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ABCD Rule
[Stolz et al. Eur J Dermatol 1994]

To calculate the ABCD score, the 'Asymmetry, Border, Colors, and Dermoscopic structures' criteria are assessed semiquantitatively.

Each of the criteria is then multiplied by a given weight factor to yield a total dermoscopy score (TDS).

TDS values less than 4.75 indicate a benign melanocytic lesion, values between 4.8 and 5.45 indicate a suspicious lesion, and values of 5.45 or greater are highly suggestive of melanoma.

Asymmetry

To assess asymmetry, the melanocytic lesion is bisected by two 90º axes that were positioned to produce the lowest possible asymmetry score. If both axes dermocopically show asymmetric contours with regard to  shape, colors and/or dermoscopic structures, the asymmetry score is 2. 
If there is asymmetry on one axis only, the score is 1. If asymmetry is absent with regard to both axes the score is 0.

Border

The lesion is divided into eighths, and the pigment pattern is assessed. Within each 
one-eighth segment, a sharp, abrupt cut-off of pigment pattern at the periphery receives 
a score 1. In contrast, a gradual, indistinct cut-off within the segment receives a score 
of 0. Thus, the maximum border score is 8, and the minimum score is 0.

Color

Six different colors are counted in determining the color score: white, red, light brown, 
dark brown, blue-gray, and black. For each color present, add +1 to the score. 
White should be counted only if the area is lighter than the adjacent skin. 
The maximum color score is 6, and the minimum score is 1.

Dermoscopic structures

Evaluation of dermoscopic structures focuses on 5 structural features: network, structureless (or homogeneous) areas, branched streaks, dots, and globules. 
The presence of any feature results in a score +1 Structureless (or homogenous) areas must be larger than 10% of the lesion to be considered present. Branched streaks and dots are counted only when more than two are clearly visible. The presence of a single globule is sufficient for the lesion to be considered positive for globules.

Criterion Description Score Weight factor Asymmetry In 0, 1, or 2 axes; assess not only contour, but also colors and structures 0-2 X 1.3 Border Abrupt ending of pigment pattern at the periphery in 0-8 segments 0-8 X 0.1 Color Presence of up to 6 colors (white, red, light brown, dark brown, blue-gray, black) 1-6 X 0.5 Dermoscopic structures Presence of network, structureless or homogeneous areas, branched streaks, dots, and globules 1-5 X 0.5

Formula for TDS:
[ (A score x 1.3) + (B score x 0.1) + (C score x 0.5) + (D score x 0.5) ]

Total Dermoscopy Score (TDS) Interpretation <4.75 Benign melanocytic lesion 4.8-5.45 Suspicious lesion; close follow-up or excision recommended >5.45 Lesion highly suggestive of melanoma False-positive score (>5.45) sometimes observed in: Reed and Spitz nevus Clark nevus with globular pattern Congenital melanocytic nevus

A = 0 (x 1.3);
B = 8 (x0.1);
C = 2
[light-brown, dark-brown]
(x 0.5);
D = 2 
[network, globules]
(x 0.5)
--- TDS = 2.8 (benign) ---
Histopathologic diagnosis: Clark nevus

A = 1 (x 1.3);
B = 4 (x 0.1);
C = 3
[light-brown, dark-brown, black]
(x 0.5);
D = 2
[network, dots]
(x 0.5)
--- TDS = 4.2 (benign) ---
Histopathologic diagnosis: Clark nevus

A = 2 (x 1.3);
B = 5 (x 0.1);
C = 5
[light-brown, dark-brown, blue-gray, black, white]
(x 0.5);
D = 4
[homogeneous areas, streaks, dots, globules]
(x 0.5)
--- TDS = 7.6 (malignant) ---
Histopathologic diagnosis: melanoma

A = 0 (x 1.3);
B = 0 (x 0.1);
C = 2
[light-brown, dark-brown]
(x 0.5);
D = 2
[network, dots]
(x 0.5)
--- TDS = 2.0 (benign) ---
Histopathologic diagnosis: Clark nevus

A = 2 (x 1.3);
B = 3 * (x 0.1);
C = 4
[light-brown, dark-brown, blue-gray, black]
(x 0.5);
D = 4 
[network, streaks, dots, globules]
(x 0.5) 
--- TDS = 6.9 (malignant) ---
Histopathologic diagnosis: melanoma

A = 2 (x 1.3); 
B = 3 * (x 0.1);
C = 4
[light-brown, dark-brown, blue-gray, black]
(x 0.5);
D = 4 
[network, homogeneous areas, streaks, globules]
(x 0.5)
--- TDS = 6.9 (malignant) ---
Histopathologic diagnosis: melanoma