How can you tell FUE donor site depletion?

Take a look at this photo. There is an area on the top that shows the normal density (click on the photo to enlarge) where hair was not removed hair by hair group as in the main donor area shows. It should be clear from this normal section of hair what a normal donor density looks like prior to an FUE being done.  Donor site density reduction occurs in every hair transplant regardless of the technique.  Depletion is used when the density reduction achieves a clinical state where there is less than adequate coverage for the donor area and as a result, one can either see-through it, or there is clearly less bulk present when the hair is grown out longer. I will discuss this below.

Donor site depletion is not necessarily a numbers issue. For example if one has 3500 FUE grafts removed from the donor area, is that number adequate to produce donor site depletion?  In some men with a coarse hair, 3500 removed FUE grafts may not cause visual loss of coverage for the donor area with hair that is 1-2cm long. Likewise, 3500 FUE grafts removed for someone with fine hair will find significant donor site depletion with hair that is 1-2cm long. For someone with an average hair weight, 3500 grafts may be a reasonable limit before one sees donor site depletion with hair that is 2cm long.

Some surgeons do strip surgeries which also deplete the donor area.  Assuming that there is no significant scar (less than 3mm wide) then the donor area stretches with removal of 3500 grafts.  Assuming that the area where the stretches is spread over the entire scalp, it impacts the scalp in the back of the head and that the stretch extends upward from the point where the strip was removed to all of the remaining untouched hair in the back of the head. If the person had a full Norwood Class 7 pattern of balding, the 3 inches of scalp remaining will have a reduction of density that is 84% of its original density or a 16% reduction in density.  The difference between the FUE surgery example and the strip surgery example would be in the uniformity of the donor site’s appearance. There would be no gaps in-between the follicular units in the strip scenario unlike the FUE scenario which clearly would have gaps rather than uniform stretching.

The two procedures are not really comparable because the surgeons often selectively remove the follicular units with more hair with FUE than the strip surgery (i.e. more 3-4 hair grafts).  So the person with 3500 FUE grafts harvested from the 3 inch high donor area most likely will lose more hair from the donor area than the person who had 3500 grafts from the strip surgery. It is the hair bulk that is left behind that determine if there is donor site depletion and this is an individual call for each patient who has had any hair transplant surgery. The patient in the picture could be donor site depleted with the standard of 1-2cm long hair or not. I personally would like to see his hair grown out to a length of 2cm and then make a value judgement.  Do you copy that?