Whenever a patient sees a healthcare provider, the provider documents their visit, reviews the complaint and medical history, makes an expert assessment of the condition, and proposes treatment. This process involves the use of medical codes.

Medical codes are a term referring to diseases, symptoms, diagnoses, prescriptions, treatments, services, and other medical procedures a doctor or healthcare provider performs on a patient. These codes tell the patients, medical workers, insurances, and other involved participants more about the diagnoses, provided services, and how much they cost.

Different categories of medical codes

There are two primary groups of medical codes:

1. CPT Codes

‘Current Procedural Terminology’ or CPT refers to standard codes used in most contemporary medical settings. These codes describe each type of service a healthcare provider carries out on a patient, including evaluations, tests, surgeries, and so on.

They are mainly used to enable reimbursement by submitting to insurance, Medicare, or another payer. Patients can also use them to better understand the services they received, check for any issues in their bills, or to try to (re)negotiate the prices for the services.

2. ICD Codes

Short for ‘International Classification of Diseases and Related Health Problems’, ICD refers to a medical classification list whose publication is authorized by the World Health Organization (WHO). The list serves for classifying diseases, illnesses, injuries, health encounters, and inpatient procedures in morbidity settings.

Primary users of ICD codes are healthcare professionals, like physicians and nurses, but also medical coders who assign ICD codes to diagnosis or procedure information. The codes are used for various purposes, including for billing and claims reimbursement, as well as in statistics.

Secondary users of ICD codes are people who already use coded data from hospitals, healthcare providers, or health plans to carry out research and monitoring activities. Public health is one example of a secondary user of ICD codes.

Other groups of medical codes include:

3. HCPCS Codes

The lesser-known category of medical codes, used by Medicare, is Healthcare Common Procedure Coding System or HCPCS. This system draws on CPT codes and is useful to patients using Medicare, especially those in need of ambulance services or other resources outside of their doctor’s office. There are two levels of HCPCS codes:

  • Level I: these codes mirror CPT codes and denote medical procedures and services a physician or another licensed professional has ordered.
  • Level II: these are alphanumeric and denote non-physician services such as ambulance rides, walkers, wheelchairs, and other kinds of durable medical equipment, as well as other medical services that Level I doesn’t cover.

4. ICF Codes

Short for the ‘International Classification of Functioning, Disability, and Health’, ICF codes measure and describe the level of health and disability in connection to a certain health condition. While the ICD codes classify an illness, the ICF codes measure how the affected person is functional in their environment.

5. DRG Codes

The ‘diagnostic-related group’ or DRG system ‘groups together’ different medical codes for hospital billing purposes. This system categorizes hospital services based on a diagnosis, treatment, and other relevant criteria. 

It allows hospitals to get paid for inpatient services on the basis of a patient’s assigned DRG profile at a fixed rate, regardless of the actual cost of the hospital stay or how much the hospital bills the insurance company or Medicare. 

There are around 500 different DRGs, assuming the same patient profile requires roughly the same treatment.


6. NDC Codes

The National Drug Code or NDC indicates nonprescription (OTC) and prescription medications. It is a 10-digit numeric code that is visible on all medication packages in the US and includes three parts:

  • identifying the medication labeler (manufacturer, repackager, distributor, or marketer)
  • identifying the medication (strength, formulation, and dosage form)
  • identifying the size and type of the medication package

Although the US Food and Drug Administration (FDA) manages and updates the NDC Directory daily, the medications on the list aren’t necessarily approved by it.

7. CDT Codes

Like its name indicates, the Code on Dental Procedures and Nomenclature (CDT) has a role in oral health and related dentistry services, allowing dental professionals to have a set of procedural alphanumeric codes for their work.

The American Dental Association (ADA) annually publishes the CDT reference manual, categorizing the codes according to the type of service: diagnostic, restorative, preventive, periodontics, endodontics, removable prosthodontics, maxillofacial prosthetics, implant services, fixed prosthodontics, implant services, maxillofacial surgery, orthodontics, and adjunctive general services.

8. DSM Codes

The American Psychiatric Association (APA) publishes and maintains the Diagnostic and Statistical Manual of Mental Disorders. The codes in this manual (the latest edition is DSM-5) are used by mental health professionals and other relevant entities to diagnose, describe, and classify psychiatric illnesses.

That said, the newest edition of the manual recommends using ICD-10 codes for psychiatric conditions instead. The existing patient records may still include the DSM codes.

Now, let’s inspect the two major categories – CPT and ICD codes.

What are CPT codes

Developed by the AMA, the Current Procedural Terminology (CPT) codes are vital in billing medical services, as well as the procedures for their reimbursement. Providers of medical services (physicians, hospitals, laboratories, outpatient facilities, non-physician practitioners, and allied health professionals) use these codes to describe and report services and procedures to private and federal payers.

Through its CPT Editorial Panel, the American Medical Association (AMA) maintains and annually updates the list of CPT codes. These codes include five characters which are typically numeric, but some of them include a fifth alpha character. 

There are three categories of CPT codes:

  • Category I: Five-digit codes that include descriptions of a procedure or service (most CPT codes are in this category)
  • Category II: Supplemental alphanumeric tracking codes referring to performance evaluation or clinical services with no relative value
  • Category III: Temporary codes assigned to tracking the efficacy of emerging and experimental technologies, procedures, and services

Category I CPT codes are divided into six main sections:

  1. Evaluation and Management: 99201 – 99499
  2. Anesthesia: 00100 – 01999; 99100 – 99140
  3. Surgery: 10021 – 69990
  4. Radiology: 70010 – 79999
  5. Pathology and Laboratory: 80047 – 89398
  6. Medicine/Medical Services and Procedures: 90281 – 99199; 99500 – 99607

Each of these sections further includes its own subfields.

Category II of CPT codes is not associated with any relative value, so the services in this group are billed with a $0.00 billable charge amount. The Performance Measures Advisory Group (PMAG), which is an advisory body to the CPT Editorial Committee and the CPT/HCPAC Advisory Committee, reviews the codes in accordance with the medical and additional expertise. This category includes 10 sections:

  1. Composite Measures: 0001F – 0015F
  2. Patient Management: 0500F – 0584F
  3. Patient History: 1000F – 1505F
  4. Physical Examination: 2000F – 2060F
  5. Diagnostic/Screening Processes or Results: 3006F – 3776F
  6. Therapeutic, Preventive, or Other Interventions: 4000F – 4563F
  7. Follow-up or Other Outcomes: 5005F – 5250F
  8. Patient Safety: 6005F – 6150F
  9. Structural Measures: 7010F – 7025F
  10. Non-measure Listing: 9001F – 9007F

Since it covers emerging technologies only, Category III contains temporary CPT codes (which stay there for up to five years). They range from 0016T-0207T and these codes may become Category I codes if the CPT Editorial Panel approves them. The AMA releases on its website new or revised codes from Category III semi-annually, while it publishes deletions annually, along with the full listing of temporary codes.

The most common CPT codes

Some of the CPT codes occur more frequently than the others, for instance:

  • 99214 – established patient office or other outpatient services
  • 47350 – simple repair of liver hemorrhage
  • 47360 – complex liver repair procedure, with or without hepatic artery ligation
  • 62000 – elevation of a simple, extradural depressed skull fracture
  • 62005 – elevation of a compound or commuted, extradural depressed skull fracture
  • 3008F – Body Mass Index (BMI), documented
  • 0001F – heart failure assessed
  • 0503F – postpartum care visit
  • 1030F – pneumococcus immunization status assessed
  • 2014F – mental status assessed
  • 3006F – chest X-ray documented and reviewed
  • 4037F – influenza immunization ordered or administered
  • 5005F – patient directed to perform self-examination for new or changing moles
  • 6015F – patient received or is allowed to receive foods, fluids, or medication by mouth
  • 7025F – patient data input in the reminder system with a date for the next mammogram
  • 0123T – fistulization of sclera for glaucoma, through the ciliary body

The most common psychiatric CPT codes

Some CPT codes appear regularly in psychiatry, such as:

  • 90791 – psychiatric diagnostic evaluation without medical services
  • 90792 – psychiatric diagnostic evaluation with medical services
  • 90832 – psychotherapy, 30 minutes
  • 90833 – evaluation and management with 30 minutes psychotherapy
  • 90846 – family psychotherapy, without patient present
  • 90847 – family psychotherapy, with patient present
  • 90839 – psychotherapy in crisis
  • 99203 – new patient, outpatient, in-office services, 30 minutes
  • 99215 – established patient, outpatient, in-office services, 40 minutes
  • 99242 – new or established patient, outpatient, consultation, 30 minutes
  • 99252 – inpatient consultation, 40 minutes
  • 90865 – narcosynthesis
  • 90870 – electroconvulsive therapy (ECT)
  • 90885 – psychiatric evaluation of records

For the full list of CPT codes check this link.

What are ICD codes

The International Classification of Diseases and Related Health Problems (ICD) is an international diagnostic tool for health management, epidemiology, and clinical purposes. The list of ICD codes changes over time.

Its most up-to-date version, first released in 1992, is ICD-10, which is an upgrade from the previous one – ICD-9 and includes more codes and classifications for updated conditions and diagnoses than its predecessor. ICD-10 contains over 70,000 disease codes. 

The 11th revision will officially come into effect on January 1, 2022, after every WHO member endorsed it at the organization’s 72nd World Health Assembly (WHA) on May 25, 2019. In between revisions, the ICD manual goes through annual minor updates and triennial major updates.

Although WHO is the manager and publisher of the base ICD, some of its member states have modified it in accordance with their specific needs. Currently, the US is using two types of ICD-10 systems (both updated annually):

  • ICD-10-CM (Clinical Modification), which includes diagnosis codes
  • ICD-10-PCS (Procedure Coding System), which includes procedure codes

ICD codes can have between three to seven alphanumeric characters and classify a wide array of symptoms, signs, complaints, abnormal findings, social circumstances, as well as external causes of disease or injury. Hence, larger categories include similar diseases.

The first three characters in the code mark the category and can stand alone if the category has no further subdivision. The first alpha letter groups diseases together to specify a specific condition, organ system, or a condition characteristic. 

For example, ‘A’ is for ‘Infectious and parasitic diseases’, ‘G’ for ‘Nervous system’, ‘Q’ for ‘Congenital and chromosomal abnormalities’, and ‘Z’ for ‘Factors influencing health status and contact with health services’.

The next three characters refer to the related etiology, severity, anatomic location, or another important clinical detail. Appearing only rarely, the seventh character is the extension that provides information about the characteristic of the encounter. 

For injuries, these character extensions include: initial encounter – ‘A’, subsequent encounter – ‘D’, and sequela – ‘S’. It always stands in seventh place. Hence, if a code has fewer than six characters, the fields before the extension need to contain a placeholder X.

The most common ICD codes for family practice

Some ICD-10 codes appear more often than others in family practice, such as:

  • Z00.00 – General adult medical examination without abnormal findings
  • Z12.4 – Screening for malignant neoplasm of cervix
  • Z12.5 – Screening for malignant neoplasm of prostate
  • Z79.01 – Long-term (current) use of anticoagulants
  • Z79.891 – Long-term (current) use of opiate analgesic
  • Z01.411 Gynecological exam (general, routine) with abnormal findings
  • Z01.419 Gynecological exam (general, routine) without abnormal findings
  • Z34.80 – Supervision of normal pregnancy, unspecified trimester
  • I10 – Essential (primary) hypertension
  • I48.91 – Unspecified atrial fibrillation
  • J02.9 – Acute pharyngitis, unspecified
  • E11.9 – Type 2 diabetes mellitus without complications
  • E11.65 – Type 2 diabetes mellitus with hyperglycemia
  • G93.3 – Postviral fatigue syndrome
  • R10.84 – Generalized abdominal pain
  • R63.5 – Abnormal weight gain
  • R51 – Headache
  • R50.9 – Fever, unspecified
  • R53.1 – Weakness
  • R31.9 – Hematuria
  • R19.7 – Diarrhea, unspecified
  • K52.2 – Allergic and dietetic gastroenteritis and colitis
  • R30.0 – Dysuria
  • R30.9 – Painful micturition, unspecified
  • R79.0 – Abnormal level of blood mineral
  • R60.0 – Localized edema
  • R60.1 – Generalized edema
  • R05 – Cough
  • R42 – Dizziness and giddiness
  • N39.0 – Urinary tract infection, site not specified
  • N30.00 – Acute cystitis without hematuria
  • N30.01 – Acute cystitis with hematuria
  • E78.5 – Hyperlipidemia, unspecified
  • E78.2 – Mixed hyperlipidemia
  • E78.0 – Pure hypocholesterolemia
  • E55.9 – Vitamin D deficiency, unspecified
  • E03.9 – Hypothyroidism, unspecified
  • D64.9 – Anemia, unspecified
  • D50.9  – Iron deficiency anemia, unspecified
  • L03.90 – Cellulitis, unspecified
  • L03.91 – Acute lymphangitis, unspecified

The most common ICD codes for mental disorders

Practitioners treating mental disorders will commonly encounter these ICD-10 codes:

  • Part F40-48 – Anxiety, dissociative, stress-related, somatoform and other nonpsychotic mental disorders, for example:
  • F40.01 – Agoraphobia with panic disorder
  • F40.11 – Social phobia, generalized
  • F40.9 – Phobic anxiety disorder, unspecified
  • F41.1 – Generalized anxiety disorder
  • F41.9 – Anxiety disorder, unspecified
  • F42 – Obsessive-compulsive disorder
  • F43.10 – Post-traumatic stress disorder, unspecified
  • F43.20 – Adjustment disorder, unspecified
  • F43.21 – Adjustment disorder with depressed mood
  • F44.4 – Conversion disorder with motor symptom or deficit
  • F44.9 – Dissociative and conversion disorder, unspecified
  • Part F60-F69 – Disorders of adult personality and behavior, including:
  • F60.3 – Borderline personality disorder
  • F64.2 – Gender identity disorder of childhood
  • Part F50-F59 – Behavioral syndromes associated with psychological disturbances and physical factors:
  • F50.00 – Anorexia nervosa, unspecified
  • F50.2 – Bulimia nervosa
  • F51.01 – Primary insomnia
  • F51.03 – Paradoxical insomnia
  • F51.04 – Psychophysiologic insomnia
  • F51.05 – Insomnia due to other mental disorder
  • F51.09 – Other insomnia not due to a substance or known physiological condition
  • Part F80-F89 – Pervasive and specific developmental disorders, most often:
  • F84.0 – Autistic disorder
  • F84.2 – Rett’s syndrome
  • F84.5 – Asperger’s syndrome
  • Part F30-F39 – Mood [affective] disorders, like:
  • F31.0 – Bipolar disorder, current episode hypomanic
  • F31.10 – Bipolar disorder, current episode manic without psychotic features, unspecified
  • F31.5 – Bipolar disorder, current episode depressed, severe, with psychotic features
  • F31.60 – Bipolar disorder, current episode mixed, unspecified
  • F31.70 – Bipolar disorder, currently in remission, most recent episode unspecified
  • F31.81 – Bipolar II disorder
  • F31.9 – Bipolar disorder, unspecified
  • F32.1 – Major depressive disorder, single episode, severe without psychotic features
  • F33.1 – Major depressive disorder, recurrent, moderate
  • F34.1 – Dysthymic disorder
  • F39 – Unspecified mood [affective] disorder
  • Part F20-F29 – Schizophrenia, schizotypal, delusional, and other non-mood psychotic disorders, such as:
  • F20.9 – Schizophrenia, unspecified
  • F25.1 – Schizoaffective disorder, depressive type
  • F25.9 – Schizoaffective disorder, unspecified
  • Part F90-F98 – Behavioral and emotional disorders with onset usually occurring in childhood and adolescence. Examples include:
  • F90.0  – Attention-deficit hyperactivity disorder, predominantly inattentive type
  • F90.1 – Attention-deficit hyperactivity disorder, predominantly hyperactive type
  • F90.9 – Attention-deficit hyperactivity disorder, unspecified type
  • Part F10-F19 – Mental and behavioral disorders due to psychoactive substance use:
  • F10.27 – Alcohol dependence with alcohol-induced persisting dementia
  • F11.20 – Opioid dependence, uncomplicated
  • F11.221 – Opioid dependence with intoxication delirium
  • F11.23 – Opioid dependence with withdrawal
  • F13.26 – Sedative, hypnotic or anxiolytic dependence with sedative, hypnotic, or anxiolytic-induced persisting amnestic disorder
  • Part F01-F09 – Mental disorders due to known psychological conditions:
  • F02.80 – Dementia in other diseases classified elsewhere without behavioral disturbance
  • F03.90 – Unspecified dementia without behavioral disturbance
  • F05 – Delirium due to known physiological condition
  • F06.32 – Mood disorder due to known physiological condition with major depressive-like episode
  • Part G30-G32 (within Chapter 6 – Diseases of the nervous system) – Other generative diseases of the nervous system, such as:
  • G30.0 – Alzheimer’s disease with early onset
  • G30.1 – Alzheimer’s disease with late onset
  • G30.9 – Alzheimer’s disease, unspecified

For the full list of ICD codes, click here.