Up until today, the way diagnosis is made, are symptom-based. The specialist examines the skin condition and asks you a few questions. Based on his experience or knowledge he/she may be able to make an educated guess of skin condition you may have.
It is very important to understand that, up until today, it is very unlikely to have 100% guarantee that any diagnosis made in this manner is correct, basing it on the specialist opinion alone. Normally the easiest basic test your doctor or GP applies is the ABCDE rule. This is when the doctor tries to exclude that the particular lesion may be sinister.
Medicine is never an exact science and currently, the only known way to have the best degree of certainty that you have a correct diagnosis of each lesion on your body is the use of histological examinations. A histological examination is a detailed observation of the tissue of a living organism under the microscope. By looking at the microscope one can have the best chances to make the most accurate diagnosis currently possible.
To this day, the problem with histological examinations is that it is still impractical to perform on all the lesions on our body for two reasons:
→ Generally, because in order to extract the cell of the particular lesion a biopsy is required. Biopsies are rather invasive and are very likely to leave a scar. Also, it would be impractical to perform a biopsy on each lesion on our bodies because there are so many of them.
→ The real resources allocated (i.e costs) to performing a histological examination itself are relatively significant.
For these two reasons (scarring and costs), the doctor or specialist, normally makes an estimation of likely the lesions may be benign (harmless), alternatively how likely they maybe are something quite sinister. In case the perceived likelihood of the lesion to be nonbenign is relatively high, the doctor will opt to perform a punch biopsy to send the sample taken to the lab for a histological examination.
In this way, the diagnosis although not 100% accurate will have the best compromise in terms of invasiveness and costs, while hopefully still maintaining an acceptable degree of accuracy.