Daggers, asterisks and other footnotes for ICD-11

Sometimes, coding guidelines dictate that an illness be reported using multiple diagnosis codes. A widely used instance of this is for a condition that needs both the etiology of the disease (the underlying problem or cause) and one of its manifestations (the secondary condition caused by the problem). In the World Health Organization’s (WHO) release of ICD-9 and ICD-10, the answer is to use the “dagger and asterisk” system. While the United States has instead handled this by incorporating some pre-coordination in the clinical modification of ICD-10-CM, other countries like, Australia, Canada and Germany, have retained this system in their ICD-10-AM, ICD-CA and ICD-GM, respectively.

Codes for etiology are annotated by a dagger symbol (†), and manifestation codes by an asterisk symbol (*). Let’s look at an example to show this with Tuberculosis of the knee - it is assigned a combination of A18.0† M01.16*.

A18.0†  Tuberculosis of bones and joints

Tuberculosis of:

• hip (M01.15*)
• knee (M01.16*)
• vertebral column (M49.0-*)

Tuberculous:

• arthritis (M01.1-*)
• mastoiditis (H75.0*)
• necrosis of bone (M90.0-*)
• osteitis (M90.0-*)
• osteomyelitis (M90.0-*)
• synovitis (M68.0-*)
• tenosynovitis (M68.0-*)

It’s also important to note that there are coding guidelines on the ordering of these combination codes, including that there are full and part time dagger asterisk codes. Full-time means that they must always be assigned together. Part time means that only in certain cases are they assigned together. 

Dagger codes are classified according to etiology. They are primary codes, meaning they can be, but do not have to be, combined with an asterisk code although they frequently are. Apart from codes marked as dagger codes, each random primary code can be used as an etiology code and combined with an asterisk code. In this case, the encoder marks the etiology code with a dagger.

Asterisk codes designate the manifestation of a disease. As additional codes, they must never be used on their own but only as part of a dual encoding in the "dagger and asterisk" system, i.e., always in conjunction with a dagger code or another primary code. Very often, the corresponding dagger code is given for an asterisk code.

Additionally, there are sets of codes to be used to add more detail (e.g., B95-B97) or lists of sub-classifications to add anatomical detail to categories.

The dagger and asterisk system is a precursor to ICD-11’s concept of post-coordination and has been removed in ICD-11. The functionality of coding etiology and manifestation remains, as does the need for additional clinical details like laterality, severity, related complications, location, substances and the like. Post-coordination, or cluster coding, and the use of stem codes with extension codes provide limitless opportunity for specificity.

The ICD-11 equivalents of asterisk codes (i.e., codes for manifestations) and other codes that served to add detail may be found in Chapter 21, “Symptoms, signs or clinical findings, not elsewhere classified.” Lists for coding-optional anatomical detail have been grouped into one section in Chapter X, “Extension codes.” A portion of former asterisk codes also reside in the corresponding body system chapter. Asterisk codes that were repetitions of the dagger code were removed.

Our earlier ICD-10-AM example of Tuberculous arthritis of the knee joint will be 1B12.40/FA10.0 in ICD-11. So, put your daggers† and asterisks* aside, the future is full of ampersands (&) and forward slashes (/).

Michelle Badore is a global clinical and nosology content manager at 3M Health Information Systems.