Some melanomas in their earliest stages may resemble blood blisters and reveal themselves as such if they continue to grow rather than disappearing in a reasonable time frame, states Know Cancer. Patients should not wait too long to seek medical treatment, as nodular melanomas are particularly aggressive.
Another potential indicator of whether or not a raised, dark red or black spot on the skin is a blood blister or a nodular melanoma is by pressing down on it with a finger. Much of the time, pressing on a blood blister causes the fluid to leave the blister, which in turn causes it to lighten in color. This does not occur with a nodular melanoma, states Dermnet.
Nodular melanomas can be particularly difficult to identify due to their appearance, which does not follow the usual ABCDE guidelines for identifying potentially cancerous spots on the skin. These guidelines stand for asymmetry, border irregularity, color, diameter of 1/4 inch and evolution, states WebMD. While the dark red or black color indicative of skin cancer and a state of evolution may be present, nodular melanomas are typically smaller in size, fairly symmetrical and do not have as irregular borders as other cancers. Doctors may instead use EFG to help identify a nodular melanoma, states Know Cancer. This stands for elevation, firm and growing. These traits can also help distinguish a nodular melanoma from a blood blister.