Welcome ICD-10-CM 2020! Do You Know the Code Set’s Secret Language?

know ICD-10-CM Official Guidelines terminology

As of Oct. 1, we are officially applying the 2020 ICD-10-CM code set. Get your diagnosis coding year off to a good start by refreshing your knowledge of some of the not-always-obvious terms essential to accurate claims: NEC, NOS, and, with.

If you want full details, check Section I. A of the FY2020 “ICD-10-CM Official Guidelines for Coding and Reporting.” And if you want to know more about ICD-10-CM 2020 changes, read our series with update highlights:

What Separates NEC From NOS?

Suppose you’re looking at documentation of an encounter, and the physician listed a specific diagnosis that ICD-10-CM does not provide a unique code for. Or suppose the documentation does not give enough information to choose a specific code and you need one that is “unspecified”? Which of these matches to the ICD-10-CM term NEC (not elsewhere classifiable) and which matches to NOS (not otherwise specified)?

The Official Guidelines, I.A.6 and I.A.9, clarify that NEC is the same as “other” or “other specified.” That means ICD-10-CM does not provide a code for the condition documented. So you should use an NEC, “other,” or “other specified” code for our first scenario above (specific diagnosis but no unique code).

The Official Guidelines go on to state that NOS is the same as “unspecified.” So you should use an NOS or unspecified code in our second scenario (not enough information to choose a more specific code). But watch out … if a category does not include an unspecified code, ICD-10-CM may indicate the “other specified” code represents both other and unspecified.

Tip: Also watch for these abbreviations and terms outside the code descriptors. For instance, new code D81.39 (Other adenosine deaminase deficiency) has “Adenosine deaminase [ADA] deficiency type 1, NOS” listed under it.

Are ‘And’ and ‘With’ More Than They Seem?

You might think you know what “and” and “with” mean, but ICD-10-CM shakes things up.

And: In Section I.A.14, the ICD-10-CM Official Guidelines state that “and” means either “and” or “or” in a code title. The example the Official Guidelines give is that subcategory A18.0- (Tuberculosis of bones and joints) includes tuberculosis of bones, tuberculosis of joints, and tuberculosis of bones and joints.

An American Academy of Pediatrics (AAP) article adds the example of using Z59.4 (Lack of adequate food and safe drinking water) for the diagnosis of a lack of adequate food with no mention of water in the documentation. The ICD-10-CM Alphabetic Index supports this by pointing to Z95.4 in the entry for “Lack of, adequate, food.”

With: Section I.A.15 of the Official Guidelines tells you to interpret “with” or “in” to mean “associated with” or “due to.” This rule applies when you see the term in a code title, the Alphabetic Index, or a Tabular List instructional note.

The point is that codes using those terms presume a causal relationship, and you should code them as related even if the provider doesn’t state there is a link.

There are exceptions to the rule:

  • If the documentation states the conditions are not related, do not code them as related.
  • If another guideline states certain conditions require a documented link, code them as related only when you have the required documentation.

What About You?

Want more tips? Head to our blog post covering Excludes 1, “code first,” and “use additional code” notes. What terms from ICD-10-CM make you feel like you know a secret language?


Deborah works on a wide range of TCI SuperCoder projects, researching and writing about coding, as well as assisting with data updates and tool development for our online coding solutions. Since joining TCI in 2004, she’s covered the ins and outs of coding for radiology, cardiology, oncology and hematology, orthopedics, audiology, and more.

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