It is crucial to emphasize on the importance of proper coding of diagnosis resulting in preciseness.

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Importance of Listing Primary Diagnosis Code
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Importance of Listing Primary Diagnosis Code
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The main purpose of a diagnosis is to determine, within a certain degree of accuracy, the underlying CAUSE
of the patient’s condition. It is very critical to stress the importance of proper medical coding of a diagnosis.
Accuracy, to the highest possible degree, is essential to reimbursement for services rendered; and to
protection from both malpractice and civil litigation. One often hears the term, principal diagnosis, primary
diagnosis, and first-listed diagnosis.
Coders are often confused, as with some healthcare providers, what term should be used, not only when,
but also under what circumstances of the patient. It is very important to understand the various
terminologies that are often used interchangeably dependent on the patient’s situation before applying
various terms.
The definition of principal diagnosis (originally developed in 1985) under the Uniform Hospital Discharge
Data Set (UHDDS) is said to apply only to inpatients during acute, short-term, long-term care and
psychiatric hospitals, dependent on the length of stay parameters.

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Importance of Listing Primary Diagnosis Code
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Below are the definitions of the different terms for principal diagnosis:
First-listed diagnosis:
Terms “principal” and “primary” are often used interchangeably to define the diagnosis that is sequenced
first. The term first-listed diagnosis/condition is used in the outpatient setting in lieu of principal diagnosis,
and because of the timing.
Moreover, in cases of an existence of a discrepancy, it is the first-listed diagnosis as per the coding
conventions of ICD-10-CM, along with the general and disease-specific guidelines within ICD-10-CM, which
will have precedence over the outpatient guidelines.
Outpatient surgery encounter rules are to assign the diagnosis code as first-listed for the condition that the
surgery was performed.

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Principal diagnosis:
Condition established after study to be chiefly responsible for the patient’s admission to the hospital. It is
always the first-listed diagnosis on the health record and the UB-04 claim form. This direction applies to
nursing homes as stated in the guidelines.
Primary diagnosis:
This term is often used to indicate the reason for the continued stay in the LTC facility. It is also used
interchangeably with the principal diagnosis.
The primary diagnosis should be listed first.
Other additional codes for any coexisting conditions are to be then listed. It should be remembered that,
your diagnosis—the disorder you are evaluating and/or treating—is considered the primary diagnosis and
should be listed first on the claim form.
Other supporting diagnoses are considered secondary and should be listed after your primary diagnosis. In
today’s medical parlance, Primary diagnosis is now termed as first-listed diagnosis.

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Dos and Don’ts when coding using the first-listed diagnosis
• Therapeutic services received only during an encounter/visit, the diagnosis should first be sequenced,
followed by the condition. Problem or other reason should be assigned as secondary codes. However,
when the primary reason is chemotherapy or radiation therapy, or rehabilitation, the exception here is,
the appropriate V code for the service should be listed first, and the diagnosis or problem for which the
service is being performed listed second.
• It has been stressed by the guidelines laid down that the outpatient surgery encounter rules are to
assign the diagnosis code as first-listed for the condition that the surgery was performed. But, in case
there is a difference between the postoperative diagnosis & the preoperative diagnosis when the
diagnosis is confirmed, the postoperative diagnosis or condition would be the most definitive diagnosis.
Thus, the first-listed diagnosis or condition is governed by circumstances of admission, reflecting the
reason the patient is present for the care.

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• It is noteworthy to understand here that, especially in the outpatient setting, codes for other diagnoses
(e.g., patients treated for chronic conditions including medication management) and care should be
sequenced as additional diagnoses and not as the first-listed diagnosis.
• Take note that, chronic conditions may not always be the reason the condition is treated during the visit.
But, the main reason for the visit, or what was addressed during the visit, should be the first diagnosis
listed. For instance, in the case of a patient with a history of asthma, if the physician codes the
exacerbation of the chronic condition – severe wheezing, coughing, chest tightness of breath, as the
first-listed diagnosis, the reason for the encounter and codes as secondary diagnosis chronic asthma,
the claim is likely to be reimbursed.
• The place of service should never dictate the diagnostic code, only the documentation.
• Do remember that E-codes assigned most regularly in the emergency department, should never be
assigned as a first-listed diagnosis.

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• When using V codes, usually implemented for occasions when circumstances other than a disease or
injury are recorded as a diagnosis or problem, they may be used as either a first-listed or as an
additional diagnosis, but depends on the circumstances of the encounter/visit. For instance, routine
outpatient prenatal visits which exhibit no complications V22.0, or V22.1, as the first-listed diagnosis can
be used
• If two or more diagnoses equally meet the definition for principal diagnosis, either diagnosis can be
sequenced as the first-listed diagnosis
• According to Medicare Rules, the principal (first-listed diagnosis) is the clinical diagnosis, in absence of a
definitive pathologic diagnosis, at the time a claim is filed
• Many of the codes may be interpreted as applying to more than one area with a slightly different
description relating that code to that anatomical area. There are very specific rules that must be
followed in the assigning of the codes. Medicare has historically set the precedent and standard which
all other carriers follow. Group insurance, HMO's, PPO's, auto insurers and worker's compensation, all
follow the precedents set by Medicare.

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FAQs
1. What is the importance of listing the primary diagnosis code first?
Listing the primary diagnosis code first ensures accurate documentation and reimbursement. It represents
the main reason for the patient’s visit or admission, which is crucial for proper coding, billing, and
protection against malpractice.
2. What is the difference between principal diagnosis, primary diagnosis, and first-listed
diagnosis?
• Principal Diagnosis: The main condition responsible for the patient's hospital admission, used primarily
in inpatient settings.
• Primary Diagnosis: Similar to the principal diagnosis, used to indicate the reason for continued stay in
long-term care facilities.
• First-Listed Diagnosis: Used in outpatient settings to describe the primary reason for the visit or service.

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3. When should the first-listed diagnosis be used?
The first-listed diagnosis should be used to represent the main reason for the patient’s visit or encounter,
especially in outpatient settings. It is also used in situations where multiple diagnoses are equally valid,
allowing any of them to be listed first.
4. How should diagnoses be sequenced for therapeutic services?
For therapeutic services, list the diagnosis related to the therapy or service first. If the main reason for the
visit is chemotherapy, radiation, or rehabilitation, list the appropriate V code for the service first, followed
by the diagnosis.
5. What should be done if there is a discrepancy between the preoperative and
postoperative diagnoses?
In such cases, the postoperative diagnosis should be listed as the first-listed diagnosis because it reflects the
most definitive condition after the procedure.

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6. Are chronic conditions listed as the first-listed diagnosis?
No, chronic conditions should not be the first-listed diagnosis unless they are the main reason for the visit.
The primary reason for the encounter should be listed first, with chronic conditions as secondary diagnoses.
7. Can E-codes be used as the first-listed diagnosis?
No, E-codes, which are used for external causes of injury or conditions, should not be assigned as the first-
listed diagnosis.
8. When should V codes be used?
V codes can be used as either a first-listed or additional diagnosis depending on the circumstances of the
visit. For example, routine prenatal visits without complications can use V22.0 or V22.1 as the first-listed
diagnosis.

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9. What is Medicare's role in determining the first-listed diagnosis?
Medicare guidelines set the standard for determining the principal diagnosis. In the absence of a definitive
pathologic diagnosis, the clinical diagnosis at the time of claim filing should be used as the first-listed
diagnosis.
10. What challenges can arise in medical billing related to diagnosis coding?
Challenges include credentialing, charge entry, payment posting, benefits/eligibility verification, prior
authorization, filing claims, AR follow-ups, managing old AR, claim denials, and resubmitting rejections.
For help with these challenges, Medical Billers and Coders (MBC) offers
comprehensive medical billing services and solutions.