Underlying causes: Conventions for ICD-10

Editor’s note: This article is part one of a three-part series. Part one addresses ICD-10-CM coding conventions, such as Excludes notes and etiology/manifestation coding conventions. Part two will focus on how general coding guidelines for ICD-10 apply to the coding of underlying conditions and their manifestations. Part three will discuss chapter-specific guidelines.

by Joel Moorhead, MD, PhD

Assigning codes based on underlying conditions will not be a new concept when we move to ICD-10. Underlying causes are integral to the structure of ICD-9. The ICD-9-CM Official Guidelines for Coding and Reporting, Section I.A.6, notes that certain conditions “have both an underlying etiology and multiple body system manifestations due to the underlying etiology,” and that coders should sequence first the underlying condition for these conditions. One aspect of the increased specificity of ICD-10-CM codes is the expanded detail in code descriptions within disease categories for these underlying conditions.

To understand how to code underlying conditions using the new code set, let’s take a look at how Excludes notes in ICD-10-CM address chronic obstructive pulmonary disease and acute bronchitis in a patient with underlying asthma.

Excludes notes

ICD-10-CM has two types of Excludes notes. In ICD-10-CM, an Excludes1 note corresponds with what today’s ICD-9 Excludes note indicates: The excluded code is independent of and cannot be used with the code noted above the Excludes note in the ICD-9 Manual. The excluded code conflicts with, is inherent to, or is unnecessary for full identification of the condition being coded. For example, you could not code the congenital and acquired forms of a condition together.

ICD-9 Section I.A.4 notes that some excluded terms can be used together with excluded codes, as when different listings code fractures of different bones.

However ICD-10-CM includes the designation of an Excludes2 note. The excluded code is independent of the code noted above the Excludes note. However, you may assign codes for both conditions when the patient has both conditions and coding of both conditions is appropriate according to coding guidelines. Some examples follow.

Chronic obstructive pulmonary disease, acute bronchitis, and asthma

Let's look at the coding of acute exacerbation of chronic obstructive pulmonary disease (COPD), acute bronchitis, and acute exacerbation of asthma under ICD-9. Coding Clinic, third quarter, 2006, p. 20, advises assigning code 491.22 (obstructive chronic bronchitis with acute bronchitis) and code 493.22 (chronic obstructive asthma with [acute] exacerbation) for the documented conditions.

The combination of these conditions has caused some coding confusion because an Excludes note under ICD-9 Category 491 (chronic bronchitis) indicates that Category 491 excludes chronic obstructive asthma (code 493.2). Likewise, an Excludes note under Subcategory code 493.2 indicates that Subcategory code 493.2 excludes chronic obstructive bronchitis (codes 491.20–491.22).

Note that ICD-9 Chapter-specific guidelines for COPD, asthma, and bronchitis (Sections I.C.8.a. and I.C.8.b.) take up a full column of the ICD-9 Official Guidelines for Coding and Reporting.

In contrast, the corresponding ICD-10-CM Chapter-specific guideline (Section I.C.10.a) addressing COPD and asthma is one short paragraph.

As in the ICD-9-CM Official Guidelines for Coding and Reporting, this section in ICD-10-CM notes that an acute exacerbation is not equivalent to an infection superimposed on a chronic condition.

ICD-9 listings 491.21 (obstructive chronic bronchitis with exacerbation) and 493.22 (chronic obstructive asthma with [acute] exacerbation) both map to ICD-10-CM listing J44.1 (COPD with exacerbation).

ICD-9 codes 491.22 (obstructive chronic bronchitis with acute bronchitis) and 493.21 (chronic obstructive asthma with status asthmaticus) map to ICD-10-CM listing J44.0 (COPD with acute lower respiratory infection). An Excludes2 note under code J44.1 excludes COPD with acute bronchitis (code J44.0). The ICD-10-CM Official Guidelines for Coding and Reporting permit the reporting of code J44.0 with J44.1, when both conditions are present.

An additional instructional note under ICD-10-CM Category J44 states that you should also report the type of asthma (code J45.-), if applicable.

An Excludes2 note under Category J45 (asthma) excludes:

  • Asthma with COPD
  • Chronic asthmatic (obstructive) bronchitis
  • Chronic obstructive asthma

The ICD-10-CM official guidelines would then permit coders to report a J45 code with a J44 code when both conditions are present. However, an Excludes1 note under Category J44 clearly states you cannot report chronic bronchitis not otherwise specified (NOS) (code J42) and emphysema without chronic bronchitis (code J43.-) together with J44 codes.

The brevity of the ICD-10-CM Chapter-specific guideline in this section seems to herald the creation of self-explanatory listings for these conditions that require little additional guidance. Coding Clinics will probably have something to say about this common combination of conditions after ICD-10 launches in 2013, but for now the draft guidelines appear relatively clear.

Complications of gastric surgery

ICD-10-CM brings greater clarity to the coding of another condition in which Excludes notes apply—malabsorption of nutrients following gastric surgery.

After gastric bypass surgery, it’s relatively common for patients to experience nutritional deficiencies, which lead to complications. Let's say you are coding a case in which the attending physician documents dumping syndrome and osteoporosis due to calcium malabsorption complicating gastric bypass surgery. You find dumping syndrome under postgastric surgery syndromes (code 564.2) in ICD-9-CM, and you’ll find the following Excludes note:

Malnutrition following gastrointestinal surgery (579.3)

ICD-9 provides no specific guidance on what type of Excludes note this is. When you look up code 579.3 (other and unspecified post-surgical malabsorption) there is no note excluding code 564.2. You conclude that the Excludes note under listing 564.2 may mean that you can code both conditions together when both are present, lacking any definitive evidence to the contrary. Perhaps ICD-10 will bring some needed clarity to this coding situation.

ICD-9 listing 564.2 maps to ICD-10-CM code K91.1 (postgastric surgery syndromes), which is not followed by any Excludes notes. ICD-9 code 579.3 maps to ICD-10-CM listing K91.2 (postsurgical malabsorption, not elsewhere classified). An Excludes1 note beneath ICD-10-CM code K91.2 excludes postsurgical malabsorption osteoporosis (code M81.3). You discover that the ICD-10-CM draft Manual does not contain code M81.3, but code M81.8 includes “postsurgical malabsorption osteoporosis without current pathological fracture.”

So ICD-10 provides a specific code for postsurgical malabsorption osteoporosis (M81.8 in the draft manual). It seems likely that the final version of ICD-10-CM will prohibit coding M81.8 (postsurgical malabsorption osteoporosis) with K91.2 (postsurgical malabsorption). This seems reasonable because the concept of “postsurgical malabsorption” is included in the more specific code M81.8 (postsurgical malabsorption osteoporosis). ICD-10-CM provides more specific listing titles for other more common manifestations of underlying causes as well, as illustrated by the ICD-10 coding of diabetes mellitus and its manifestations.

Etiology/Manifestation coding conventions

Section I.A.6 of the ICD-9 official guidelines recognizes that the most commonly used codes combining an underlying etiology with manifestation are listed under ICD-9 Category 250.xx (diabetes mellitus). The most commonly used underlying etiology codes in ICD-10-CM will likely be diabetes codes as well. ICD-10-CM includes some new combination codes to identify diabetic complications previously grouped under ICD-9 subcategory 250.8 (diabetes with other specified manifestations).

ICD-10-CM subdivides codes for diabetes mellitus into three categories:

  • Type I diabetes mellitus (E10)
  • Type II diabetes mellitus (E11)
  • Other specified diabetes mellitus (E13)

Inexplicably, there is no Category E12.

ICD-10-CM does not distinguish between controlled and uncontrolled diabetes. For principal diagnosis selection it’s important to note that the chapter-specific coding guidelines state that diabetes mellitus codes are sequenced based on the reason for a particular encounter (Section I.C.4.a.). ICD-9 subcategory 250.8 (diabetes with other specified manifestations) maps to Type I, Type II, and other specified diabetes mellitus with the following:

  • Diabetic neuropathic arthropathy (E10.610, E11.610, E13.610)
  • Other diabetic arthropathy (E10.618, E11.618, E13.618)
  • Diabetic dermatitis (E10.620, E11.620, E13.620)
  • Diabetic foot ulcer (E10.621, E11.621, E13.621)
  • Other skin ulcer (E10.622, E11.622, E13.622)
  • Other skin complication (E10.628, E11.628, E13.628)
  • Periodontal disease (E10.630, E11.630, E13.630)
  • Other oral complication (E10.638, E11.638, E13.638)
  • Hypoglycemia without coma (E10.649, E11.649, E13.649)
  • Hyperglycemia (E10.65, E11.65, E13.65)
  • Other specified complication (E10.69, E11.69, E13.69)

A surprising omission from this list is a specific code for diabetes mellitus with osteomyelitis.

“ICD-9-CM assumes a relationship between diabetes and osteomyelitis when both conditions are present, unless the physician has indicated in the medical record that the acute osteomyelitis is totally unrelated to the diabetes,” according to Coding Clinic, first quarter, 2004, pp. 14–15.

A fairly safe prediction might be that CMS will expand ICD categories E10, E11, and E13 in the future to include this specific complication, which would probably map to diabetes with other specified complication (E10.69, E11.69, E13.69) in the current ICD-10-CM draft code set.

The Etiology/Manifestation section in the ICD-10-CM official guidelines (Section I.A.13.) cites “dementia in Parkinson’s disease” as an example illustrating this convention. Sequence first the underlying condition code, Parkinson’s disease (G20). Then follow this with a code reporting a secondary diagnosis, a manifestation code from category F02 (dementia in other diseases classified elsewhere).

Editor’s Note: This article focused on ICD-10-CM conventions. We will discuss general coding guidelines for ICD-10-CM in part two, which we will be published in the January 5 issue of JustCoding News: Inpatient. Joel Moorhead MD, PhD, is an adjunct assistant professor at the Rollins School of Public Health at Emory University in Atlanta. He is also associate medical director for FairCode Associates in Baltimore. E-mail him at jmoorhe@sph.emory.edu.

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