Within ICD-9-CM, you may select codes defined as “Not Otherwise Specified” (NOS) when there isn’t enough documentation to select a more specific code. In other words, a deficiency in documentation prevents you from coding to a higher level of specificity.
NOS codes are never favored, and claims submitted with such diagnoses may be rejected for lack of medical necessity and/or specificity. When possible, you may wish to ask the documenting provider for additional information and/or to append the record, so that a more precise diagnosis may be selected.
Codes defined as “Not Elsewhere Classifiable” (NEC) may be selected when specific information is documented for the diagnosis, but there isn’t an existing ICD-9-CM code to report it. In this case, the ICD-9-CM manual—not the documentation—lacks additional specificity.

John Verhovshek
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John Verhovshek, MA, CPC, is a contributing editor at AAPC. He has been covering medical coding and billing, healthcare policy, and the business of medicine since 1999. He is an alumnus of York College of Pennsylvania and Clemson University.

No Responses to “ICD-9-CM: NOS vs. NEC”

  1. Pamela Martinez, CPC says:

    Good information and just wondering if the translation looks the same when moving into the ICD-10 coding arena. There will certainly be the same circumstance occur which necessitated this coding option be available in I-9 in the first place.

  2. SHABNA says:

    What would be the ICD 10 code for dehydration due to salmonella infection?? Will we consider NEC or NOS