Underdosing: A New Concept in ICD-10-CM

Coding and BillingNo Comments

medication instructionsThe implementation of ICD-10-CM will bring with it many changes in the way we code common diagnoses. Along with those changes, ICD-10-CM will also introduce new concepts in coding that are designed to report circumstances that are not currently captured by the ICD-9-CM code classification. One of these important new concepts is underdosing.

Underdosing occurs when a patient takes less of a medication than is prescribed by the provider or the manufacturer’s instructions. Underdosing often leads to a relapse or exacerbation of the patient’s condition. For example, if a diabetic patient does not take enough insulin they may end up at the emergency room with blurred vision, fatigue, and headache due to hyperglycemia.

Having codes to report underdosing situations is important as a decline in a patient’s condition can raise quality of care issues, which can additionally have an impact on reimbursement. The ability to report underdosing helps clarify that the patient’s current state of relapse or exacerbation is not due to the fact that the provider did not prescribe a viable course of treatment—but rather that the patient did not follow the prescribed treatment plan.

Underdosing situations are reported with codes from the Poisoning by, Adverse Effects of, and Underdosing of Drugs, Medicaments, and Biological Substances (T36-T50) category of ICD-10-CM codes. Underdosing situations are differentiated from poisonings and adverse effects by the assignment of a fifth or sixth character of “6”.

Since underdosing represents non-compliance with prescribed treatment, ICD-10-CM also contains codes that report some of the common underlying reasons for non-compliance such as:

• Intentional Underdosing of Medication Regimen Due Financial Hardship (Z91.120)
• Unintentional Underdosing of Medication Regimen Due to Age-Related Debility (Z91.130)
• Intentional/Unintentional Underdosing for Other Reason (Z91.128/Z91.138)
• Underdosing of Medication NOS (Z91.14)

External Cause of Morbidity codes (Y63.6, Y63.8-Y63.9) are also available to report the fact that underdosing is due to non administration of a necessary drug or failure in dosage during surgical and medical care.


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  1. mark schnepper May 10, 2016

    Is Z91.14 or Z91.19 or a different code appropriate for indicating that a patient declined taking a prescription?

    Hi Mark,
    Thanks for your question! The noncompliance code I would report for a patient who declines a prescribed medication is Z91.12; Patient’s intentional underdosing of medication regimen,  with a 6th digit that is dependent on the patient’s reason for declining the prescription; ‘”0” if the reason is financial hardship and “8” if the reason is something else.

    Hope this helps answer your question!

    Best wishes!

  2. Kelly Butler July 21, 2016

    What is the difference between coding noncompliance and underdosing?  If the reason is not given for the underdosing is there one that we defer to?

  3. coding support July 29, 2016

    Hi Kelly,
    Noncompliance is to be used when the patient had agreed to the regimen, and then does not follow-through.  Underdosing is if the patient is not taking the fully prescribed amounts. A reason for underdosing does not have to be spelled out, but more information can be helpful to determine how to properly code the scenario. 

    Hope this helps answer your question. Best wishes!

  4. Robynn August 18, 2016

    when physician documentation clearly shows that the patient isn’t taking medication and they document noncompliance as a diagnosis is it appropriate to include the underdosing as a final diagnosis?

  5. Grace Stewart November 12, 2016

    Hi I have a case where in the patient has past medical history of paroxysmal afib,HTN and CHF, home meds are amiodarone and aspirin.The patient was brought to ER due to rapid heart rate and he was diagnosed with Afib with RVR, it is also stated in the documentation that patient has non compliance with medication because he cannot afford the medicines. I just want to know If I can still code for the underdosing code and non-compliance code for this case or will I just code for the Afib because of the guideline: “If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.“My second question is If I will code for Afib, is it still ok to code for the noncompliance code? I hope you will answer my query. Thank you!

  6. Coding Support November 15, 2016

    Hi Grace,

    Thanks for your question.

    Coding this scenario requires 3 codes. The principal/first listed code will be the code for the A-fib. The guideline you referenced is just telling you that the underdosing code cannot be sequenced as the principal/first listed code, instead a code for the condition itself should be assigned as principal/first listed. An underdosing code and a noncompliance Z code are assigned as secondary codes, based on guideline C.19.e.5.(c) which states, “Noncompliance (Z91.12-, Z91.13-) or complication of care (Y63.6-Y63.9) codes are to be used with an underdosing code to indicate intent, if known”. Since the documentation states the patient is non-compliant with his meds due to lack of funds, the correct Z code is Z91.120; Patient’s intentional underdosing of medication regimen due to financial hardship.

  7. Marc D Grobman, DO November 17, 2016

    I understand the coding answer to Grace above, BUT since the HCFA form contains only 4 spots for coding an ICD10 code, do we use the Z91.xxx with ANOTHER CPT code, like 3008F?

  8. Coding Support November 29, 2016

    Hi Marc,

    Thanks for your follow-up question. I’m not sure I completely understand what you’re proposing. When you say “like 3008F” are you asking if you would assign code Z91.XXX in the same manner as or as an alternative to code 3008F or in addition to code 3008F?

    Thanks!


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