Each hospital admission is assigned a main diagnosis (cause) of admission, and each death is assigned an underlying cause of death. Secondary diagnosis codes and causes can also be given if there are other influential medical factors or causes for the admission or death. The system used to code these diagnoses and causes is the International Classification of Diseases. The latest version used for hospital and mortality records is version 10 which was introduced in 2001. This not only consists of codes for all the known medical conditions and diseases, but also other reasons, causes or factors for the admission or death. These other codes include codes for routine hospital care, such as those related to screening, diagnosis or maternity, and other external factors such as traffic accidents, injuries, falls, poisoning, suicide, etc. It is possible that not all relevant secondary diagnoses codes will be coded, and included on the admission or mortality data as it will depend on what doctors write and record in their medical notes or on the death certificate.
Each of the ICD codes have been assigned an ‘alcohol attributable fraction’ (AAF) which has been determined through research and analysis of hospital admission and death data nationally. It is not based on ‘real’ data (with the exception of alcohol-specific conditions), and only represents a modelled estimate of the numbers and rates of alcohol-related admissions and deaths. The assigned AAF values ranges from zero to one. The AAF are based on quite rigorous research, so are probably quite accurate, but the estimated number and percentages of alcohol-related admissions and deaths can differ substantially depending on whether all secondary diagnoses codes are used in calculating the AAF for a specific admission or death, or just some secondary diagnoses codes such as those relating to external sources. The AAF values are often the same for medical conditions and diseases regardless of whether they are assigned to a hospital admission or a death, although there are some exceptions such as for stroke, oesophageal varices and unspecified liver disease. The values of AAF assigned to external causes do usually differ depending on whether hospital admissions or deaths are being examined. The same methodology and calculations apply as to how the AAFs are applied to admissions or deaths. Different AAF values are assigned on the basis of the diagnosis codes for different age groups, and the value of the AAF often differ between males and females. AAF values are generally not assigned to those aged 0-15 years. It is relatively easy (and accurate) to assign an AAF to conditions that are entirely due to alcohol such as alcoholic liver disease and ethanol poisoning as they are assigned an AAF of 1 (wholly attributable to alcohol or alcohol-specific). Some conditions will be assigned a value of zero as there is no current evidence that they are alcohol-related at all. Virtually all admissions (and deaths) among children and young people are assigned a value of zero. Other specific conditions where there is evidence that alcohol is (sometimes) involved or is or can be a contributing factor will be assigned an AAF value between zero and one. There are a small number of medical conditions and diseases where the value assigned to the AAF is negative denoting a protective effect (such as diabetes and ischaemic heart disease).
Examples of AAF values
Mental and behavioural disorders due to the use of alcohol – AAF = 1
Alcoholic liver disease – AAF = 1
Ethanol poisoning – AAF = 1
Colorectal cancer among men aged 55-64 years – AAF = 0.16 (denoting around 16% of the disease is attributable to alcohol)
Breast cancer among women aged 45-54 years – AAF = 0.17 (denoting around 17% of the disease is attributable to alcohol)
Epilepsy men among aged 25-34 years – AAF = 0.25 (denoting around 25% of the disease is attributable to alcohol)
Ischaemic heart disease among men aged 25-34 years – AAF = -0.18 (protective effect)
Hypertensive disease among men aged 55-64 years – AAF = 0.17 (denoting around 17% of the disease is attributable to alcohol)
Road / pedestrian traffic accidents (morbidity) among men aged 25-34 years – AAF = 0.15 (denoting around 15% of the admissions are attributable to alcohol)
Road / pedestrian traffic accidents (mortality) among men aged 55-64 years – AAF = 0.38 (denoting around 38% of the deaths are attributable to alcohol)
Road / pedestrian traffic accidents (morbidity) among men aged 55-64 years – AAF = 0.25 (denoting around 25% of the admissions are attributable to alcohol)
Self-harm or event of undermined intent (mortality) among men aged 35-44 years – AAF = 0.17 (denoting around 17% of the deaths are attributable to alcohol)
Self-harm or event of undermined intent (morbidity) among men aged 35-44 years – AAF = 0.07 (denoting around 7% of the admissions are attributable to alcohol)
There are different measures used to define alcohol-specific and alcohol-related admissions or deaths. In all cases, the AAF of the primary diagnosis of the admission or the underlying cause of the death are used in the calculation (in most cases it will be zero so not contribute to the total number of alcohol admissions or deaths), but depending on the different measures, then AAF value for none, some or all of the secondary diagnosis codes of the admission / death are used in the calculation.
The Office for Health Improvement & Disparities’ Local Alcohol Profiles use these AAFs to estimate the number of hospital admissions (and deaths) for each local authority that are alcohol-specific or alcohol-related. There are three methods of calculating alcohol admissions within the Alcohol Profiles: (i) alcohol-specific admissions where the primary diagnosis or any of the secondary diagnoses relate to an alcohol-specific condition or where the condition is wholly due to alcohol such as alcoholic liver disease or ethanol poisoning (where the AAF is one); (ii) alcohol-related “narrow measure” where the maximum AAF is assigned to the admission based on the AAF assigned to the primary diagnosis admission code and AAFs assigned to only secondary diagnoses codes that are due to an external cause such as a road traffic accident, intentional self-harm, fire, assault, fall, etc.; and (iii) alcohol-related admissions “broad measure” where individual admissions are assigned an AAF based on the maximum of the AAFs across all primary diagnosis and secondary diagnosis codes.
There are two methods of calculating deaths attributable to alcohol within the Alcohol Profiles: (i) alcohol-specific deaths where the death is wholly attributable to alcohol (where the AAF is one); and (ii) alcohol-related deaths which is based on the AAF values for the underlying cause of death, but also includes any deaths where any of the secondary cause of the death are ethanol poisoning, methanol poisoning or toxic effects of alcohol.
Once each admission or death is assigned an AAF (maximum of AAFs over the primary diagnosis and considered secondary diagnoses codes), then the AAF values are summed over all admissions or all deaths to give a total number of alcohol admissions or deaths (within a specified time period). The AAF values can be summed for each age group and separately, and then a directly standardised admission or mortality rate (age-standardised rate) can then be calculated.
For instance, if an admission for a man aged 55-64 years had a primary diagnosis of colorectal cancer and a secondary diagnosis code of hypertensive disease, then the AAF values would be 0.16 and 0.17 respectively. When using the broad measure for hospital admissions, an AAF value of 0.17 (the maximum) would be assigned for this admission, whereas if the narrow measure for hospital admission was used then an AAF value of 0.16 would be used (only considering the primary diagnosis and not the secondary diagnosis as it is not an external cause).
For instance, if an admission for a man aged 25-34 years had a primary diagnosis of a fracture of the leg, and secondary diagnoses for a road traffic accident and epilepsy then the AAF values would be 0, 0.15 and 0.25 respectively. When using the broad measure for hospital admissions, an AAF value of 0.25 (maximum when epilepsy was included) would be assigned for this admission, but using the narrow measure for hospital admissions, an AAF value of 0.15 (maximum when epilepsy was not included) would be assigned to this admission as it would include only the secondary diagnosis relating to the external cause of a road traffic accident.
For instance, if there were three admissions one for alcoholic liver disease, another for a man aged 55-64 years with colorectal cancer and hypertensive disease, and another man aged 25-34 years with a fractured leg and epilepsy who had been in a car accident, then the number of alcohol admissions based on the broad measure would be 1.42 (summing 1, 0.17, and 0.25) and the number of alcohol admissions based on the narrow measure would be 1.31 (summing 1, 0.16 and 0.15). The hospital admission rate could then be calculated by dividing by the population, although in practice, it is usual that directly standardised rates are produced.
Also see Alcohol-attributable fractions for England: an update, published by Public Health England (now Office for Health Improvement & Disparities) in 2020.
Also see Alcohol Consumption – Definitions and Units, International Classification of Diseases and Smoking Attributable Fractions.
Also see Directly Standardised Rate.