2.05: ICD-10-CM

ICD-10-CM is a vastly expanded set of diagnosis codes that’s set to replace ICD-9-CM in 2015. While these code sets share a number of similarities, ICD-10-CM is different in its format and organization. This course will teach you what ICD-10-CM is and will give you a foundation for using it in everyday coding.

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2.05: ICD-10-CM

The Changeover from ICD-9-CM to ICD-10-CM

In the United States, we’ve been using the ICD-9-CM code set since the late 1970s. ICD codes are updated every 10 to 15 years, and typically just include expansions to existing code sets. The upgrade from ICD-9 to ICD-10, however, involved a shift in format and organization. Because of this shift in format, and the headaches that go along with reformatting every aspect of medical reporting in the industry, the United States was unwilling to upgrade to ICD-10 when it was initially published in 1999. In the years since, the deadline to upgrade to ICD-10 in the US has been pushed back repeatedly.

As a result of this, the United States’ primary code set for representing diagnoses is more than 10 years out of date with the rest of the world. Canada and Australia, for instance, updated to some form of ICD-10 in the early 2000s. The U.S. had originally intended to upgrade to ICD-10 (and its attached Clinical Modification, ICD-10-CM) in October of 2013, then delayed it to 2014, and now has delayed it for another year to October 1, 2015. This is considered the “hard” deadline for the upgrade, and coders around the country are hard at work learning the ins and outs of this new, significantly larger code set.

This presents a bit of a challenge for incoming medical coders. The ICD-9-CM set is still in use today, and coders must be able to use it quickly and efficiently. But, the ICD-10-CM upgrade is looming, and coders must also be able to use that code set effectively. Adding to the complications is the fact that for two years after the upgrade, ICD-9-CM codes will still be used in a sort of transitional phase, meaning coders must be able to move between code sets freely.

With that challenge laid out, let’s take a look at ICD-10-CM and discover more about this new and important element of health informatics.

The Code Itself

As we mentioned, ICD-10-CM code is similar to ICD-9-CM in what it does, but distinct in it’s format and layout. Where ICD-9-CM is five digits and almost entirely numeric, ICD-10-CM is seven characters and entirely alphanumeric.

This is a problem for a number of reasons. For one, the US is no longer “speaking the same language” as the other countries in the world. One of the benefits of the ICD code system is its universality. While each country that adopts ICD codes tends to tweak it in certain ways (like the United States’ Clinical Modification), the roots of the codes are still the same. Not so in the US. Since we’re still using a five-character, numeric code set, and the rest of the world is using a seven-character, alphanumeric system, it’s hard to track

The more pressing need comes from the format of ICD-9-CM itself. To put it simply, ICD-9-CM is out of room. As the field of medicine has grown by leaps and bounds in the years since ICD-9-CM was implemented, the code set has struggled to keep up. There are now too many new diseases, diagnoses, procedures for the code set to keep up.

If we remember our mission of always “coding to the highest level of specificity,” you can see that this is a real problem. As medical practice has developed and diversified, the old ICD-9-CM code set is increasingly incapable of providing the exact right codes. While ICD-9-CM has developed a workaround in the form of “Not Elsewhere Classified” codes and other unlisted codes, it’s not ideal to work with intentionally nonspecific codes.

Enter ICD-10-CM. The code set is significantly larger than ICD-9-CM (there are 13,000 ICD-9 codes and 68,000 ICD-10 codes), and its increased number of subcategories and subclassifications (the digits after the decimal point), allow for a far greater level of specificity in coding. ICD-10-CM is also more flexible, and was designed in such a way that eases the entrance of codes for new, recently discovered, or expanded diagnoses.

Layout and Organization

ICD-10-CM is, as we’ve mentioned, a seven-character, alphanumeric code. Each code begins with a letter. That letter is followed by two numbers. Like ICD-9-CM, the first three characters of ICD-10-CM are the “category.” The category describes the general type of the injury or disease. The category is followed by a decimal point and the subcategory. This is followed by up to two subclassifications, which further explain the cause, manifestation, location, severity, and type of injury or disease. The last character is the extension.

The extension describes the type of encounter this is. That is, if this is the first time a healthcare provider has seen the patient for this condition/injury/disease, it’s listed as the “initial encounter.” Every encounter after the first is listed as a “subsequent encounter.” Patient visits related to the effects of a previous injury or disease are listed with the term “sequela.”

To review: the first digit of an ICD-10-CM code is always an alpha, the second digit is always numeric, and digits three through seven may be alpha or numeric. Here’s a simplified look at ICD-10-CM’s format.

A01 – {Disease}

  • A01.0 {Disease] of the lungs
    • A01.01 … simple
    • A01.02 … complex
      • A01.020 … affecting the trachea
      • A01.021 … affecting the cardiopulmonary system
        • A01.021A … initial encounter
        • A01.021D … subsequent encounter
        • A01.021S … sequela

As you can see from the example, ICD-10-CM branches much farther out than ICD-9-CM. ICD-10-CM allows us to code the location and manifestation of a disease or injury far more accurately, and the extensions reduce the administrative burden by documenting both the diagnosis and whether this injury or illness has been examined before.

Still, ICD-10-CM and ICD-9-CM share more similarities than you might think. Like ICD-9-CM, the ICD-10-CM code manual is divided into three volumes. Volume I is the tabular index, much like that of ICD-9-CM. Volume II is, again, the alphabetic index. Volume III lists procedure codes that are only used by hospitals. (We won’t be covering ICD-10-CM Volume III codes in these courses).

Like the first volume of ICD-9-CM, ICD-10-CM is divided into ranges based on the type of injury or disease they document. ICD-10-CM’s division closely follows ICD-9-CM’s separation into “chapters.” For a breakdown of the ICD-10-CM code manual download our ebook.

Range Topic
A00-B99 Certain infections and parasitic diseases
C00-D49 Neoplasms
D50-D89 Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism
E00-E89 Endocrine, nutritional and metabolic diseases
F01-F99 Mental, Behavioral and Neurodevelopmental disorders
G00-G99 Diseases of the nervous system
H00-H59 Diseases of the eye and adnexa
H60-H95 Diseases of the ear and mastoid process
I00-I99 Diseases of the circulatory system
J00-J99 Diseases of the respiratory system
K00-K95 Diseases of the digestive system
L00-L99 Diseases of the skin and subcutaneous tissue
M00-M99 Diseases of the musculoskeletal system and connective tissue
N00-N99 Diseases of the genitourinary system
O00- O9A Pregnancy, childbirth, and puerperium
P00-P96 Certain conditions originating in the perinatal period
Q00-Q99 Congenital malformations, deformations and chromosomal abnormalities
R00-R99 Symptoms, signs, and abnormal clinical laboratory findings, not elsewhere classified
S00-T88 Injury, poisoning, and certain other consequences of external causes
V00-Y99 External causes of morbidity
Z00-Z99 Factors influencing health status and contact with health services

What’s different, as you may imagine, is the levels of detail to which all of these codes can go.

Let’s consider a side-by-side example.

Injury: Closed fracture of the distal phalanx of right index finger Injury: Closed fracture of distal phalanx of right index finger
Chapter 17 – Injury and Poisoning810-819 Fracture of Upper limb

  • 816 Fracture of one or more phalanxes of hand
    • 816.0 – closed fracture of one or more phalanges of the hand
      • 816.00 – closed fracture of phalanx or phalanges of the hand, unspecified
      • 816.01 – closed fracture of middle or proximal phalanx or phalanges of hand
      • 816.02 – closed fracture of distal phalanx or phalanges of hand
S00-T88 – Injury, poisoning and certain other consequences of external causesS60-S69 – Injuries to the wrist, hand and fingers

  • S62 – Fracture at wrist and hand level
    • S62.0 – fracture at navicular [scaphoid] bone of wrist
    • S62.5 – fracture of thumb
    • S62.6 – fracture of other and unspecified finger(s)
      • S62.60 – fracture of unspecified phalanx of finger
      • S62.61 – displaced fracture of proximal phalanx of finger
      • S62.63 – displaced fracture of distal phalanx of finger
        • S62.630 – Displaced fracture of distal phalanx of right index finger
          • S62.630A – … initial encounter for closed fracture
          • S62.630B – … initial encounter for open fracture
          • S62.630D – … initial encounter for fracture with routine healing
          • Etc.

As you can clearly see, ICD-10-CM allows coders to code to a much higher level of specificity. ICD-10-CM introduces laterality—which side the injury or infection is on—and substantially increases the amount of information about the diagnosis. Instead of leaving off at “closed fracture of distal phalanx of hand,” as we would in ICD-9-CM, we can go into fine detail about what type of fracture, on which finger, on which hand—even which visit this is the for the particular injury.


Aside from its format and organization, ICD-10-CM is very similar to ICD-9-CM. It includes all of the conventions you’d find in ICD-9-CM, including:

  • Brackets [ ]
  • Parentheses ( )
  • “Includes”
  • “Excludes”
    • There is a slight variation here: ICD-10-CM includes two types of “Excludes” conventions
      • Excludes1: lists codes that should never be coded with the code listed above. You can think of this as a “hard excludes.”
      • Excludes2: lists other codes for conditions/injuries that may be a part of the condition, but are not included here. This is more of a “soft excludes.” An Excludes2 note functions similarly to a “See Also” note
  • “Code first”
  • “Use Additional Code”
  • “In Disease Elsewhere Classified”
  • “See”
  • “See Also”
  • “Not Elsewhere Classified”
  • “Not Otherwise Specified”

ICD-10-CM has another important convention that has to do with the code’s extensions. Remember, extensions typically provide information what encounter this is for the healthcare provider with the patient. These are not always included, but in the case that they are, they cannot simply be appended to the end of whatever code is attached. Extensions are only found in the seventh character of an ICD-10-CM code.

If a coder has to include an extension for an initial encounter on a code that does not have six characters, they must add placeholder characters. Coders use an ‘X’ for the placeholder digit.

If, for example, a coder needs to code an instance of poisoning by unintentional underdosing of antibiotic penicillin, the coder would use T36.0X1A. In this case, the fifth digit is empty, and so we’d use the placeholder character ‘X.’ Remember that placeholder characters are only used when an extension is necessary. Most ICD-10-CM codes do not include an extension for the encounter.

Now that we’ve got a better idea of what ICD-10-CM looks like and how it’s organized, it’s time to take a brief look at how to use this code. We’ll cover that in our next course, and we’ll talk about transferring codes from ICD-9-CM to ICD-10-CM, or ‘crosswalking.’

Video: ICD-10-CM

ICD-10-CM is a vastly expanded set of diagnosis codes that’s set to replace ICD-9-CM in 2015. While these code sets share a number of similarities, ICD-10-CM is different in its format and organization. This video will teach you what ICD-10-CM is and will give you a foundation for using it in everyday coding.