What is ICD-10?

ICD-10 refers to the tenth edition of the International Classification of Diseases, which is a medical coding system chiefly designed by the World Health Organization (WHO) to catalog health conditions by categories of similar diseases under which more specific conditions are listed, thus mapping nuanced diseases to broader morbidities.

Many countries now use national variations of ICD-10, each modified to align with their unique healthcare infrastructure.

The US version of ICD-10, created by the Centers for Medicare & Medicaid Services (CMS) and the National Center for Health Statistics (NCHS), consists of two medical code sets—ICD-10-CM and ICD-10-PCS.

ICD-10-PCS stands for the International Classification of Diseases, Tenth Revision, Procedure Coding System. As indicated by its name, ICD-10-PCS is a procedural classification system of medical codes. It is used in hospital settings to report inpatient procedures.

ICD-10-CM stands for the International Classification of Diseases, Tenth Revision, Clinical Modification. Used for medical claim reporting in all healthcare settings, ICD-10-CM is a standardized classification system of diagnosis codes that represent conditions and diseases, related health problems, abnormal findings, signs and symptoms, injuries, external causes of injuries and diseases, and social circumstances.

For a medical provider to receive reimbursement for medical services, ICD-10-CM codes are required to be submitted to the payer. While CPT® codes depict the services provided to the patient, ICD-10-CM codes depict the patient’s diagnoses that justify the services rendered as medically necessary.

The Origins of ICD-10 Coding

The roots of ICD-10 coding go back to the 1850s. The first edition, known as the International List of Causes of Death, was adopted by the International Statistical Institute in 1893.

WHO assumed oversight of the International Classification of Diseases (ICD) in 1948 with the main intention of tracking—and helping to eliminate—diseases within various populations. At the time, the Sixth Revision, which introduced causes of morbidity to the system, had just been published.

In 1957 and 1968, WHO released ICD-7 and ICD-8, respectively. Shortly after the release of ICD-9 in 1979, the US created its own version, known as the International Classification of Diseases, Ninth Revision, Clinical Modification—or, ICD-9-CM.

The development of ICD-9-CM was a tremendous boon. Not only did the new system expand the ability to capture enhanced morbidity data, but it also incorporated surgical procedures and other items necessary to categorize the needs of hospitals.

But ICD-9-CM, updated annually by CMS and the NCHS, was a limited system with a limited capacity for the addition of codes to keep pace with modern healthcare. And it was already a three-volume set, with the first two volumes dedicated to diagnosis codes and the third volume containing inpatient procedural codes.

So, after decades in the making, CMS and NCHS adopted ICD-10 and adapted the classification to create a new version, the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM), which no longer included the third volume of inpatient procedure codes.

What happened to the inpatient procedure codes? CMS determined the need for better organization and funded a project with 3M Health Information Systems in 1995 to develop the International Classification of Diseases, Tenth Revision, Procedure Coding System (ICD-10-PCS).

The Difference Between ICD-10-CM & ICD-10-PCS

Both ICD-10-CM and ICD-10-PCS came into effect for medical claims reporting on Oct.1, 2015. But the two code sets differ vastly. The primary distinctions are:

• ICD-10-CM—diagnosis code set used for all healthcare settings
• ICD-10-PCS—procedure code set used only in hospital inpatient settings

The terms ICD-10-CM and ICD-10 are used interchangeably in the US. This linguistic trend underscores the distinction between CM and PCS, in that ICD-10-CM is ubiquitous across healthcare settings, used by every medical coder as the singular means to report diagnoses.

The PCS code set, on the other hand, is one of two procedural coding systems. But unlike CPT^®, ICD-10-PCS is used strictly in hospital inpatient healthcare settings.

ICD-10 Provides Greater Specificity

Though some circumstance still require ICD-9 to ICD-10 code conversion, those circumstances are becoming uncommon, and ICD-9 is gradually fading into coding history.

The ICD-10 codes we use today are more specific than ICD-9-CM codes and allow for detailed classifications of patients’ conditions, injuries, and diseases. Medical coders are now equipped to capture anatomic sites, etiologies, comorbidities and complications, as well as severity of illnesses.  

The magnitude of ICD-10 codes currently in effect—72,184 versus 13,000 diagnosis codes in ICD-9-CM—illustrates the increased granularity available to represent real-world clinical practice and medical technology advances.

And that’s to say nothing of the enhanced capacity to provide essential data of disease patterns and outbreaks of disease, and to help illuminate characteristics and circumstances of individuals so affected.

With greater specificity, providers and payers can use ICD-10 diagnosis codes to track information about patients’ conditions and the types and number of treatments patients receive. They can gather and analyze code utilization to:

• Measure the safety and efficacy of patient care
• Determine the health status and risk factors of defined populations
• Improve and monitor providers’ performances
• Assess healthcare costs
• Investigate and prevent coding and billing abuses

Structure of ICD-10 Codes

ICD-10-CM codes consist of three to seven characters. Every code begins with an alpha character, which is indicative of the chapter to which the code is classified. The second and third characters are numbers. The fourth, fifth, sixth, and seventh characters can be numbers or letters.

Here are some examples of ICD-10 codes and the conditions they represent.

• G10 (Huntington's disease)
• K26.1 (Acute duodenal ulcer with perforation)
• A37.81 (Whooping cough due to other Bordetella species with pneumonia)
• I25.111 (Atherosclerotic heart disease of native coronary artery with angina pectoris with documented spasm)
• M80.021G (Age-related osteoporosis with current pathological fracture, right humerus; subsequent encounter for fracture with delayed healing)

Notice that with each additional character, the ICD-10 code depicts greater diagnostic information. You must always code diagnoses to the highest level of specificity available in the ICD-10 code set.

For instance, you should not code N04 for a patient diagnosed with nephrotic syndrome with minor glomerular abnormality. The finding of minor glomerular abnormality calls for an additional digit and would be coded as N04.0.

This degree of coding detail, of course, is not something you need to memorize. The ICD-10 list of codes is organized to lead you to the most specific diagnosis code selection.

Navigating ICD-10 Codes

ICD-10-CM includes an official Index, official Conventions, and official Guidelines. These are designed to help medical coders find and assign the correct diagnosis codes for their patients’ conditions.

Instructions and Conventions

The ICD-10 code set includes Section I Conventions, general coding guidelines applicable to the overall classification, and chapter-specific guidelines. Sections II – IV Conventions outline rules and principles for the selection of primary diagnoses, reporting additional diagnoses, and diagnostic coding and reporting of outpatient services.

Additionally, the Official Guidelines for Coding and Reporting, based on sequencing instructions in the Tabular List and Alphabetic Index of ICD-10-CM, provide further assistance for correct ICD-10 coding.

Alphabetic Index

This four-part index encompasses the Index of Diseases and Injury, the Index of External Causes of Injury, the Table of Neoplasms, and the Table of Drugs and Chemicals, all of which are designed to streamline the process of locating the necessary diagnosis codes and ICD-10 coding instructions.  

Index to Diseases and Injuries

Arranged alphabetically across hundreds of pages, this index list diseases, injuries, and diagnostic terms, along with their associated codes (or code categories). Sub-lists of related or more-detailed terms with their corresponding codes appear beneath many of the main terms.

Table of Neoplasms

This table enables you to locate codes for neoplasms by anatomical site and then quickly narrow your selection by cross-referencing the anatomical location with six traits, depending on whether the diagnosis is malignant primary, malignant secondary, Ca in situ, benign, of uncertain behavior, or of unspecified behavior.

(The neoplasm diagnosis codes are laid out in table format to condense the index, which would consume reams of pages if laid out in list format.)

Table of Drugs and Chemicals

Similar to the Table of Neoplasms, the Table of Drugs and Chemicals allows you to locate codes for poisoning or allergic reactions by cross-referencing the responsible substance with six circumstances that specify whether the substance-related condition was accidental, intentional self-harm, assault, undetermined, adverse effect, or the result of underdosing.

Index of External Causes of Injury

ICD-10 external cause codes provide details explaining the events surrounding an injury, which are especially useful in collecting statistics for policy decisions concerning public health. These ICD-10 codes also play an important role in workers’ compensation claims.

The Index of External Causes of Injury is arranged similar to the Index to Diseases and Injuries, listing entries and sub-entries in alphabetical order along with their corresponding codes.

Tabular List

The Tabular List refers to the actual listing of ICD-10 codes and their descriptors. You’ll also find instructions that will help you apply the codes correctly, as well as lists of additional diagnoses that a code applies to, sequencing rules, or which diagnoses codes are excluded from an ICD-10 code.

The Tabular List is organized into 21 chapters according to body system or condition, with diagnosis codes listed alphanumerically in each chapter.

ICD-10-CM Chapters and Code Ranges

Using the ICD-10 Tabular List

Remember—an ICD-10 code always begins with a letter and is followed by 2 numbers. The first 3 characters refer to the code category. As such, they represent common traits, a disease or group of related diseases and conditions.

Once you find an ICD-10 code in the Alphabetic Index, you’ll need to review the code details and instructions in the Tabular List to confirm that it’s the right diagnosis code and to code it properly.

In the chapters listed above, notice the code ranges included in the titles. These sets of alphanumeric characters further define the chapter title by telling you the categories contained within it.

You may need to code for a patient with a history of retinopathy, for instance. In the Alphabetic Index, you see Retinopathy (background) H35.00 and find the code details, as expected, in the chapter dedicated to diseases of the eye.

But if your patient has diabetic retinopathy, the Index will offer several code options in the E08-E13 range, which will then direct you to Chapter 4 Endocrine, Nutritional and Metabolic Diseases (E00-E89).

Additionally, the code range within each chapter in the Tabular List is broken down into subchapters called blocks, similar to the following block summary from Chapter 4.

• E00-E07 Disorders of thyroid gland
• E08-E13 Diabetes mellitus
• E15-E16 Other disorders of glucose regulation and pancreatic internal secretion
• E20-E35 Disorders of other endocrine glands
• E36 Intraoperative complications of endocrine system
• E40-E46 Malnutrition
• E50-E64 Other nutritional deficiencies
• E65-E68 Overweight, obesity and other hyperalimentation
• E70-E88 Metabolic disorders
• E89 Postprocedural endocrine and metabolic complications and disorders, not elsewhere classified

Each block contains one or more categories, many of which are divided into subcategories in the ICD-10 Tabular List.

In the example below, E13 is a category. E13.0, E13.1, E13.2, and E13.3 are subcategories, as are E13.31 and E13.32.

E13 (Other specified diabetes mellitus)

• E13.0 (Other specified diabetes mellitus with hyperosmolarity)
  • E13.00 (... without nonketotic hyperglycemic-hyperosmolar coma (NKHHC))
  • E13.01 (... with coma)
• E13.1 (Other specified diabetes mellitus with ketoacidosis)
  • E13.10 (... without coma)
  • E13.11 (... with coma)
• E13.2 (Other specified diabetes mellitus with kidney complications)
  • E13.21 (Other specified diabetes mellitus with diabetic nephropathy)
  • E13.22 (Other specified diabetes mellitus with diabetic chronic kidney disease)
  • E13.29 (Other specified diabetes mellitus with other diabetic kidney complication)
• E13.3 (Other specified diabetes mellitus with ophthalmic complications)
  • E13.31 (Other specified diabetes mellitus with unspecified diabetic retinopathy)
    • E13.311 (... with macular edema)
    • E13.319 (... without macular edema)
  • E13.32 (Other specified diabetes mellitus with mild nonproliferative diabetic retinopathy)
    • E13.321 (Other specified diabetes mellitus with mild nonproliferative diabetic retinopathy with macular edema)
      • E13.3211 (... right eye)
      • E13.3212 (... left eye)
      • E13.3213 (... bilateral)
      • E13.3219 (... unspecified eye)

Note that ICD-10 coding employs a decimal point following the category and preceding the subcategory. Every character to the right of the decimal point adds specific information about the diagnosis.

Among the diagnosis codes listed above in the E13 category, none are the same. Each ICD-10 code represents a unique diagnosis. That’s why you must always assign subdivisions until you have coded to the highest level of specificity when reporting ICD-10 codes to payers, claims clearinghouses, or billing and collection agencies.

The 7^th Character in ICD-10 Coding

Not all ICD-10 codes require a 7^th character, but when they do, the 7^th character serves a particular purpose—like signifying laterality or defining whether the code represents an initial encounter for the problem, a subsequent encounter, or a sequela arising from another condition.

In the E13 category, codes demonstrating laterality for E13.321 are shown with the 7^th character added. Your ICD-10 code book, however, will merely provide instructions to add the 7^th character, such as:

One of the following 7^th characters is to be assigned to codes in subcategory E13.32 to designate laterality of the disease:

Because the 7^th character is required to correctly code E13.321, option “9 - unspecified eye” is included in the event that clinical documentation doesn’t indicate which eye is affected.

Coding the 7^th Character with Placeholder “X”

Another scenario you’ll encounter when reporting diagnoses on medical claims is codes requiring a 7^th character that don’t have six characters at their height of specificity. This is where placeholder “X” comes into play.

ICD-10-CM placeholder “X” was created to accommodate expansion of the code set with anticipation that characters with specific meanings will eventually occupy the designated spaces. In the interim, medical coders are required to use placeholder “X” to fill in the missing character(s), thereby preserving the diagnosis code classification structure.

For codes with less than 6 characters that require a 7^th character, the placeholder “X” should be assigned for all absent characters. In other words, the 7^th character must always be the 7^th character. A code is invalid if you don’t add the “X” to hold the place of the 4^th, 5th, or 6th character before adding the 7^th.

Some code examples using ICD-10 placeholder “X” include:

• T18.1 (Foreign body in esophagus) becomes T18.1XXS (Foreign body in esophagus, sequela)
• H40.10 (Unspecified open-angle glaucoma) becomes H40.10X3 (Unspecified open-angle glaucoma, severe stage)

ICD-10-PCS Basics

The PCS in ICD-10-PCS stands for procedural classification system. This inpatient medical code set has a logical, consistent structure that follows a logical, consistent process down to each character level in each code. Medical coders will find constructing codes in ICD-10-PCS equally logical and consistent.

While incorporating input from organizations, physicians, and researchers, the design of ICD-10-PCS follows recommendations from the National Committee on Vital and Health Statistics (NCVHS). ICD-10-PCS is completely separate from ICD-10-CM. Moreover, ICD-10-PCS is quite distinct from CPT^®  — the other procedural code set used to report services and procedures in outpatient healthcare settings.

Structural attributes of ICD-10-PCS include:  

• Standardized Level of Specificity — Each of the seven alphanumeric characters in an ICD-10-PCS code define procedure details such as body part, approach, and device used. Each ICD-10-PCS code creates its descriptor, and all descriptors are uniform, covering the same type and level of specificity.
• Unique — A unique code is available for each significantly different procedure, and each code retains its unique definition. Codes are not reused or modified. The same procedure performed on a different body part, for instance, has its own code. Similarly, every procedure that uses a different approach has a unique code.
• Expandability — The structure of PCS is designed to accommodate emerging procedures and technologies and allow for the creation of new codes without disrupting the system. Hint: a whole code is never added to PCS, but rather a new value for a character is added.
• Standardized Terminology — Just as characters and values are defined within the system, the terminology used in ICD-10-PCS is standardized to provide precise and stable definitions of all procedures. For example, in medical operative report terminology, the word excision describes a variety of surgical procedures. When coding in PCS, excision describes a single, precise surgical objective, “To cut out or off, without replacement, a portion of a body part.” 

ICD-10-PCS System Organization

ICD-10-PCS is composed of 17 sections, represented by the numbers 0–9 and the letters B–D, F–H and X. The broad procedure categories contained in these sections range from surgical procedures to substance abuse treatment and new technology.

The 17 ICD-10-PCS Sections

Medical and Surgical Section: All procedure codes in the Medical and Surgical section begin with the section value 0. The Medical and Surgical section contains the majority of PCS codes — 67,655 of a total 78,103 codes — all of which are used solely in U.S. inpatient, hospital settings.

Medical and Surgical Related Sections: Sections 1–9 of ICD-10-PCS comprise the Medical and Surgical Related sections. These sections include obstetrical procedures, administration of substances, measurement and monitoring of body functions, and extracorporeal therapies.

Ancillary Sections: Sections B–D and F–H comprise the ancillary sections of ICD-10-PCS. These six sections include imaging procedures, nuclear medicine, and substance abuse treatment.

Structure of PCS Codes

All ICD-10-PCS codes consist of seven characters. Each character can be one of 34 values — the numbers 0-9 and the letters of the alphabet, minus O and I (to avoid confusion with numbers zero and one). The 34 possible character values give ICD-10-PCS vast potential, in that the same character value in a different character position carries a different meaning.

Each character position in the PCS represents a category of information about the procedure. From the Medical and Surgical section, character positions represent the following categories of information:

For example, consider ICD-10-PCS code 0LB50ZZ Excision of right lower arm and wrist tendon, open approach.

The Significance of Character Position in PCS Codes

Within the code range of a section, categories of information for each character position remain stable. For example, the 5^th character retains the general meaning approach in sections 0–4 and 7–9 of the system. The value assigned to the 5^th character in these sections will always define a specific approach, such as open.

Each group of values for a character contains all valid choices. In the 5^th character, for example, each significantly distinct approach is assigned a unique value and all applicable approach values are included to represent the possible versions of a procedure.

But not all PCS sections have the same character positional categories. While codes in sections 3-9 are structured similarly to the Medical and Surgical section, there are a few exceptions. In sections 5 and 6, for example, the 5^th character is defined as duration instead of approach, as in this code for intra-aortic balloon pump (IABP):

Additional differences include these uses of the 6^th character:

• Section 3 defines the 6^th character as substance.
• Sections 4 and 5 define the 6^th character as function.
• Sections 7 through 9 define the 6^th character as method.

The categories of information for some characters in the ancillary sections differ, as well. In the Imaging section, the 3^rd character is defined as root type, and the 5^th and 6^th characters define contrast and contrast/qualifier respectively, as in the CT scan example below.

Other differences in the ancillary section include:

• Section C defines the 5^th character as radionuclide.
• Section D defines the 5^th character as modality qualifier and the 6th character as isotope.
• Section F defines the 5^th character as type qualifier and the 6th character as equipment.
• Sections G and H define the 3^rd character as a root type qualifier.
• Section X defines the 7^th character as the new technology group. This letter changes each year that new technology codes are added to the system. For example, Section X codes added for the first year have the 7^th character value 1, New Technology Group 1. The next year that contains new Section X codes the 7^th character value is 2, for New Technology Group 2, etc.

Think of ICD-10-PCS codes as the result of a process rather than as an assigned number. The process constructs the PCS code based on details about the procedure. Values for each character specify information according to each character’s position.

Using PCS Tables

To construct complete and valid codes in ICD-10-PCS, you will refer to the Tables. You can locate these with the first three code values provided in the Index.

PCS Tables are organized in alphanumeric order in a series by Section, which is the first character of a code. Tables that begin with 0 to 9 are listed first, then Tables beginning with B-D, then letters F-X, are listed next. The same convention is followed within each Table for the 2^nd through the 7^th characters — numeric values in order first, followed by alphabetical values.

The root operation Tables consist of four columns and a varying number of rows. The values for characters 1 through 3 (Section, Body System, and Root Operation) are provided at the top of each Table, and the Table itself contains columns with the applicable values for characters four through seven, as seen in the example of the root operation bypass, in the central nervous body system.

A Table may be separated into rows to specify the valid choices of values in characters four through seven. A code built using values from more than one row of a Table is invalid code. In the Table above, there are only five choices for the 7^th character of Body Part, U, Spinal Canal. You can’t cross the line to choose a 7^th character from the row above.

In ICD-10-PCS, each character defines information about the procedure and all seven characters must contain a specific value. Even values such as the 6^th character value Z, No device and the 7^th character value Z, No qualifier, provide important information about the procedure performed.

Build-A-PCS Code

Find the complete ICD-10-PCS code for laparoscopic cholecystectomy to remove the entire gallbladder.

• 1.

  Look in the Index for Main term cholecystectomy.
  
  Cholecystectomy
  see Excision, Gallbladder 0FB4
  see Resection, Gallbladder 0FT4
  Refer to Root Operations table to review definitions for excision and resection.
  

• 2.

  Since the scenario documents removing the entire gallbladder, refer to main term, resection for cutting out all of a body part.

• 3.

  Refer to Table 0FT.

Section:                0 Medical and Surgical

Body System:       F Hepatobiliary System and Pancreas

Operation:           T Resection: Cutting out or off, without replacement, all of a body part

• 4.

  The 4^th character was listed in the Index as 4. Confirm in the table that 4 represents gallbladder.

• 5.

  Select the 5th character, approach. Stay in the same row as the gallbladder. Crossing over into another row can cause the coder to form an invalid code. This gives two choices: 0 for open and 4 for percutaneous endoscopic. The example states the approach is laparoscopic. A laparoscope is inserted percutaneously through the abdominal wall. Thus, the correct choice is 4 Percutaneous Endoscopic.

• 6.

  Select the 6th and the 7th characters. These characters have only one option to choose from — Z No Device and Z No Qualifier.

• 7.

  Put all 7 characters together to get the complete ICD-10-PCS code: 0FT44ZZ.

NOTE: If you had searched for the main term, laparoscopic, the ICD-10-PCS Index entry would have led you to: Laparoscopy see Inspection

The definition for Inspection is visually and/or manually exploring a body part. This definition does not fit our example of surgically removing the entire gallbladder using a laparoscope. The coder should therefore search for a better main term for the root operation or body part effected. This illustrates that one of the first steps for PCS coding is to study the root operations so that you understand their meaning. This will make it easier to start your search for the main term.