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Tests and diagnosis

By Mayo Clinic staff

Lice cement their eggs firmly onto the base of hair shafts, very close to the scalp. According to experts with the Centers for Disease Control and Prevention, nits found more than a quarter of an inch (6.5 millimeters) away from the scalp have either already hatched or aren't going to hatch. So simply finding nits isn't proof of an active infestation. The clearest sign is finding a living, moving louse. Combing wet hair with a fine-toothed comb is the best way to find this evidence.

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References
  1. Goldstein AO, et al. Pediculosis capitis. http://www.uptodate.com/home/index.html. Accessed April 25, 2011.
  2. Head lice: Frequently asked questions (FAQs). Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/lice/head/gen_info/faqs.html. Accessed April 25, 2011.
  3. Head lice: Treatment. Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/lice/head/treatment.html. Accessed April 25, 2011.
  4. Bedell DA, et al. Parasitology. In: Rakel RE. Textbook of Family Medicine. 7th ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/books/linkTo?type=bookPage&isbn=978-1-4160-2467-5&eid=4-u1.0-B978-1-4160-2467-5..50029-4. Accessed April 25, 2011.
  5. Schlossberg D. Arthropods and leeches. In: Goldman L, et al. Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/128370895-5/822078666/1492/1286.html#4-u1.0-B978-1-4160-2805-5..50385-2--cesec27_16133. Accessed April 26, 2011.
  6. Burkhart CN, et al. Fomite transmission in head lice. Journal of the American Academy of Dermatology. 2007;56:1044.
  7. Treating head lice. U.S. Food and Drug Administration. http://www.fda.gov/downloads/ForConsumers/ConsumerUpdates/UCM173526.pdf. Accessed April 27, 2011.
  8. Head lice: Prevention and control. Centers for Disease Prevention and Control. http://www.cdc.gov/parasites/lice/head/prevent.html. Accessed April 26, 2011.
  9. American Academy of Pediatrics. Clinical report — Head lice. Pediatrics. 2010;126:392.
DS00953 June 1, 2011

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