Description

This is a list of codes for diabetes: type 1, type 2 and unspecified type. It does not include codes for other types of diabetes e.g. gestational, secondary, monogenic, syndromic.

Rules

  • Check to make sure the date is within the range expected given the data source and patient DOB and death dates.

  • Presence of one of these codes may not be sufficient to define diabetes cases. In primary care data, the presence of a diabetes Quality and Outcome Framework (QOF) code is more specific for true diabetes cases ('qof' column in our SNOMED codelist indicates whether a code is a diabetes QOF code or not). In addition, specificity can be increased by removing patients with codes for other types of diabetes mellitus (gestational, secondary etc.) or diabetes insipidus, who may erroneously have diabetes mellitus codes in their records.

  • Our algorithm for defining diabetes diagnosis date: the earliest of a code for diabetes, an HbA1c>=48 mmol/mol (see investigation/HbA1c) or a prescription for a glucose-lowering medication (including insulin; see medications/diabetes). It may not be possible to determine diagnosis dates in some datasets if historical data is not available. For those with type 2 diabetes, diabetes codes within the year of birth are ignored. It may be possible to ignore other diabetes codes which clearly do not relate to diagnosis in some datasets e.g. in CPRD ignore diabetes codes with obstype=4 as these represent family history.

  • Our algorithm for distinguishing between type 1 and type 2 diabetes:

  • No insulin prescriptions: Type 2

  • With at least one insulin prescription:

    • At least one Type 1 and no Type 2 codes: Type 1
    • At least one Type 2 and no Type 1 codes: Type 2
    • Mix of Type 1 and Type 2 codes: if number of Type 1 medcodes >=2 x number of Type 2 medcodes, Type 1, otherwise Type 2
    • No Type 1 or Type 2 codes: leave as 'unclassified'. If required, a probable diabetes type can be assigned as follows: where time to insulin from diagnosis available: if diagnosed <35 years of age and on insulin within 1 year of diagnosis, Type 1, otherwise Type 2; if time to insulin not available: if diagnosed <35 years and not currently taking a non-insulin glucose-lowering medication (no prescription for a non-insulin glucose-lowering medication within 6 months, Type 1, otherwise Type 2.

  • Since diabetes type is used to inform whether diabetes codes in year of birth should be excluded or not, this can create a circular problem in those with no type 1 or type 2-specific codes, where someone is classified as type 1 if diabetes codes in year of birth are included, and type 2 if diabetes medcodes in year of birth are excluded (or vice versa, if time to insulin from diagnosis is affected). These people are classed as 'unclassified', and need further investigation to establish diabetes type and date/age of diagnosis.

Origins

  • The origin of the SNOMED codelist was searching for diabetes and related codes in the SNOMED CT UK edition release 41.2.0 from NHS TRUD.

Versions

  • The SNOMED codelist was updated on 23/02/2026 to remove 9 codes for specific non-type 1/non-type 2 diabetes types, and reclassify two type 1 codes to type 2.

Data