Comorbid Diagnosis

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For other diagnoses we collect see Admit Diagnosis or Acquired Diagnosis / Complication.

Comorbid Diagnoses are for diseases the patient has had for some time. Comorbidities can be a factor in increasing the patient risk of dying; see Charlson Comorbidity Index. A Comorbid Diagnosis is coded by setting the Dx_Type to "comorbid".

Collection Instructions

When to code a Comorbid Diagnosis

  • Either:
    • Dx is chronic and was present and known prior to admission, even if it was only discovered during this admission
    • Dx is in the past and is resolved and is included in one of the: Category: Past medical history codes
    • Dx is chronic and was not known prior to admission

When to use Comorbid Diagnosis vs Admit Diagnosis or neither

When not to code a dx at all

  • Dx was present in the past but that problem is resolved AND does not fit into one of the Category: Past medical history codes
  • Do not code diagnoses that occur during this admission as a comorbid diagnoses. If they have completely resolved then do not code as a comorbid diagnosis until the next admission if applicable. ie. surgical ward had a COVID pneumonia resolved prior to ICU admission. Do not code Past history of Covid-19 infection until the next hospital admission.

Regular comorbid rules exception: Strokes (of any sort, ischemic or hemorrhagic) -- code even resolved strokes with no current sequelae as comorbid diagnoses. If a patient has a past history of stroke, use the regular stroke codes to identify this, even if the patient does not have any residual deficits we will now capture ANY past history of stroke. This is contrary to the usual rules about Comorbid_Diagnosis#When_not_to_code_a_dx_at_all.

  • Patient had the left lung removed 7 years ago. Dont code the removal of the lung CCI, but instead code Past history, removal of all or part of lung
  • For someone who had a Cardiac arrest in the past, don't code that as a Comorbid Diagnosis in future admissions, but instead DO code the cause of the cardiac arrest, e.g. an arrythmia, or coronary artery disease, etc.
  • Patient has hypertension for which she takes medications and it is well controlled, but not related to the reasons for admission. Code this, because even if not part of the reason for the current admission, the hypertension IS relevant to this person's chronic medical situation and thus SHOULD be coded, as a Comorbid Diagnosis.
  • Patient had ARDS (noncardiogenic pulmonary edema) a few years ago, and while ARDS is only an acute problem and thus is no longer active, his lungs never fully recovered and he has Respiratory failure (insufficiency), chronic which should be coded as a Comorbid Diagnosis.
  • Chronic and ongoing old conditions should be coded -- as a Comorbid Diagnosis if not part of the reason for this admission.

Some diagnoses can/should be coded as BOTH Admit Diagnosis and Comorbid Diagnosis

If a dx is chronic but also actively treated during this admission, code it as both Admit Diagnosis and Comorbid Diagnosis.

  • ex1: Patient who has been, and still is, being treated for active pulmonary TB as an outpatient, and is admitted for an acute MI. Here since on the current admission the TB is still being actively treated, it qualifies as an Admit Diagnosis, as above. But because it has been present from long before this admission, it also qualifies as an "active" Comorbid Diagnosis.
  • ex2: Patient has a past history of CHF and thus it should be coded as a Comorbid Diagnosis. And if the CHF is worse at admission and it is part of the reason for admission, then CHF should also be an Admit Diagnosis.

Recurrent conditions

  • Do not code a recurrent condition that is NOT currently present -- if currently active, include as Admit Diagnosis, otherwise don't code it
  • Ex1: Recurrent pneumonia -- in between the infections, there IS NO pneumonia
  • Do code conditions that by nature have intermittent rather than continuous symptoms, but where the underlying condition doesn't go away.

Past medical history

Past medical history codes

Past medical history codes should only be captured as Comorbid Diagnoses that represent previous procedures or medical situations. Their names usually follow the pattern "Past history of X" or "X, has one". See Category:Past medical history for a list.

Past medical history codes:

Controlling Dx Type for ICD10 codes

This wiki page talks about which ICD10 codes are allowed to be Comorbid Diagnosis vs. Admit Diagnosis vs. Acquired Diagnosis Dx Type. See Controlling Dx Type for ICD10 codes for a discussion about cross-checks for these.

Legacy - did not use to code Comorbid Diagnoses only discovered during this admission

see how this used to be coded...   
  • As of June 25, 2020, the rules were revised for coding as Comorbid Diagnoses those diagnosed during the current hospitalization (either at admission or thereafter) but which virtually certainly were present pre-admission.

signs and symptoms should not be code as comorbidities

  • Signs, symptoms and findings (e.g. chest pain or dyspnea, or abnormal LFTs) should NOT be coded as comorbidities. Only real specific diagnoses should.

Patient has no comorbidities

If a patient has no comorbidities, enter No Comorbidities (ICD10 code).


You will need to enter priorities for comorbids. For comorbids the priorities will only be used for grouping Combined ICD10 codes, not for prioritizing them in any order of importance.

Transfer of Comorbids on transfer between wards

See Patient copier button for more.

Data Integrity Checks (automatic list)

Controlling Dx Type for ICD10 codesCCMDB.accdbdeclined
Query check ICD10 duplicatesCCMDB.accdbdeclined
Query check ICD10 dateCCMDB.accdbimplemented
Query check ICD10 Comorbids NoComo code but othersCCMDB.accdbimplemented

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