Start preparing for ICD-10-CM by comparing differences in common diagnosis codes

by Kathy DeVault, RHIA, CCS, CCS-P

Although some aspects of ICD-10-CM are similar to ICD-9-CM, coders will need to learn and understand some new aspects of ICD-10-CM.

As far as similarities go, ICD-10-CM has the same hierarchical structure as ICD-9-CM, and all codes with the same first three characters have common traits. In ICD-10-CM, up to four characters may follow the decimal; however, not every code will have four characters after the decimal.

ICD-10-CM also has the same use of notes and instructions as ICD-9-CM. When a note appears under a three-character code, it applies to all codes within the category, and notes under a specific code apply to the single code. ICD-10-CM and ICD-9-CM also share many of the same conventions and guidelines.

One of the biggest differences in ICD-10-CM is the greater specificity and clinical detail found in the codes. The Centers for Disease Control (CDC) updated the medical terminology and classification of diseases to be consistent with current clinical practice. Let’s look at some of the diagnoses and chapters in ICD-10-CM that differ significantly from ICD-9-CM.

Diabetes mellitus
First, in Chapter 4: Endocrine, Nutritional, and Metabolic Diseases (E00-E90), is diabetes mellitus. In ICD-10-CM, the diabetes mellitus codes are combination codes that include the:

  • Type of diabetes
  • Body system affected
  • Complications affecting that body system

These combination codes make coding diabetes mellitus less confusing and decreases the number of codes necessary to describe diabetic complications. Diabetes may be coded with as many combination codes as necessary to fully describe all complications. They should be sequenced based on the reason for a particular encounter.

In ICD-10-CM, the diabetes mellitus codes are no longer classified as controlled or uncontrolled. If provider documentation includes words such as uncontrolled, out of control, or poorly controlled, the classification directs the coder to code the type of diabetes with hyperglycemia.

The five categories of diabetes mellitus are:

  • E08 – Diabetes mellitus due to underlying condition
  • E09 – Drug or chemical induced diabetes mellitus
  • E10 – Type 1 diabetes mellitus
  • E11 – Type 2 diabetes mellitus
  • E13 – Other specified diabetes mellitus

Category O24 is used to identify diabetes mellitus in pregnancy, childbirth, or the puerperium.

ICD-10-CM diabetes mellitus code examples:

  • E09.01 – Drug or chemical induced diabetes mellitus with hyperosmolarity with coma
  • E10.11 – Type 1 diabetes mellitus with ketoacidosis with coma
  • E11.40 – Type 2 diabetes mellitus with diabetic nephropathy, unspecified
  • E13.621 – Other specified diabetes mellitus with foot ulcer

Chapter 10 in ICD-10-CM, Diseases of the Respiratory System (J00-J99), includes the diagnosis of asthma. The CDC updated the terminology used to describe asthma in ICD-10-CM to reflect the current clinical classification of asthma. Instead of asthma being described as extrinsic or intrinsic, it is classified as mild intermittent, mild persistent, moderate persistent, and severe persistent.

Asthma is classified to category J45 with the fourth character classifying the type of asthma and the fifth character classifying the asthma as with status asthmaticus (2) or with acute exacerbation (1). This diagnosis will require specific documentation and additional provider education for the most appropriate code assignment in ICD-10-CM.

Category J45 includes several use additional code notes to identify the following:

  • Exposure to environmental tobacco smoke (Z77.22)
  • Exposure to tobacco smoke in the perinatal period (P96.81)
  • History of tobacco use (Z87.891)
  • Occupational exposure to environmental tobacco smoke (Z57.31)
  • Tobacco dependence (F17.-)
  • Tobacco use (Z72.0)

Another chapter that has different classification is Chapter 15: Pregnancy, Childbirth and the Puerperium (O00-O9A). In ICD-9-CM obstetrics codes requires a fifth digit to identify the episode of care (delivered, antepartum, or post-partum). The codes in Chapter 15 of ICD-10-CM identify the trimester in which the condition occurred rather than the episode of care. Some codes in this chapter require a numeric seventh character extension.

Because certain obstetric conditions or complications occur during certain trimesters, not all conditions include codes for all three trimesters. The note at the beginning of the chapter defines the trimesters. Trimesters are counted from the first day of the last menstrual period and are defined as follows:

  • First trimester – less than 14 weeks 0 days
  • Second trimester – 14 weeks 0 days to less than 28 weeks 0 days
  • Third trimester – 28 weeks 0 days until delivery

Physician documentation is required to correctly assign trimester. Documentation of “weeks of gestation” can be used to convert to the correct trimester.

Certain codes in chapter 15 require a seventh character extension to identify the fetus in a multiple gestation that is affected by the condition being coded. The applicable seventh character extensions are:

  • 0 – not applicable or unspecified
  • 1 – fetus 1
  • 2 – fetus 2
  • 3 – fetus 3
  • 4 – fetus 4
  • 5 – fetus 5
  • 9 – other fetus

The seventh character ‘0’ is for single gestations and multiple gestations where the affected fetus is unspecified. Seventh characters 1 through 9 are for cases of multiple gestations to identify the fetus for which the code applies. A code from category O30 (Multiple gestation) must also be assigned when assigning these codes.

Finally, Chapter 19: Injury, Poisoning, and Certain Other Consequences of External Causes (S00-T88) in ICD-10-CM differs significantly from ICD-9-CM. In ICD-10-CM, injuries are grouped by body part rather than by categories of injury, so that all injuries of the specific site (such as head and neck) are grouped together rather than groupings of all fractures or all open wounds.

Chapter 19 encompasses two alpha characters in ICD-10-CM. The S section provides codes for the various types of injuries related to single body regions. The T section covers injuries to unspecified body regions as well as poisonings and certain other consequences of external causes.

Many codes, such as fractures, include much greater specificity in ICD-10-CM. Some of the information that may be found in fracture codes includes the type of fracture, specific anatomical site, whether the fracture is displaced or not, laterality, routine versus delayed healing, nonunions, and malunions. Laterality and identification of type of encounter (initial, subsequent, sequel) are a significant component of the code expansion.

The fracture seventh character extensions include:

  • A – Initial encounter for closed fracture
  • B – Initial encounter for open fracture
  • D – Subsequent encounter for fracture with routine healing
  • G – Subsequent encounter for fracture with delayed healing
  • K – Subsequent encounter for fracture with nonunion
  • P – Subsequent encounter for fracture with malunions
  • S – Sequela

Several fracture categories provide a seventh character extension to designate the specific type of open fracture. These designations are based on the Gustilo open fracture classification.

The extensions for “initial encounter” are used while the patient is receiving active treatment for the injury. Active treatment includes surgical treatment, emergency department encounter, and evaluation and treatment by a new physician.

The extensions for “subsequent encounter” are used for encounters after the patient has received active treatment and is receiving routine care during the healing or recovery phase. This includes:

  • Cast change or removal
  • Removal of external or internal fixation device
  • Medication adjustment
  • Other aftercare and follow-up visits following injury treatment

The aftercare Z codes should not be used for aftercare of injuries. For aftercare of an injury, the coder will assign the acute injury code with the appropriate seventh character for “subsequent encounter.”

ICD-10-CM includes combination codes for poisonings and the associated external cause (accidental, intentional self-harm, assault, and undetermined).

ICD-10-CM also introduces the new concept of underdosing. Underdosing is taking less of a medication than is prescribed by a physician or the manufacturer’s instruction, with a resulting negative health consequence.

This is just a small sampling of the differences between ICD-9-CM and ICD-10-CM. Additional review and education is necessary for coders to fully understand and apply the changes in ICD-10-CM.

Editor’s Note: Kathy DeVault is Professional Practice Manager for the American Health Information Management Association in Chicago. E-mail your questions to Senior Managing Editor Michelle A. Leppert, CPC-A, at

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