ICD-11 Cluster coding (post-coordination) for morbidity

A significant new feature within ICD–11 is the clustering (or linking) function of related diagnostic concepts to better capture the clinical picture of an episode of care. Clustering (post-coordination) in ICD-11 has allowed for the introduction of new clinical coding mechanisms for capturing clinical information in dimensions such as:

  • quality and safety coding for healthcare related injury and harm
  • the addition of clinical detail using extension codes
  • the specification of diagnosis type and diagnosis timing using extension codes
  • the comprehensive description of late effects (sequelae) arising from prior conditions
  • the description of inter related stem code diagnoses where there is a clear causal relationship

The post-coordinated coding of conditions uses the backslash (‘/’) as a separator within a cluster. For those countries also wishing to capture further specificity through the use of extension codes, the ampersand (‘&’) may also be used to separate a condition with an extension code.
Cluster coding is demonstrated in the following examples.

Example 1:
A patient is admitted to hospital for laser treatment of their diabetic retinopathy due to Type 2 diabetes mellitus. During the admission the patient’s medication for arterial hypertension required adjustment on a number of occasions before discharge.

Cluster 1: Code as main condition the diabetic retinopathy, unspecified followed by Type 2 diabetes mellitus 9B71.0Z/5A11
Cluster 2: Code the essential hypertension BA00.Z
For morbidity coding, the order of the codes in the first cluster in Example 1 has the diabetic retinopathy sequenced first as this is the main condition followed by the associated condition for Type 2 diabetes.
As indicated in Example 2 below, in countries where extension codes are used, it would also be acceptable for a coder to sequence the Type 2 diabetes mellitus as the underlying cause (aetiology) of the diabetic retinopathy first in the cluster as long as the extension code for ‘main condition’ is included with the diabetic retinopathy.

Example 2:
A patient is admitted to hospital for laser treatment of their diabetic retinopathy due to Type 2 diabetes mellitus. During the admission the patient’s medication for arterial hypertension required adjustment on a number of occasions before discharge.

Cluster 1: Type 2 diabetes mellitus followed by diabetic retinopathy, unspecified, followed by extension code for main condition 5A11/9B71.0Z&XY0Y
Examples 1 and 2 above show two conditions which have an established causal link (i.e. diabetic retinopathy due to Type 2 diabetes mellitus). Where an established causal link is not documented or cannot be inferred, the two conditions cannot be part of the same cluster.
Example 3 below demonstrates cluster coding where a causal link between the cataract and the Type 2 diabetes has not been documented and cannot be inferred. Note the extension code following the code for the cataract indicates laterality, in this instance it was a right cataract.

Example 3:
Patient admitted for right cataract extraction. The patient also has Type 2 diabetes mellitus and was reviewed by the endocrinologist and dietitian for their long term diet and insulin plan.

Cluster 1: Cataract, unspecified, right 9B10.Z&XK9K
Cluster 2: Type 2 diabetes mellitus 5A11
Example 4 below demonstrates how cluster coding can be used for the purposes of quality and patient safety.

Example 4
A 63 year old man had a left knee-replacement less than a year ago, because of arthritis. The implanted device has come loose, resulting in pain and reduced function.

Harm Pain in joint ME82; Specific Anatomy: Knee joint XA8RL1; Laterality: Left XK8G
Cause Orthopaedic devices associated with adverse incidents, prosthetic or other implants, materials or accessory devices PK99.2
Mode Dislodgement, misconnection or de-attachment, as mode of injury or harm PL12.4
Cluster ME82&XA8RL1&XK8G/PK99.2/PL12.4

For more information and further examples on post-coordination using ICD-11, please refer to the ICD-11 Reference Guide available at: https://icd.who.int/browse11/content/refguide.ICD11_en/html/index.html