoscopic value (TDV) results from the calculation
TDV = A·1,3 + B·0,1 + C·0,5 + D·0,5
• This score contributes to the differentiation between benign and malignant lesions:
1,00 – 4,75 – benign skin lesion
4,75 – 5,45 – suspicious
More than 5,45 – melanoma
A – Asymmetry of Shape, Structure, and Color. The skin lesion is divided into four regions, and symmetry is inspected across the x or y-axis. If asymmetry is only by one axis, it gives 1 point, and if on both axes, there are 2 points calculated. So for shape, structure, and color, there can be 6 points maximum.
Border and Color
For measuring border irregularities, the lesion is divided into eight regions. If, in one particular region, the color ends strictly with the boundary of the lesion, there is one point. If the lesion color changes smoothly to skin color, then there are 0 points. So for B, there can be a maximum of 8 points.
For color, there can be as many points as many colors there can be found on the lesion. Usually, there are 6 primary colors, so total of 6 points for C.
Dermatological Structure D
There are five main structures noticed in lesions. No structures – smooth color – 1 point, net structure another 1 point, tree-like boundaries another 1 point, dots – 1 point, and globules 1 point. Total of 5 points can be. In some literature, there can be a diameter of lesion measured for D. If the width is more than 6 mm it can be stated as suspicious.
When looking at the Total Dermatological Value formula, there are evidence that the main criteria are Asymmetry. It is usually the main screening option. It is easy to inspect yourself using this methodology. If there is any concern, it is better to visit your doctor.