Determine the Principal Diagnosis Code in the Inpatient Setting

Determine the Principal Diagnosis Code in the Inpatient Setting

Making the leap to the facility side of coding? Be sure you can decipher which diagnosis is principal.

When transitioning from outpatient to inpatient coding, be sure you know the differences between the outpatient and inpatient guidelines when selecting principal and secondary diagnoses.
Facility coders should be well versed in all four sections of the ICD-10-CM Official Guidelines for Coding and Reporting:

  • Section I explains coding conventions, along with general coding and chapter-specific guidelines.
  • Section II gives directives on selecting the principal diagnosis (PDx).
  • Section III provides criteria for reporting additional diagnoses.
  • Section IV outlines guidelines for coding and reporting outpatient services.

In addition to the official coding guidelines, facilities will likely have their own, internal guidelines for you to follow when selecting principal and secondary diagnosis and procedural codes. Internal guidelines are valuable in clarifying some of the ambiguities that may exist within the ICD-10 code set.

Look to Section II for the PDx

Inpatient diagnoses are coded in accordance with the Uniform Hospital Discharge Data Set (UHDDS). UHDDS defines the
PDx as “The condition established after study to be chiefly responsible for occasioning the admission of the patient to the hospital for care.” In other words, the PDx is the condition primarily responsible for the patient’s admission. Many facility coders will tell you that determining this is not always straightforward.
Section II: Selection of Principal Diagnosis directs us in selecting the PDx code. Here is a breakdown of the guidance in Section II.

Section II. A. Codes for Symptoms, Signs, and Ill-defined Conditions

Codes from chapter 18 are not to be assigned as principal when a related, definitive diagnosis has been established.
There will be times when a definitive diagnosis cannot be determined. In these cases, sign/symptom code(s) may be assigned.
Example: Patient is admitted with chest pain. Multiple tests are ordered and performed, and all possible underlying conditions are ruled out. The PDx is chest pain.

Section II. B. Two or More Interrelated Conditions, Each Potentially Meeting the Definition for Principal Diagnosis

This includes diseases in the same ICD-10-CM chapter or manifestations characteristically associated with a certain disease.
Either condition may be sequenced first, but ideally you should determine which condition (if applicable) was more laborious or most resource-intensive to treat.

Section II. C. Two or More Diagnosis that Equally Meet the Principal Diagnosis Definition

This is not a common scenario. When it does occur, either condition may be sequenced first.
Example: A patient is admitted with chest pain and shortness of breath. The admitting provider’s definitive diagnosis lists congestive heart failure and pneumonia, both present on admission and both equally treated with IV meds.
Here also, you should review the medical record to determine if one condition required more attention, in terms of labor, resource, or management, over the other.
Check also for any specific sequencing instructions provided within the tabular sections of ICD-10 or by American Hospital Association’s AHA Coding Clinic.
An encoder, such as AAPC Coder ( will aid in these areas.

Section II. D. Two or More Comparative or Contrasting Conditions

This is not a common scenario but does occur at times. There may be occasions when a provider documents “either/or” conditions are confirmed. In these scenarios, both conditions are coded and either may be reported as principal. Some questions to consider when assigning the principal code:

  • What was the circumstance of the admission?
  • Which condition was more laborious (resource intensive)?

Note: You can skip over Section II. E. A Symptom(s) Followed by Comparative or Contrasting Diagnoses because this guideline was deleted in 2014 and is no longer applicable.

Section II. F. Original Treatment Plan Not Carried Out

The reason for the admission is still reported as principal.
Example: A 38-year-old female was admitted for elective c-section; pre-meds were administered, but due to equipment failure, the procedure was not performed, and the patient was transferred to another facility.
The previous c-section remains the PDx because it was the reason for the admission.

Section II. G. Complications Following Surgery or Other Medical Care

When an admission occurs due to a complication arising from surgery or other medical care, the complication code should be reported as principal.
Any code from series T80-T88 lacking the necessary specificity in describing the complication should be followed with a code for the specific complication.

Section II. H. Uncertain Diagnosis

If the diagnosis at the time of discharge is listed as “probable,” “suspected,” “likely,” “questionable,” “possible,” or another similar descriptive, code as if the condition(s) exists.
There is resource (expense) involved in working up or ruling out these conditions.
This guideline is applicable only to short-term, acute, long-term care, and psychiatric hospitals.

Section II. I.1 and I.2. Admission from Observation Unit

When a patient is admitted from medical observation for a condition that worsens or does not improve, assign that condition as principal.
For an admission following post-op observation, assign the condition that is responsible for the inpatient admission as principal.

Section II. J. Admission from Outpatient Surgery

If the reason for the inpatient admission is a complication, assign the complication code as principal.
If there is no documented complication, assign the reason for the outpatient surgery as principal.
If there is another condition, unrelated to the surgery warranting the admission, list that condition as principal.

Section II. K. Admissions/Encounters for Rehabilitation

Sequence the condition that requires rehabilitation as principal.
Example: A patient with right-sided hemiplegia following a cerebrovascular accident (CVA) is admitted for rehabilitation services.
Code I69.351 Hemiplegia and hemiparesis following cerebral infarction affecting right dominant side is the PDx.
If the condition is no longer present, assign the appropriate aftercare code.
Example: A 68-year-old male with type II diabetes, COPD, and hypertension underwent LT total hip arthroplasty due to OA. He is now admitted for rehab services.
Code Z47.1 Aftercare following joint replacement surgery is the PDx.
Note: For rehabilitation services following active treatment of an injury, assign the injury code with the appropriate seventh character for subsequent encounter.

Other Factors Weigh into the PDx

When determining the PDx, remember that ICD-10-CM coding conventions within the tabular listings take precedence over the coding guidelines. And the ICD-10-CM Official Guidelines for Coding and Reporting takes precedence over your facility’s internal coding guidelines and AHA Coding Clinic. Facilities should have internal guidelines (vetted by their compliance or legal departments) to help facilitate coding functions, promote clarity, and standardization within their coding department and reduce errors and ambiguity. Use these internal guidelines and AHA Coding Clinic advice as supplements to increase coding accuracy, reinforce billing compliance, and improve proper reimbursement. Also consider payer guidelines, which may vary from payer to payer.
Be aware that a patient’s admitting diagnosis may not end up being the same as the PDx at time of discharge. As the patient is worked up during their stay, you will determine which condition(s) were present on admission, which condition(s) were confirmed, and which conditions were ruled-out. For proper and complete reporting, secondary conditions should be coded. These are conditions that coexist at the time of admission, develop subsequently, or affect treatment and length of stay. Do not report diagnoses that relate to an earlier episode and have no bearing on the current admission. Abnormal findings (e.g., laboratory, pathology, diagnostic results, etc.) are not coded in the inpatient setting unless the provider indicates their clinical significance.

Watch Out for Traps

Don’t fall into the trap of coding solely from the discharge summary. The entire medical record for that admission should be reviewed. This ensures you do not miss reporting conditions present that were not captured on the discharge summary or miss the opportunity to issue a query based on clinical indicators found within the record. When reviewing the operative report, be sure to not code solely from the preoperative or postoperative headers; there is usually vital information within the body of the note which may help with code specificity or additional code reporting.

FY 2018 ICD-10-CM Official Guidelines for Coding and Reporting;
Uniform Hospital Discharge Data Set (UHDDS)

Medical coding books

Lee Williams
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Leonta (Lee) Williams, MBA, RHIA, CCS, CCDS, CPC, CPCO, CRC, CEMC, CHONC, is director of medical coding, Georgia Cancer Specialists and Healthcare Management Consultant, Karna, LLC. She has more than 18 years health information management experience as a coding director, auditor, educator, trainer, practice manager, and mentor. She has provided coding leadership and oversight on programs sponsored by the Centers for Disease Control and Prevention, National Center for Health Statistics, the U.S. Consumer and Product Safety Commission, and Industrial Economics, Inc. Williams has extensive experience in regulatory compliance, CDI, and risk management. She is founder and past president of the Covington, Ga., local chapter and currently serves as secretary on the National Advisory Board.

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