Which classification System was developed by the World Health Organization

International Classification of Diseases (ICD)-10-CM Codes

The International Classification of Diseases, now in its tenth revision (ICD-10), is the taxonomy used by all healthcare professionals and insurers in the United States when discussing medical conditions.14 The version of ICD-10 used for billing purposes in the United States is “clinical modification” (CM). (For example, in ICD-10-CM “speak,” gross hematuria is R31.0 [the fourth and fifth digits denote gross, microscopic, or unspecified], and a solitary thyroid nodule is E04.1.) ICD-10-CM coding is used to determine whether a procedure billed to an insurer is medically necessary, in which case it is a covered benefit for the patient. With the passage of the Medicare Catastrophic Coverage Act of 1988, diagnostic coding using the previous version (ICD-9-CM) became mandatory for Medicare claims, and when HIPAA was implemented in 2003, ICD-CM coding became universal, meaning that private insurers, as well as government agencies, are required to use it. For convenience, hereinafter we refer to ICD-10-CM simply as ICD-10.

In the United States, all healthcare providers must furnish an ICD-10 code to justify the medical necessity of a diagnostic test. For example, if a urine cytology test is ordered for a patient with gross hematuria, the patient’s physician will furnish ICD-10 code R31.0, which denotes gross hematuria, on the requisition form that accompanies the urine specimen. Similarly, when your laboratory bills an insurer for having performed a cytologic examination of a specimen, the bill must include an appropriate ICD-10 code to justify the medical necessity of the test. (It might be the same “clinical code” you received from the ordering physician, or it might be different, a “pathologic code,” as discussed below.) Payers have lists of approved ICD-10 codes for many laboratory tests, and will deny payment if anon-approved code is provided. In the example above, if you supply a wrong ICD-10 code, like R51 (denoting “headache”) with the bill for the urine cytology, it is likely that Medicare will deny the claim because R51 doesn’t justify the medical necessity of urine cytology. Pointers for selecting the appropriate ICD-10 code for cytology specimens are provided below.

The provider who sends a cytology sample to the laboratory does not have to provide a literal ICD-10 code. It is acceptable for the referring physician to write a narrative diagnosis (e.g., “gross hematuria”) on the requisition form, which the laboratory can then translate into an ICD-10 code (in this example, R31.0) by consulting the codebook.

The ICD-10 codebook consists of 3 volumes used by providers and hospitals billing foroutpatient services. Inpatient services are billed using the coding system established under ICD-10-PCS. The index is an alphabetical list of the conditions for which a diagnosis code has been assigned. Volume 1 is the Tabular List which arranges all diagnosis codes numerically within 21 chapters based on body system or nature of disease. Volume 2 is the instruction manual providing explanations of the conventions and guidelines regulating the assignment of diagnosis codes. The final, unnumbered volume is the alphabetical index of diseases arranged alphabetically by disease, illness, injury, or other descriptive diagnostic term. ICD-10-CM is distributed by the National Center for Health Statistics, a branch of the CDC. You need to be alert for changes in the ICD-10 codes (i.e., watch the CMS and professional associations’ websites) because the codes are eligible for update twice a year (April 1 and October 1). ICD-10-PCS, with rules for inpatient coding, is not of concern to pathologists and independent labs.

Comparison of Codes

When ICD-9 and ICD-10 are compared, there are several differences in nomenclature that are immediately obvious. ICD-9-CM codes are three to five characters in length, while ICD-10-CM codes are three to seven characters in length. ICD-9-CM encompassed just in excess of 14,000 codes, but ICD-10-CM will have over 69,000 codes to start. Implicit in this coding redesign, ICD-10-CM will have increased flexibility for adding new codes when compared to ICD-9-CM. To accommodate this increase, where ICD-9-CM coding consists of a first character that could be alphanumeric (first character E or V or numeric), ICD-10-CM consists of a first character that can be alphanumeric, characters 2 and 3 that are numeric, and characters 4 through 7 that can be alphanumeric. By calculation, ICD-10-CM can potentially accommodate close to 375,000 codes. With the ability to code for numerous contingencies, ICD-10-CM can be very specific and detailed. Where ICD-9-CM lacked the ability to distinguish laterality, the ICD-10-CM language can distinguish between left- and right-sided diagnoses (CMS, 2013; Topaz et al., 2013; WHO, 2013c).

Medicare Payment for Imaging Technology, International Classification of Diseases-10, and Current Procedural Terminology Coding

Medicare may issue a national coverage determination for a type of imaging study, such as magnetic resonance imaging (MRI). For technology that Medicare has not made a national coverage decision, it allows the local contractors (local administrators of Medicare) to decide if they wish to cover costs related to the use of that technology.

Medicare reimburses for services, imaging, or procedures if they are used for anapproved medical indication. The medical indication is determined by a series of codes for symptoms and diseases, which are taken from the International Classification of Diseases (ICD), which is now in its 10th edition (ICD-10). ICD-10 only very recently supplanted ICD-9, the former version of the coding system. ICD-10 introduced a great deal of increased complexity to the coding system for symptoms and diseases, a change that had significant ramifications for radiology practices.

The ICD-10 codes define medical necessity, that is, why an imaging study was used. What was actually done for the patient is based on the CPT coding. New or revised CPT codes must be approved by the CPT Editorial Panel, selected by the American Medical Association’s Board of Trustees, based on recommendations from diverse stakeholders such as specialty societies, industry, or the general public. CPT codes determine the medical service (cognitive, imaging, and procedural) actually performed.

There are three categories of CPT codes. Category 1 codes are for services that are common and backed by evidence. An example is CT of the chest with contrast to diagnose pulmonary embolus. Category 2 codes are supplementary tracking codes that help with performance measures and compliance. Category 3 codes are used for new and emerging technologies that are yet to be approved by the Food and Drug Administration or those for which more research is needed.

Once a CPT code has been approved, it is sent to the RUC, which decides on the relative value of the code under the RBRVS. The RUC determines the relative value of the physician work and sends its conclusions as a recommendation to CMS. Thus, the RUC acts as an unofficial advisor to CMS in determining the level of payment for particular imaging technologies and applications. CMS may choose to follow or ignore the recommendations of the RUC. By law, however, CMS must evaluate the relative value of each procedure every 5 years. In 2006, the CPT Editorial Panel and RUC formed the Relativity Assessment Workgroup to help CMS identify misvalued codes. In general, theupdated relative values of medical imaging have resulted in lowering payments to physicians and hospitals.

International Classification of Diseases (ICD)

The aim of the ICD is to categorize diseases, health-related conditions, and external causes of disease and injury in order to be able to compile useful statistics in mortality and morbidity. Its categories are also useful for decision support systems, reimbursement systems, and as a common denominator to be used in language-independent documentation of medical information.

The history of the systematic statistical classification of diseases dates back to the nineteenth century. Groundwork was done by early medical statisticians, such as William Farr (1807–83) and Jacques Bertillon (1851–1922). The French government convened the first International Conference for the revision of the Bertillon or International Classification of Causes of Death in August 1900. The next conference was held in 1909, and the French government called succeeding conferences in 1920, 1929 and 1938. With its sixth revision in 1948, WHO became the custodian of the ICD. The ICD-6 extended the scope of the classification to nonfatal diseases, and WHO has continued to be responsible for periodic revisions of the classification. With a need to create comparability at the international level in public health as well as in clinical research, more and more clinical concepts have been introduced. The current revision, the ICD-10, consists of three volumes, and for correct coding all three volumes are necessary. Volume I contains the tabular list, as well as some definitions and the WHO nomenclature regulations. Volume II is the manual with extensive description of the classification and methods for use in mortality and morbidity, including short lists. Volume III is the alphabetical index. It contains separate indices for diseases, external causes, and drugs/substances.

Since its publication in 1992, an updating mechanism allows yearly updates and major revisions every 3 years. However, the structure and the content of ICD-10 are mainly based on scientific knowledge at the time of its creation, as well as on previous editions, and deserve thorough revision. The revision process toward ICD-11 started in 2006 for publication by 2015 (Ustun et al., 2007; World Health Organization, International Classifications, 2007).

ICD-10 can be looked up online in English and French at WHO (World Health Organization, International Classifications, 2007), and accessed in other languages through the relevant national institutions (WHO Collaborating Centers for the Family of International Classifications, 2007). Overall, ICD-10 is available in 42 languages.

Some countries have created clinical modifications for morbidity applications, principally as extensions of the international classification. Special adaptations have been created by medical scientific societies for clinical and research use in the relevant specialties (see Modifications and Adaptations).

Implementation

ICD-10 has been implemented in the majority of WHO Member States as the standard for coding diseases in mortality and/or morbidity (statistics, reimbursement, resource allocation, administration, treatment, and research), and ICD is in the process of being implemented in many other Member States. For example, the ICD is used in systematic full mortality registration in more than 117 countries, as displayed in Figure 3. However, implementation is not easily defined, because it gives no indication of the level of use of ICD-10 within the whole health sector. For example, a government might decide to implement ICD-10 for coding mortality; however, this represents only a fraction of the use of ICD-10 within a health system, and use in morbidity may relate only to pilot projects or specific diseases. If a country has fully implemented ICD-10 at a national level, this would mean that it has mandated the use of ICD-10 for coding mortality and morbidity across the whole health sector, as in the United Kingdom, South Africa, and many other countries. This means that all health-care providers (or the appropriate allied personnel) will be required to code every death and every patient discharge, thus using ICD-10 for death registration, claims, and reimbursement purposes. In these cases, if the health-care providers do not use ICD-10 codes on their claims, their claims will be rejected.

Figure 3. Registration of causes of death mortality (since 1995) with cause of death available to WHO.

Implementation

ICD-10 has been implemented in the majority of WHO Member States as the standard for coding diseases in mortality and/or morbidity (statistics, reimbursement, resource allocation, administration, treatment, and research), and ICD is in the process of being implemented in many other Member States. For example, the ICD is used in systematic full mortality registration in more than 117 countries. However, implementation is not easily defined, because it gives no indication of the level of use of ICD-10 within the whole health sector. For example, a government might decide to implement ICD-10 for coding mortality; however, this represents only a fraction of the use of ICD-10 within a health system, and use in morbidity may relate only to pilot projects or specific diseases. If a country has fully implemented ICD-10 at a national level, this would mean that it has mandated the use of ICD-10 for coding mortality and morbidity across the whole health sector, as in the UK, South Africa, and many other countries. This means that all health care providers (or the appropriate allied personnel) will be required to code every death and every patient discharge, thus using ICD-10 for death registration, claims, and reimbursement purposes.

5.2 ICD-10

The International Classification of Disease (ICD) was developed by the World Health Organization (WHO). The first ICD classification originated in the 19th century and has expanded with medical knowledge. ICD-9 has been used to report medical diagnoses and inpatient procedures, and has been integrated into the United States healthcare system for 30 years. ICD-10 involves a complete restructuring and significant expansion of the clinical codes to accommodate new diseases, technological changes, and ongoing advancement in clinical care. The majority of countries use ICD-10, the United States being one of the last adopters. The United States is expected to transition to ICD-10 on October 1, 2015.

ICD-10 System of Classification of Mental Disorders

The ICD is the result of an effort to create a universal diagnostic system that began at an international statistical congress in 1853 with an agreement to prepare the causes of death for common international use. Subsequently, periodic revisions were made and, in 1948, when the World Health Organization was formed, the sixth revision of the ICD was produced. Since this date, Member States have decided to use the ICD in their national health statistics. The sixth revision of the ICD for the first time contained a separate section on mental disorders. Since then, extensive efforts have been undertaken to better define mental disorders. Work on the ICD Chapter V for mental disorders has been significantly supported by international work, mainly by the development of the DSM of Mental Disorders (American Psychiatric Association, 1994). There has been a synchrony between ICD-6 and DSM-I, ICD-8 and DSM-II, ICD-9 and DSM-III, ICD-10, DSM-IV, and DSM-5 with increasing harmony and consistency between the two thanks to the international collaboration between WHO, APA, WPA, and a large network of international collaborative centers. Similarly, work on national classificatory systems, such as the Chinese Classification of Mental Disorders in China, the Latin American Guide for Psychiatric Diagnosis, and the Cuban Glossary of Psychiatry have been standardized with ICD-10 Chapter V, forming a useful internationally comparable yet culturally adapted system.

In the most recent 10th revision of the ICD (ICD-10), the mental disorders chapter has been considerably expanded and several different descriptions are available for the diagnostic categories: The clinical description and diagnostic guidelines (CDDGs) (World Health Organization, 1992), a set of diagnostic criteria for research (DCR) (World Health Organization, 1993), diagnostic and management guidelines for mental disorders in primary care (PC) (World Health Organization, 1996), a pocket guide (Cooper, 1994), a multiaxial version (World Health Organization, 1997), and a lexicon (World Health Organization, 1989). These interrelated components all share a common foundation of ICD grouping and definitions yet differentiate to meet the needs of different users.

In the ICD-10, explicit diagnostic criteria and rule-based classification have replaced the art of diagnosis with a reliable and replicable descriptive scheme that has considerable predictive validity in terms of effective interventions. Its development has relied on international consultation and has been linked to the development of assessment instruments. The mental disorders chapter of the ICD-10 has undergone extensive testing in two phases to evaluate the CDDGs (Sartorius et al., 1993) as well as the DCR (Sartorius et al., 1995), and agreement between different assessors as measured by the kappa statistic for most categories was over 0.70, indicating very good agreement. Low agreement categories were later revised so as to improve the reliable use of the classification.

International classification of diseases (ICD)

The ICD (https://www.who.int/classifications/icd/factsheet/en/) is a well-known medical classification system for diseases and medical conditions. It provides codes for diagnoses, signs and symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or diseases. Currently valid in many countries is ICD-10 with country-specific modifications. ICD-10 codes might have up to seven characters:

Characters 1–3 = Indicate the category of the diagnosis

Characters 4–6 = Indicate etiology, anatomic site, severity, or other clinical details

Character 7 = Extensions

The main category is encoded in the first character by a capital letter while characters 4–7 add additional specificity to the code. The list of main categories is shown in Table 2. In Fig. 5 an excerpt from the ICD-10 hierarchy can be seen.

Table 2. ICD-10 Main categories.

A & B: Infectious and Parasitic Diseases
C: Neoplasms
D: Neoplasms, Blood, Blood-forming Organs
E: Endocrine, Nutritional, Metabolic
F: Mental and Behavioral Disorders
G: Nervous System
H: Eye and Adnexa, Ear and Mastoid Process
I: Circulatory System
J: Respiratory System
K: Digestive System
L: Skin and Subcutaneous Tissue
M: Musculoskeletal and Connective Tissue
N: Genitourinary System
O: Pregnancy, Childbirth and the Puerperium
P: Certain Conditions Originating in the Perinatal Period
Q: Congenital Malformations, Deformations and Chromosomal Abnormalities
R: Symptoms, Signs and Abnormal Clinical and Lab Findings
S, T: Injury, Poisoning, Certain Other Consequences of External Causes
U: used for emergency code additions
V, W, X, Y: External Causes of Morbidity
Z: Factors Influencing Health Status and Contact with Health Services

The 11th edition of ICD, ICD-11, was adopted in May 2019. However, an official implementation in single countries is still on its way.

Application of the ICD to Neurology

The Application of the ICD to Neurology (ICD-10-NA) is an expansion of the original ICD-10 with further detailed classification of diseases of neurological origin or expression. It also contains a table of inclusion and exclusion terms and a detailed alphabetical index. The coding system of the ICD-10-NA is exactly the same as for the ICD-10, since cross-referencing requires that specialization classifications such as the ICD-10-NA derived from the ICD must have the same three- and four-digit codes as those in the original ICD-10. Within these limits, the fifth, sixth, and seventh digits of the subdivision codes, and the generalization of multiple coding used to describe both etiologies and manifestations, have greatly increased the discriminating power and precision of neurological diseases classification based on the parent ICD.

Conversion disorder in the international classification of diseases (ICD)

The International Classification of Diseases started out as the International List of Causes of Death. It was not until the sixth edition that it became a classification of diseases and injuries. ICD-6 (World Health Organization, 1948) divided psychoneuroses into those “without mention of somatic symptoms” and those “without mention of anxiety reaction.” Within the latter category, listed under “hysteria” were a number of hysterical neurologic symptoms, including amnesia, anesthesia, anosmia, aphonia, blindness, convulsions, dyskinesia, mutism, paralysis, postures, tic, and tremor. Also on this list were “conversion” and “hysteroepilepsy,” without explanation as to how these related to the other neurologic symptoms. ICD-7 (World Health Organization, 1957) changed terminology to “psychoneurosis with somatic symptoms affecting other systems.” The systems designated included respiratory, genitourinary, cutaneous, and musculoskeletal (which included paralysis). This seems to have been a blurring of the boundary between psychophysiologic disorders and hysterical conversion. The other specific hysterical neurologic symptoms listed in ICD-6 no longer appeared in the classification.

The term “conversion” first appeared in ICD-8 (World Health Organization, 1968) as “conversion hysteria,” a subtype of hysterical neurosis. Similarly, ICD-9 (World Health Organization, 1975) listed “conversion hysteria” as a subtype of hysteria. “Conversion disorder” first appeared in a later version, ICD-9-CM (World Health Organization, 1979). Conversion disorder was listed under the category titled “dissociative, conversion and factitious disorders,” with subtypes of hysterical astasia-abasia, blindness, deafness, paralysis, and conversion hysteria or reaction. ICD-10 (World Health Organization, 1992) grouped dissociative and conversion disorders together, listing the diagnosis as “dissociative (conversion) disorder.” In the current edition of ICD-10 (World Health Organization, 2016), conversion disorder is listed under dissociative and conversion disorders, with subtypes of motor symptom or deficit, seizures or convulsions, and sensory symptom or deficit.

One recent proposal for ICD-11 is to bring conversion back within the primary domain of neurology as functional neurologic disorders within the neurologic section of ICD (Stone et al., 2014). Like other conditions shared between neurologists and psychiatrists (e.g., Tourette syndrome and dementia), psychiatry would retain a code for functional neurologic disorders, ideally matching the one in neurology. The proposal aims to encourage neurologists to take clinical responsibility for these patients, making positive diagnoses rather than by exclusion; incorporate functional disorders into neurologic education; encourage neurologists to engage in related research; and promote collaboration between neurologists and psychiatrists.