Understanding ICD-10
The
conventions for the ICD-10-CM are the general rules for use of the
classification independent of the guidelines. These conventions are
incorporated within the Alphabetic Index and Tabular List of the ICD-10-CM as
instructional notes.
1.
The Alphabetic Index and Tabular List
The
ICD-10-CM is divided into the Alphabetic Index, an alphabetical list of terms
and their corresponding code, and the Tabular List, a structured list of codes
divided into chapters based on body system or condition. The Alphabetic Index
consists of the following parts: the Index of Diseases and Injury, the Index of
External Causes of Injury, the Table of Neoplasms and the Table of Drugs and
Chemicals.
2.
Format and Structure:
The
ICD-10-CM Tabular List contains categories, subcategories and codes. Characters
for categories, subcategories and codes may be either a letter or a number. All
categories are 3 characters. A three-character category that has no further
subdivision is equivalent to a code. Subcategories are either 4 or 5
characters. Codes may be 3, 4, 5, 6 or 7 characters. That is, each level of
subdivision after a category is a subcategory. The final level of subdivision
is a code. Codes that have applicable 7th characters are still referred to as
codes, not subcategories. A code that has an applicable 7th character is
considered invalid without the 7th character.
The
ICD-10-CM uses an indented format for ease in reference.
3.
Use of codes for reporting purposes
For
reporting purposes only codes are permissible, not categories or subcategories,
and any applicable 7th character is required.
4.
Placeholder character
The ICD-10-CM utilizes a placeholder character “X”. The “X” is
used as a placeholder at certain codes to allow for future expansion. An
example of this is at the poisoning, adverse effect and under dosing codes,
categories T36-T50.
Where
a placeholder exists, the X must be used in order for the code to be considered
a valid code.
5. 7th Characters
Certain
ICD-10-CM categories have applicable 7th characters. The applicable 7th character
is required for all codes within the category, or as the notes in the Tabular
List instruct. The 7th character must always be the 7th character in the data
field. If a code that requires a 7th character is not 6 characters, a
placeholder X must be used to fill in the empty characters.
6.
Abbreviations
a.
Alphabetic Index abbreviations
NEC
“Not elsewhere classifiable”
This
abbreviation in the Alphabetic Index represents “other specified”. When a
specific code is not available for a condition, the Alphabetic Index directs
the coder to the “other specified” code in the Tabular List.
NOS
“Not otherwise specified”
This
abbreviation is the equivalent of unspecified.
b.
Tabular List abbreviations
NEC
“Not elsewhere classifiable”
This
abbreviation in the Tabular List represents “other specified”. When a specific
code is not available for a condition the Tabular List includes an NEC entry
under a code to identify the code as the “other specified” code.
NOS
“Not otherwise specified”
This
abbreviation is the equivalent of unspecified.
7.
Punctuation
[
] Brackets are used in the Tabular List to enclose synonyms, alternative
wording or explanatory phrases. Brackets are used in the Alphabetic Index to
identify manifestation codes.
(
) Parentheses are used in both the Alphabetic Index and Tabular List to enclose
supplementary words that may be present or absent in the statement of a disease
or procedure without affecting the code number to which it is assigned. The
terms within the parentheses are referred to as nonessential modifiers. The
nonessential modifiers in the Alphabetic Index to Diseases apply to sub terms
following a main term except when a nonessential modifier and a subentry are
mutually exclusive, the subentry takes precedence. For example, in the
ICD-10-CM
Alphabetic
Index under the main term Enteritis, “acute” is a nonessential modifier and
“chronic” is a subentry. In this case, the nonessential modifier “acute” does
not apply to the subentry “chronic”.
:
Colons are used in the Tabular List after an incomplete term which needs one or
more of the modifiers following the colon to make it assignable to a given
category.
8. Use of “and”.
Specific Use refer to ICD-10 See Section I.A.14. Use of the term "And"
9. Other and Unspecified codes
a. “Other” codes
Codes titled “other” or “other specified” are for use when the information in the medical record provides detail for which a specific code does not exist. Alphabetic Index entries with NEC in the line designate “other” codes in the Tabular List. These Alphabetic Index entries represent specific disease entities for which no specific code exists so the term is included within an “other” code.
b. “Unspecified” codes
Codes titled “unspecified” are for use when the information in the medical record is insufficient to assign a more specific code. For those categories for which an unspecified code is not provided, the “other specified” code may represent both other and unspecified.
10. Includes Notes
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
11. Inclusion terms
List of terms is included under some codes. These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of “other specified” codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code
12. Excludes Notes
The ICD-10-CM has two types of excludes notes. Each type of note has a different definition for use but they are all similar in that they indicate that codes excluded from each other are independent of each other.
a. Excludes1
A type 1 Excludes note is a pure excludes note. It means “NOT CODED HERE!” An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
b. Excludes2
A type 2 Excludes note represents “Not included here”. An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.
13. Etiology/manifestation convention (“code first”, “use additional code” and “in diseases classified elsewhere” notes)
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation.
Wherever such a combination exists, there is a “use additional code” note at the etiology code, and a “code first” note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
In most cases the manifestation codes will have in the code title, “in diseases classified elsewhere.” Codes with this title are a component of the etiology/ manifestation convention. The code title indicates that it is a manifestation code. “In diseases classified elsewhere” codes are never permitted to be used as first-listed or principal diagnosis codes. They must be used in conjunction with an underlying condition code and they must be listed following the underlying condition. See category F02, Dementia in other diseases classified elsewhere, for an example of this convention.
There are manifestation codes that do not have “in diseases classified elsewhere” in the title. For such codes, there is a “use additional code” note at the etiology code and a “code first” note at the manifestation code and the rules for sequencing apply.
In addition to the notes in the Tabular List, these conditions also have a specific Alphabetic Index entry structure. In the Alphabetic Index both conditions are listed together with the etiology code first followed by the manifestation codes in brackets. The code in brackets is always to be sequenced second.
An example of the etiology/manifestation convention is dementia in Parkinson’s disease. In the Alphabetic Index, code G20 is listed first, followed by code F02.80 or F02.81 in brackets. Code G20 represents the underlying etiology, Parkinson’s disease, and must be sequenced first, whereas codes F02.80 and F02.81 represent the manifestation of dementia in diseases classified elsewhere, with or without behavioral disturbance.
“Code first” and “Use additional code” notes are also used as sequencing rules in the classification for certain codes that are not part of an etiology/ manifestation combination.
14. “And”
The word “and” should be interpreted to mean either “and” or “or” when it appears in a title.
For example, cases of “tuberculosis of bones”, “tuberculosis of joints” and “tuberculosis of bones and joints” are classified to subcategory A18.0, Tuberculosis of bones and joints.
15. “With”
The word “with” should be interpreted to mean “associated with” or “due to” when it appears in a code title, the Alphabetic Index, or an instructional note in the Tabular List.
The word “with” in the Alphabetic Index is sequenced immediately following the main term, not in alphabetical order.
16. “See” and “See Also”
The “see” instruction following a main term in the Alphabetic Index indicates that another term should be referenced. It is necessary to go to the main term referenced with the “see” note to locate the correct code.
A “see also” instruction following a main term in the Alphabetic Index instructs that there is another main term that may also be referenced that may provide additional Alphabetic Index entries that may be useful. It is not necessary to follow the “see also” note when the original main term provides the necessary code.
17. “Code also note”
A “code also” note instructs that two codes may be required to fully describe a condition, but this note does not provide sequencing direction.
18. Default codes
A code listed next to a main term in the ICD-10-CM Alphabetic Index is referred to as a default code. The default code represents that condition that is most commonly associated with the main term, or is the unspecified code for the condition. If a condition is documented in a medical record (for example, appendicitis) without any additional information, such as acute or chronic, the default code should be assigned.
B. General Coding Guidelines
1. Locating a code in the ICD-10-CM
To select a code in the classification that corresponds to a diagnosis or reason for visit documented in a medical record, first locate the term in the Alphabetic Index, and then verify the code in the Tabular List. Read and be guided by instructional notations that appear in both the Alphabetic Index and the Tabular List.
It is essential to use both the Alphabetic Index and Tabular List when locating and assigning a code. The Alphabetic Index does not always provide the full code. Selection of the full code, including laterality and any applicable 7th character can only be done in the Tabular List. A dash (-) at the end of an Alphabetic Index entry indicates that additional characters are required. Even if a dash is not included at the Alphabetic Index entry, it is necessary to refer to the Tabular List to verify that no 7th character is required.
2. Level of Detail in Coding
Diagnosis codes are to be used and reported at their highest number of characters available.
ICD-10-CM diagnosis codes are composed of codes with 3, 4, 5, 6 or 7 characters. Codes with three characters are included in ICD-10-CM as the heading of a category of codes that may be further subdivided by the use of fourth and/or fifth characters and/or sixth characters, which provide greater detail.
A three-character code is to be used only if it is not further subdivided. A code is invalid if it has not been coded to the full number of characters required for that code, including the 7th character, if applicable.
3. Code or codes from A00.0 through T88.9, Z00-Z99.8
The appropriate code or codes from A00.0 through T88.9, Z00-Z99.8 must be used to identify diagnoses, symptoms, conditions, problems, complaints or other reason(s) for the encounter/visit.
4. Signs and symptoms
Codes that describe symptoms and signs, as opposed to diagnoses, are acceptable for reporting purposes when a related definitive diagnosis has not been established (confirmed) by the provider. Chapter 18 of ICD-10-CM, Symptoms, Signs, and Abnormal Clinical and Laboratory Findings, Not Elsewhere Classified (codes R00.0 - R99) contains many, but not all codes for symptoms.
5. Conditions that are an integral part of a disease process
Signs and symptoms that are associated routinely with a disease process should not be assigned as additional codes, unless otherwise instructed by the classification.
6. Conditions that are not an integral part of a disease process
Additional signs and symptoms that may not be associated routinely with a disease process should be coded when present.
7. Multiple coding for a single condition
In addition to the etiology/manifestation convention that requires two codes to fully describe a single condition that affects multiple body systems, there are other single conditions that also require more than one code. “Use additional code” notes are found in the Tabular List at codes that are not part of an etiology/manifestation pair where a secondary code is useful to fully describe a condition. The sequencing rule is the same as the etiology/manifestation pair, “use additional code” indicates that a secondary code should be added.
For example, for bacterial infections that are not included in chapter 1, a secondary code from category B95, Streptococcus, Staphylococcus, and Enterococcus, as the cause of diseases classified elsewhere, or B96, Other bacterial agents as the cause of diseases classified elsewhere, may be required to identify the bacterial organism causing the infection. A “use additional code” note will normally be found at the infectious disease code, indicating a need for the organism code to be added as a secondary code.
“Code first” notes are also under certain codes that are not specifically manifestation codes but may be due to an underlying cause. When there is a “code first” note and an underlying condition is present, the underlying condition should be sequenced first.
“Code, if applicable, any causal condition first”, notes indicate that this code may be assigned as a principal diagnosis when the causal condition is unknown or not applicable. If a causal condition is known, then the code for that condition should be sequenced as the principal or first-listed diagnosis.
Multiple codes may be needed for sequela, complication codes and obstetric codes to more fully describe a condition. See the specific guidelines for these conditions for further instruction.
8. Acute and Chronic Conditions
If the same condition is described as both acute (sub-acute) and chronic, and separate subentries exist in the Alphabetic Index at the same indentation level, code both and sequence the acute (sub acute) code first.
9. Combination Code
A combination code is a single code used to classify:
Two diagnoses, or
A diagnosis with an associated secondary process (manifestation)
A diagnosis with an associated complication
Combination codes are identified by referring to subterm entries in the Alphabetic Index and by reading the inclusion and exclusion notes in the Tabular List.
Assign only the combination code when that code fully identifies the diagnostic conditions involved or when the Alphabetic Index so directs. Multiple coding should not be used when the classification provides a combination code that clearly identifies all of the elements documented in the diagnosis. When the combination code lacks necessary specificity in describing the manifestation or complication, an additional code should be used as a secondary code.
10. Sequela (Late Effects)
A sequela is the residual effect (condition produced) after the acute phase of an illness or injury has terminated. There is no time limit on when a sequela code can be used. The residual may be apparent early, such as in cerebral infarction, or it may occur months or years later, such as that due to a previous injury. Coding of sequela generally requires two codes sequenced in the following order: The condition or nature of the sequela is sequenced first. The sequela code is sequenced second.
An exception to the above guidelines are those instances where the code for the sequela is followed by a manifestation code identified in the Tabular List and title, or the sequela code has been expanded (at the fourth, fifth or sixth character levels) to include the manifestation(s). The code for the acute phase ICD of an illness or injury that led to the sequela is never used with a code for the late effect.
Code any condition described at the time of discharge as “impending” or “threatened” as follows:
If it did occur, code as confirmed diagnosis.
If it did not occur, reference the Alphabetic Index to determine if the condition has a subentry term for “impending” or “threatened” and also reference main term entries for “Impending” and for “Threatened.”
If the subterms are listed, assign the given code.
If the subterms are not listed, code the existing underlying condition(s) and not the condition described as impending or threatened.
12. Reporting Same Diagnosis Code More than Once
Each unique ICD-10-CM diagnosis code may be reported only once for an encounter. This applies to bilateral conditions when there are no distinct codes identifying laterality or two different conditions classified to the same ICD-10-CM diagnosis code.
13. Laterality
Some ICD-10-CM codes indicate laterality, specifying whether the condition occurs on the left, right or is bilateral. If no bilateral code is provided and the condition is bilateral, assign separate codes for both the left and right side. If the side is not identified in the medical record, assign the code for the unspecified side.
14. Documentation for BMI, Non-pressure ulcers and Pressure Ulcer Stages
For the Body Mass Index (BMI), depth of non-pressure chronic ulcers and pressure ulcer stage codes, code assignment may be based on medical record documentation from clinicians who are not the patient’s provider (i.e., physician or other qualified healthcare practitioner legally accountable for establishing the patient’s diagnosis), since this information is typically documented by other clinicians involved in the care of the patient (e.g., a dietitian often documents the BMI and nurses often documents the pressure ulcer stages). However, the associated diagnosis (such as overweight, obesity, or pressure ulcer) must be documented by the patient’s provider. If there is conflicting medical record documentation, either from the same clinician or different clinicians, the patient’s attending provider should be queried for clarification.
The BMI codes should only be reported as secondary diagnoses. As with all other secondary diagnosis codes, the BMI codes should only be assigned when they meet the definition of a reportable additional diagnosis
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