ICD-10-CM is not so foreign. Much of what we are familiar with as users of ICD-9-CM remains a part of ICD-10-CM. There are some clinical modifications made to ICD-10-CM's structure and conventions that should be understood in order to accurately use the system and assign a correct code from ICD-10-CM.

ICD-10-CM contains both a tabular list, volume 1, and an alphabetic index, volume 3, with their conventions. The alphabetic index in ICD-10-CM is divided into three sections, similar to ICD-9-CM. It consists of the main alphabetic index to disease and injury, an external cause index, and a table of drugs and chemicals.

Volume 1 of ICD-10-CM contains the tabular listing of alphanumeric codes. The same hierarchical organization of ICD-9 applies to ICD-10: All codes with the same first three digits have common traits. Each digit beyond three adds more specificity. In ICD-10-CM for use in the United States, valid codes can contain anywhere from three to seven characters.

All codes in ICD-10-CM are alphanumeric, i.e., one letter followed by two numbers at the three-character level, as opposed to three numeric characters in the main classification of ICD-9-CM. Of the 26 available letters, all but the letter U is used, which was reserved for additions and changes that may need to be incorporated in the future or for classification difficulties that may arise between revisions. Some three-character categories have been left vacant for future expansion and revision.

In ICD-10, a chapter may encompass more than one letter and more than one chapter may share a letter:

Chapter 2-Neoplasms (C00-D48)

Chapter 3-Diseases of the Blood and Blood-Forming Organs and Certain Disorders Involving the Immune System (D50-D89)

The tabular list comprises 22 chapters versus the 17 main chapters plus two supplementary classifications (V and E codes) in ICD-9-CM. The External Causes of Morbidity and Mortality and Factors Influencing Health Status" and "Contact with Health Services" chapters are no longer considered to be supplementary, but are a part of the core classification. E codes of ICD-9-CM become V codes, W codes, X codes, and Y codes in ICD-10-CM and ICD-9-CM's V codes become Z codes in ICD-10-CM:

V03.10a Pedestrian on foot injured in collision with car, pick-up truck or van in traffic accident, initial encounter

W52.q Crushed, pushed or stepped on by crowd or human stampede, sequelae

X37.0a Hurricane, initial encounter

Y65.2 Failure in suture or ligature during surgical operation

Z80.49 Family history of malignant neoplasm of other genital organs

The three new chapters in ICD-10 are "Diseases of the Eye and Adnexa," "Diseases of the Ear and Mastoid Process," and "Codes for Special Purposes."

New Features in ICD-10-CM
One major difference in ICD-10-CM is that codes will have complete descriptions rather than relying on the hierarchy. In ICD-9-CM, often the user must review the description of the category in order to determine the complete intent of the subcategory or subclassification. One needs to review the title of the category in order to understand the meaning of the code. In ICD-10-CM, the subcategory titles are usually complete, with the exception of some codes in the neoplasm and health circumstances sections. In ICD-10-CM, NCHS is striving to make all code descriptions complete.

Typically, in ICD-9-CM, codes are presented in this fashion:

451 Phlebitis and thrombophlebitis
         451.0 of superficial vessels of lower extremities

In ICD-10-CM, most codes have complete descriptions:

I80 Phlebitis and thrombophlebitis
I80.0 Phlebitis and thrombophlebitis of superficial vessels of lower extremities
I80.03 Phlebitis and thrombophlebitis of superficial vessels of lower extremities, bilateral

New categories for postprocedural disorders specific to a particular body system have been created at the end of each body system chapter. There has been no change to the classification of those situations in which postprocedural conditions are not specific to a particular body system, such as postoperative hemorrhage. These can be found in chapter 19, "Injury, Poisoning and Certain Other Consequences of External Causes," which is compatible to ICD-9-CM.

In ICD-9-CM, complications specific to the digestive system are not located under one category, but can be found in categories 564, 569, and 997. In ICD-10-CM, complications specific to the digestive system are all located under a new category for postprocedural disorders.

Axis of Classification
Diseases can be arranged in a variety of ways: according to etiology, anatomy, or severity. The particular criterion chosen is called the axis of classification. Anatomy is the primary axis of classification of ICD-10-CM. Thus, there are chapters entitled "Diseases of the Circulatory System" and "Diseases of the Genitourinary System." ICD-10-CM employs other axes as well, such as etiology, as in the chapter, "Certain Infectious and Parasitic Diseases."

Different axes are used in classifying different diseases within the same chapters. The choice is based upon the most important aspects of the disease from both a statistical and clinical point of view. For example:

Pneumonia: etiology or cause of the pneumonia
Malignant neoplasm: site
Cardiac arrhythmia: type
Leukemia: morphology

Structure of ICD-10-PCS
The developers of ICD-10-PCS resolved problems inherent in the existing procedural coding systems by rewriting the system's salient features. Codes in ICD-10-PCS contain seven alphanumeric characters, and although there are thousands of possible codes, PCS distills all medical services into about 30 procedures. There is no numeric listing of codes. Rather, there are 16 sections filled with tables that determine code selection. The code tables are designed so that each character has a specific meaning. Each code must include characters in each position. The first character identifies what type of procedure is being reported in specialty sections such as medical and surgical, obstetrics, imaging, radiation oncology, osteopathic, mental health, laboratory, etc. Nearly half of the specialty sections reflected in the first character of ICD-10-PCS remain undesignated and there is tremendous room for expansion into other arenas, like home health services or yet-undiscovered technologies.

Each subsequent place in the code has a specific function. The meaning of each place in a code may differ from one section to another. Thus, the fifth character in the imaging section (5) identifies the contrast material used, while the fifth character in the medical and surgical section (0) identifies the surgical approach. The second character identifies the body system in all sections except "Rehabilitation" and "Mental Health." In those sections, the second character identifies the type of procedure performed. The numbers and letters that fill the character positions for each section are identified in a key. The letter "z" is used to indicate that a character is not applicable.

The characters for the Medical and Surgical section are organized as follows:

In ICD-10-PCS tabular list, a separate table is created for each possible combination of the first three characters of a code. For each body system, the tabular list begins with a listing of the operations performed (i.e., the root operations).

This is the table that would be referenced to determine the correct code for transorifice intraluminal endoscopic fragmentation of calculus in the left renal pelvis:

0TF Rubric

The ICD-10-PCS code for this procedure would be built as follows:

0TF48ZZ Transorifice intraluminal endoscopic fragmentation of calculus of left renal pelvis

The index allows codes to be located alphabetically and is arranged by root operations with subentries by body system, body part, operation, and device. The index may also be consulted for a specific operation term such as hysterectomy, where a cross-reference advises the coder to see "Resection, Female Reproductive System, 0VT." This is an example of an idex entry: Fascioplasty - see Repair, Bursa, Ligaments, Fascia 0MG
Fine Needle Aspiration - see Excision
Fix - see Repair
Flushing - see Irrigation
Formation - see Creation
Fragmentation -
By Body System:

Anatomical Regions 0XF
Central Nervous System 00F
Eye 08F
Female Reproductive System 0VF
Gastrointestinal System 0DF
Heart & Great Vessels 02F
Hepatobiliary System & Pancreas 0FF
Mouth & Throat 0CF
Respiratory System 0BF
Urinary System 0TF

By Body Part:

Ampulla of Vater 0FFB
Anus 0DFQ
Appendix 0DFJ
Bladder 0TF8
Bladder Neck 0TF9
Bronchus
Lingula 0BF9
Lower Lobe 0BF
Main 0BF
Middle Lobe, Right 0BF5
Segmental, Lingula 0BF9
Upper Lobe 0BF