Diagnosis coding

The illnesses, diseases and injuries suffered by hospital patients are currently recorded using the International Classification of Diseases, Tenth Revision (ICD-10), published by the World Health Organization (WHO).

Information about a patient's diagnosis, recorded in their notes by the clinician treating them, is translated into ICD-10 codes by a clinical coder. This means it is possible to select and compare conditions consistently, not only in HES but also across the world wherever ICD-10 is used.

This brief overview of the classification may help you navigate our free diagnosis tables.

What are ICD-10 codes?

ICD-10 codes consist of a single letter followed by three or more digits, with a decimal point between the second and third (eg K35.1: Acute Appendicitis with peritoneal abscess). As there are many thousands of variations at the 4-character level (where all three digits are used) it is common practice to summarise at the 3-character level (eg K35: Acute appendicitis, which includes peritoneal abscess and all other forms of the condition).

There are diagnosis tables available for download at the 3-character level and the more detailed 4-character level. The diagnoses are presented in code order rather than by diagnosis name.

What do we mean by 'primary' and 'secondary' diagnoses?

The primary diagnosis is defined as the main condition treated or investigated during the relevant episode of healthcare (where a definitive diagnosis cannot be given, a code describing the main symptom, abnormal finding or problem should be used).

The HES Data Warehouse also stores up to thirteen additional, secondary diagnoses (six prior to 2002-03), which describe other conditions the patient may have. For example, when treating someone for heart disease it would be important to record that they also had diabetes as, although that isn't the main reason for the current period of care, it is an important factor in managing the heart condition.

The hospital will enter only the number of codes necessary to describe the patient's condition - most records have far fewer than fourteen.

Using ICD-10 to classify diagnoses

ICD-10 is broken down into a series of chapters of related conditions. The list of chapters below should help you locate the particular diagnosis you are interested in:

• A and B - Certain infectious and parasitic diseases
• C00 to D48 - Neoplasms
• D50 to D89 - Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism
• E - Endocrine, nutritional and metabolic diseases
• F - Mental and behavioural disorders
• G - Diseases of the nervous system
• H00 to H59 - Diseases of the eye and adnexa
• H60 to H95 - Diseases of the ear and mastoid process
• I - Diseases of the circulatory system
• J - Diseases of the respiratory system
• K - Diseases of the digestive system
• L - Diseases of the skin and subcutaneous tissue
• M - Diseases of the musculoskeletal system and connective tissue
• N - Diseases of the 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 laboratory findings, not elsewhere classified
• S and T - Injury, poisoning and certain other consequences of external causes
• U - This letter is currently left vacant
• V, W, X and Y - External causes of morbidity and mortality
• Z - Factors influencing health status and contact with health services

Note: Codes in the range V01 to Y98 are never used as a primary diagnosis. These codes are intended to support the primary diagnosis (normally a code beginning S or T) by giving information about the cause of injuries and poisonings (eg V37 indicates 'Occupant of three-wheeled motor vehicle injured in collision with fixed or stationary object').