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


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.


Como Admit Acquired Primary Limits - this is part of that discussion - if we limit which admits will count as comos we need to review

  • SMW

  • Cargo

  • Categories

When to use Comorbid 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 is not one of the Category: Past medical history codes
    • including earlier on during a long admission
  • Patient had appendix removed 7 years ago and is now admitted with injuries from a car accident; don't code the appendix removal at all.
  • Patient had the left lung removed 7 years ago. Code this because it is relevant to his medical status because the guy only has 1 lung now. Similar if he had his spleen removed in the past.
  • Patient has hypertension that's well controlled and not at all an issue related to the reasons for admission. Code this, because even if not relevant to current admission the hypertension IS relevant to this person's chronic medical situation and thus SHOULD be coded, as a comorbid.
  • pneumonia recurrent, of course should be coded in admit or acquired but it-should NOT be coded as a comorbid.

When to code an Admit Diagnosis

  • Dx was present prior to physical arrival in their bed on unit/ward
  • Dx is relevant to this admission in that it is either: (a) an acute or exacerbated condition (as opposed to a chronic, stable condition -- e.g. stable diabetes), OR (b) it is a condition that is incidental to the reason(s) for admission and is still receiving "acute" treatment.
  • Example of 'a':
  • Patient admitted with a CAP to ICU who was intubated, ventilated and placed on antibiotics. They develop Atrial fibrillation and/or atrial flutter and are placed on meds which may need adjusting because they are still having breakthrough rapid Afib. Once extubated they are often ready for the medicine ward but are still on antibiotics for their CAP and require watching to see if their Afib returns. The medicine collector would list both CAP and Afib as part of their admitting diagnoses.
  • Patient with BPH who is not on any medications for it. They still have BPH but it is not an active problem being treated and so would be a Comorbid Diagnosis
  • Patient with diabetes admitted for an leg fracture. Here the diabetes is stable and (of course) treated during admission, but should be coded as a Comorbid Diagnosis.
  • Example of 'b':
  • Tuberculosis is an admit diagnosis in a person admitted with an acute MI, but still getting the 9 months of treatment for active tuberculosis.
  • Example of NOT an Admit Diagnosis:
  • Past h/o A-fib that's present but stable and getting the same treatment it has been for awhile. This is just a Comorbid Diagnosis

When to code a Comorbid Diagnosis

  • Dx does not qualify as an Admit Diagnosis and is chronic and was present prior to admission
    • Code these even if the diagnosis of the condition was only made during the current hospital admission but it is quite clear that it must have existed before admission (even if that wasn't known). Here are some examples of that situation:
  • If a patient is admitted with pneumonia and on further workup is found to have CA of the lung, then this is coded in comorbid as it is obvious that the cancer must have been there for a while prior to admission.
  • Patient comes in with abdominal pain. Diagnosed as gastroenteritis but incidentally pt is found to be HIV +ve. You would code HIV +ve as a comorbid. Again, this is obvious that the pt had this problem for a while prior to admission to the hospital.
Recurrent conditions
  • Do not code recurrent acute conditions that resolve between recurrences; for these, if currently active, include as Admit Diagnosis, otherwise don't code them.
  • Recurrent pneumonia -- although one can be left with chronic sequelae of pneumonia (e.g. a pneumatocele or a region of emphysema or a bulla), in between these infections, there IS NO pneumonia
  • Recurrent severe sepsis -- same as above
  • Do code conditions that by nature have intermittent rather than continuous symptoms, but where the underlying condition doesn't go away.
  • So, for chronic conditions that are at their baseline at admission, code those as Comorbid Diagnosis -- e.g. COPD.
    • This "baseline" could include either of: not currently getting any treatment; getting maintenance/control treatment.
    • Obviously, if the chronic condition (e.g. COPD) is in exacerbation at admission, then it should be coded as Admit Diagnosis -- e.g COPD, acute exacerbation
Past medical history

Category:Past medical history contains codes that should only be captured as Comorbid Diagnosis that represent previous procedures or medical situations that can't be captured in another way. Their names usually follow the pattern "Past history of X" or "Artifical opening, has one".

Past medical history codes:

When a diagnosis can be coded as BOTH a comorbid and either acute or acquired

  • This may occur
*Patient has a past history of CHF and thus it should be coded as a comorbid.  And if the CHF is worse at admission and it is part of the reason for admission, then CHF should also be an admit code too.  If instead, CHF is stable at admit, but worsens after admit, then the CHF could be an acute/acquired diagnosis

Controlling Dx Type for ICD10 codes

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

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).

Transfer of Comorbids on transfer between wards

There has been repeated talk about facilitating the collection of comorbids between collectors for different patient ward stays. Specifically, we have talked about a Patient copier button but decided not to implement it. See Patient copier button for more.

Data Integrity Checks (SMW)

Query check ICD10 dateCCMDB.mdbimplemented
Query check ICD10 Comorbids NoComo code but othersCCMDB.mdbimplemented

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