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Q&A: Determining Principal Diagnosis Selection

Analysis  |  By Revenue Cycle Advisor  
   February 27, 2021

Instruction can be found in Section II of the 2021 ICD-10-CM Official Guidelines for Coding and Reporting for "Selection of Principal Diagnosis."

A version of this article was first published February 26, 2021, by HCPro's Revenue Cycle Advisor, a sibling publication to HealthLeaders.

Q: When two conditions are both present on admission, both meet definition to be the principal diagnosis, and are "equally treated," my understanding is that the condition does not have to be "equally treated" in the sense of duration/frequency. Can you provide the actual verbiage of the coding rule and explain?

A: The instruction can be found in Section II of the 2021 ICD-10-CM Official Guidelines for Coding and Reporting for "Selection of Principal Diagnosis."

It states that the circumstances of inpatient admission always govern the selection of PDX. Furthermore, the guidelines refer to the rules outlined in CMS’ Uniform Hospital Discharge Data Set (UHDDS) as “that condition established after study to be chiefly responsible for occasioning the admission of the patient to the hospital for care.” The UHDDS definitions are used by hospitals to report inpatient data elements in a standardized manner.

The guidelines further state that in determining PDX, coding conventions in the ICD-10-CM Manual, the Tabular List, and Alphabetic Index take precedence over the coding guidelines.

Section II.C., contains rules governing code assignment for two or more conditions that equally meet the definition for PDX. It states that:

In the unusual instance when two or more diagnoses equally meet the criteria for principal diagnosis as determined by the circumstances of admission, diagnostic workup and/or therapy provided, and the Alphabetic Index, Tabular List, or another coding guidelines does not provide sequencing direction, any one of the diagnoses may be sequenced first.

CDI and coding professionals need to read the ICD-10-CM Official Guidelines for Coding and Reporting in its entirety, particularly the sections governing PDX selection.

To reiterate, first and foremost the selection of the PDX is based on the circumstances of the admission as stated above, followed by any instructions received in the coding conventions, such as a “code first” note (these instructions or conventions are only found in a code book) followed by the advice found in the ICD-10-CM Official Guidelines for Coding and Reporting, and lastly by any instruction/advice given in Coding Clinic, which is published quarterly.

There is no rule as to treatment having to be "equal." Sometimes the provider may determine no treatment (such as medication or surgery) is the best course of action for a patient, maybe monitoring the patient at a different level of care, for instance in the intensive care unit versus placement on a medical/surgical floor, is best. It really would depend on the circumstances of the admission.

Editor’s Note: Sharme Brodie, RN, CCDS, CCDS-O, CDI education specialist and CDI Boot Camp instructor for HCPro in Middleton, Massachusetts, answered this question. For information, contact her at For information regarding CDI Boot Camps, click here.

This answer was provided based on limited information. Be sure to review all documentation specific to your own individual scenario before determining appropriate code assignment.

Revenue Cycle Advisor combines all of HCPro's Medicare regulatory and reimbursement resources into one handy and easy-to-access portal. News is not just repeated from other sources. It is analyzed by our Medicare experts so professionals can comprehend any new rule and regulatory updates thoroughly. Learn more.

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