Coding Guidelines for Principal Diagnosis: A Comprehensive Guide for Inpatient Settings

Transitioning to inpatient coding requires a solid understanding of how to determine the principal diagnosis. Unlike outpatient settings, inpatient coding follows specific guidelines to ensure accurate representation of the reason for admission. As a facility coder, mastering the ICD-10-CM Official Guidelines for Coding and Reporting is paramount. These guidelines are divided into four key sections:

Section I: Coding Conventions and General Guidelines: This section lays the groundwork with essential coding conventions, general coding rules, and chapter-specific guidelines.
Section II: Selection of Principal Diagnosis: This section is dedicated to providing directives on how to accurately select the principal diagnosis (PDx).
Section III: Reporting Additional Diagnoses: This section outlines the criteria for reporting secondary diagnoses that coexist at the time of admission or develop during the hospital stay.
Section IV: Outpatient Services Coding: This section details the guidelines specific to coding and reporting outpatient services, which differs significantly from inpatient coding.

Beyond these official guidelines, healthcare facilities often implement internal coding guidelines to provide further clarity and address ambiguities within the ICD-10 code set. These internal guidelines are crucial for standardizing coding practices within an organization.

Navigating Section II for Principal Diagnosis Selection

The Uniform Hospital Discharge Data Set (UHDDS) provides the foundational definition for principal diagnosis in inpatient settings. According to UHDDS, the principal diagnosis is defined as: “The condition established after study to be chiefly responsible for occasioning the admission of the patient to the hospital for care.” Essentially, it’s the primary reason that led to the patient’s hospitalization. However, determining the principal diagnosis isn’t always straightforward. Section II of the ICD-10-CM guidelines offers detailed direction to navigate these complexities. Let’s break down the key subsections within Section II:

II. A. Symptom, Sign, and Ill-defined Condition Codes

Chapter 18 codes, representing symptoms, signs, and ill-defined conditions, should generally not be used as the principal diagnosis when a definitive, related diagnosis has been established. However, in situations where a definitive diagnosis cannot be determined after thorough investigation, assigning symptom or sign codes as the principal diagnosis becomes appropriate.

Example: Consider a patient admitted with chest pain. After extensive testing and ruling out all possible underlying conditions, if the definitive cause remains undetermined, then “chest pain” becomes the principal diagnosis.

II. B. Interrelated Conditions Potentially Qualifying as Principal Diagnosis

This section addresses scenarios involving two or more conditions that are interrelated and could each independently meet the criteria for principal diagnosis. This often includes conditions within the same ICD-10-CM chapter or manifestations typically associated with a specific underlying disease. In such cases, either condition can be sequenced as principal. Ideally, the choice should be guided by which condition was more resource-intensive or demanded more labor to treat.

II. C. Diagnoses Equally Meeting the Principal Diagnosis Definition

While less common, situations arise where two or more diagnoses equally satisfy the definition of principal diagnosis. In these instances, either condition can be sequenced first.

Example: A patient is admitted presenting with both chest pain and shortness of breath. The admitting diagnosis, after evaluation, is confirmed as both congestive heart failure and pneumonia. Both conditions are present on admission and are treated with equal intensity, for instance, using intravenous medications. To determine the most appropriate principal diagnosis, review the medical record to assess if one condition required a greater level of care in terms of resources, labor, or management. Furthermore, consult the ICD-10-CM tabular sections and AHA Coding Clinic for any specific sequencing instructions relevant to the conditions in question. Coding encoders like Codify by AAPC can be valuable tools in such scenarios.

II. D. Comparative or Contrasting Conditions

In certain less frequent cases, providers may document diagnoses as “either/or” conditions. When these comparative or contrasting conditions are confirmed, both should be coded, and either can be designated as the principal diagnosis. Consider these guiding questions when assigning the principal code:

What were the circumstances surrounding the admission?
Which condition was more resource-intensive or laborious to treat?

Note: Section II. E. Symptom(s) Followed by Comparative or Contrasting Diagnoses is no longer applicable as this guideline was removed in 2014.

II. F. Original Treatment Plan Not Executed

Even if the originally planned treatment is not carried out, the initial reason for admission remains the principal diagnosis.

Example: A 38-year-old woman is admitted for a scheduled elective cesarean section. Pre-operative medications are administered, but due to equipment malfunction, the procedure is cancelled, and the patient is transferred to another facility. The initial reason for admission, the elective c-section, remains the principal diagnosis because it was the condition that occasioned the admission.

II. G. Complications Following Surgery or Medical Care

When a patient is admitted due to a complication arising from surgery or other medical care, the complication itself should be coded as the principal diagnosis. If a code from the T80-T88 series lacks the necessary specificity to describe the complication, it should be followed by an additional code that specifies the nature of the complication.

II. H. Uncertain Diagnoses

In cases where the diagnosis at discharge is documented as “probable,” “suspected,” “likely,” “questionable,” “possible,” or uses similar terms indicating uncertainty, code the condition as if it exists. This guideline acknowledges the resource utilization involved in evaluating and ruling out these potential conditions. This guideline applies specifically to short-term acute care, long-term care, and psychiatric hospitals.

II. I.1 and I.2. Admissions from Observation Units

When a patient initially placed in medical observation is subsequently admitted as an inpatient due to a condition worsening or failing to improve, that condition should be assigned as the principal diagnosis. For admissions following post-operative observation, the condition responsible for the inpatient admission should be designated as principal diagnosis.

II. J. Admissions from Outpatient Surgery

If an inpatient admission directly results from a complication of outpatient surgery, the complication code is assigned as the principal diagnosis. In the absence of a documented complication, the reason for the outpatient surgery becomes the principal diagnosis for the inpatient admission. However, if a condition unrelated to the surgery is the true reason for inpatient admission, then that unrelated condition should be listed as the principal diagnosis.

II. K. Admissions/Encounters for Rehabilitation

For admissions specifically for rehabilitation, the condition requiring the rehabilitation services should be sequenced as the principal diagnosis.

Example: A patient with right-sided hemiplegia resulting from a cerebrovascular accident (CVA) is admitted for rehabilitation. In this case, code I69.351, Hemiplegia and hemiparesis following cerebral infarction affecting right dominant side, is the appropriate principal diagnosis. If the original condition is no longer active, assign the relevant aftercare code as principal diagnosis.

Example: A 68-year-old male with type II diabetes, COPD, and hypertension undergoes a left total hip arthroplasty for osteoarthritis. He is subsequently admitted for rehabilitation. Code Z47.1, Aftercare following joint replacement surgery, is the principal diagnosis in this scenario. For rehabilitation following active treatment of an injury, use the injury code with the appropriate seventh character indicating a subsequent encounter.

Additional Considerations for Principal Diagnosis Determination

Remember that ICD-10-CM coding conventions within the tabular listings take precedence over the general coding guidelines. Furthermore, the official ICD-10-CM Official Guidelines for Coding and Reporting supersede any internal facility guidelines or AHA Coding Clinic advice. Facility-specific internal guidelines, reviewed by compliance and legal departments, are valuable for promoting coding consistency, clarity, and standardization, ultimately reducing errors and ambiguities. Utilize these internal guidelines and AHA Coding Clinic as supplementary resources to enhance coding accuracy, ensure billing compliance, and optimize appropriate reimbursement. Payer-specific guidelines should also be considered, as they can vary.

It’s crucial to understand that the admitting diagnosis might not always be the final principal diagnosis at discharge. Throughout the patient’s stay, investigations and evaluations help determine conditions present on admission, confirmed diagnoses, and ruled-out conditions. Secondary conditions, those that coexist at admission, develop subsequently, or impact treatment and length of stay, must also be coded for comprehensive reporting. Diagnoses related to earlier episodes that have no bearing on the current admission should not be reported. Abnormal findings from laboratory, pathology, or diagnostic tests are not coded in the inpatient setting unless the provider explicitly indicates their clinical significance.

Avoiding Common Pitfalls

A critical mistake to avoid is coding solely from the discharge summary. A thorough review of the entire medical record for the admission is essential. This comprehensive review ensures that all relevant conditions, even those not mentioned in the discharge summary, are captured. It also allows for identifying clinical indicators that may necessitate a physician query for clarification. When reviewing operative reports, resist the temptation to code only from the preoperative or postoperative headings. The body of the operative note often contains crucial details that can enhance code specificity or justify reporting additional codes.

Resources:

FY 2018 ICD-10-CM Official Guidelines for Coding and Reporting; www.cms.gov/Medicare/Coding/ICD10/Downloads/2019-ICD10-Coding-Guidelines-.pdf
Uniform Hospital Discharge Data Set (UHDDS)

By diligently applying these Coding Guidelines For Principal Diagnosis and utilizing available resources, inpatient coders can ensure accuracy, compliance, and optimal reimbursement for their facilities.

Lee Williams

Leonta “Lee” Williams, MBA, RHIA, CPC, CPCO, CRC, CEMC, CHONC, CCS, CCDS, is the Senior Director of Education at AAPC. She brings over 20 years of extensive experience in health information management, serving as a coding director, auditor, educator, trainer, practice manager, and mentor. Lee is also the founder and past president of the Covington, GA local chapter and served as secretary on AAPC’s 2018-2021 National Advisory Board.

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