Writing in the Journal of Family Practice, Dr. Barbara Walker notes, "During my medical training and years in the military, I have seen patients who suffered prolonged itching because they had no microscopic confirmation of scabies, but who cleared quickly with treatment after a skin biopsy identified scabies."
"This," she said, "has given me a short fuse for treating empirically in my own clinics."

Bottom line—if you think you have scabies, it may be a good idea to ask your doctor to skip the scrape (to find the critters), and go right to treatment, which at the moment is permethrin.
Also, make sure you treat any sexual partners, as well as anyone else who lives in your household.