Coding Guidelines – Overview
The ICD-10-CM and ICD-10-PCS authoritative sources for coding and reporting are listed
below. These should be reviewed and referenced routinely for specific situations and
circumstances to ensure accurate coding.
1. ICD-10 Coding Classifications
2. Official Guidelines for Coding & Reporting (OCG)
3. AHA Coding Clinic
The instructions and coding conventions in ICD-10 take precedence over the Official Coding
Guidelines (OCG), which in turn take precedence over Coding Clinic advice. Coding Clinic
advice is the official source of advice where ICD-10 and the OCG are ambiguous, conflicting or
silent.
Coding Clinic for ICD-10 began in 2012. In the absence of changes to ICD-10 codes and
guidance, prior Coding Clinics will stand as long as there is nothing new published by Coding
Clinic to replace them.
When there is a discrepancy between the conventions in the classification, the guidelines, and/or
advice published in Coding Clinic, coding professionals should adhere to the hierarchy shown
above. Coding Clinic advises to submit any apparent conflicts with the specific case example(s)
and rationale to the AHA Central Office for review.
1. ICD-10 Coding Classifications. An example of an ICD-10-CM instructional rule are the two
Excludes Notes included in the Tabular List:
Excludes1 means “Not Coded Here.” The code excluded should not be used at the same time as
the code above the Excludes1 note. The two conditions cannot be coded together, except when
the two conditions are clearly unrelated to each other.
Excludes2 means “Not Included Here.” The condition excluded is not part of the condition it is
excluded from, but a patient may have both conditions at the same time. It is acceptable to code
both together.
Examples N39.0 Urinary tract infection, site not specified. Excludes1: Cystitis (N30.-). Codes
N39.0 and N30.- cannot be coded together. Cystitis is more specific than UTI.
D63.0 Anemia in neoplastic disease. Excludes2: Anemia due to antineoplastic chemotherapy
(D64.81). Both D63.0 and D64.81 can be coded together.
2. Official Coding Guidelines (OCG). The OCG includes specific guidelines regarding the
definition and selection of the principal diagnosis and secondary diagnoses:
"The definition for "other diagnoses" is interpreted as additional clinically significant conditions
that affect patient care in terms of requiring: clinical evaluation, or therapeutic treatment, or
diagnostic procedures, or extended length of hospital stay, or increased nursing care and/or
monitoring."
3. Coding Clinic. The purpose of Coding Clinic is to provide official coding advice and
clarification on code assignment based on the ICD-10 classification and Official Coding
Guidelines and provider documentation. It is outside the scope of Coding Clinic to determine,
,endorse or approve diagnostic criteria for any condition. Coding Clinic will not respond to any
questions regarding MS-DRGs, reimbursement, payment or coverage issues, or mediating
differences of opinion between providers and auditors or payers—unless it relates to the
application of specific coding guidelines or specific previously published coding advice.,
Coding Clinic advice is specific to the question asked and case scenario included. Do not
consider this general advice to be applied across the board. For example:
Question: A 94-year-old patient presented after being down on the floor for 8 hours. The patient
reported falling down steps after feeling weak. The provider's final diagnostic statement listed
"Rhabdomyolysis, dehydration and acute kidney injury." What is the appropriate code
assignment for rhabdomyolysis for this patient, traumatic or unspecified?
Answer: In this case, assign code M62.82, Rhabdomyolysis. Rhabdomyolysis is caused by the
breakdown of muscle tissue, resulting in the leakage of muscle contents into the blood. Since this
condition may occur secondary to traumatic injury or other non-traumatic causes (e.g.,
conditions that damage skeletal muscle), it is only coded as traumatic when the provider
explicitly documents "traumatic rhabdomyolysis."
Coding Guidelines - Principal Diagnosis
DEFINITION OF THE PRINCIPAL DIAGNOSIS
Official Coding Guidelines (OCG) Section II specifies rules for the selection of the principal
diagnosis, first noting that the definition is:
“That condition established after study to be chiefly responsible for occasioning the admission
of the patient to the hospital for care.”
The words “after study” in the definition are important, since it is not necessarily the admitting
diagnosis, but rather the diagnosis found after diagnostic workup (or surgery) that proved to be
the primary reason for or focus of the admission.
Consider WHY the patient was admitted to the hospital and could not be in observation or go
home. Many patients are admitted with several medical problems, but those that could have been
individually treated as an outpatient or observation are unlikely to be chiefly responsible for the
admission.
The condition (or at least some signs or symptoms referable to the condition) must have been
present on admission. But in some cases, it may be several days before the provider arrives at or
documents a definitive diagnosis. This does not mean that the condition was not present on
admission if the signs and symptoms of it were present on admission (POA).
The OCG POA Guidelines includes an important definition of POA with implications for
assigning the principal diagnosis: Diagnoses subsequently confirmed after admission are
considered POA if at the time of admission they "constitute an underlying cause of a symptom
that is present at the time of admission.”
The circumstances of admission always govern the selection of the principal diagnosis (unless
coding guidance states otherwise), and the selection of the principal diagnosis is based on the
entire medical record: “The entire record should be reviewed to determine the specific reason for
the encounter and the conditions treated.” (OCG p. 1).
Important considerations for determining circumstances of admission:
Severity of each condition or greatest mortality/complication risk
Complexity of care, evaluation, management, number/types of consultants
, Medications required, risks, route of administration (IV vs. po)
Diagnostic workup: Endoscopy, imaging, MRI/CT, ultrasound, catheterization; non-
routine laboratory tests
Intensity of monitoring (vital signs, nursing time, etc.)
Plans for follow-up care.
If treatment was totally or primarily directed toward one condition or only one condition would
have required inpatient care, that condition would be designated as principal diagnosis. In most
circumstances, the diagnosis for which a major or definitive surgical procedure is performed
would be assigned as the principal diagnosis. See topic Unrelated OR Procedure DRGs.
CODING RULES—PRINCIPAL DIAGNOSIS
1. TWO OR MORE DIAGNOSES THAT EQUALLY MEET THE
CRITERIA FOR PRINCIPAL DIAGNOSIS
“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 guideline does not provide
sequencing direction, any one of the diagnoses may be sequenced first.” (OCG Section II.C).
It is not uncommon for a patient to be admitted with multiple conditions. When management is
equally directed towards more than one condition and each condition would typically require
inpatient care, any one of the diagnoses can be assigned as principal diagnosis.
EXAMPLES
Pt admitted with CHF and pneumonia. Patient given IV Lasix and IV antibiotics.
Pt admitted with acute atrial fibrillation and acute heart failure. Patient is digitalized to reduce
the ventricular rate and given IV Lasix for systolic heart failure.
2. TWO OR MORE INTER
RELATED CONDITIONS, EACH POTENTIALLY MEETING THE DEFINITION OF
PRINCIPAL DIAGNOSIS
“When there are two or more interrelated conditions (such as diseases in the same ICD-10-CM
chapter or manifestations characteristically associated with a certain disease) potentially
meeting the definition of principal diagnosis, either condition may be sequenced first, unless
the circumstances of the admission, the therapy provided, the Tabular List, or the Alphabetic
Index indicate otherwise.” (OCG II.B).
EXAMPLE Patient admitted with SOB, chest pain, 4+ pitting edema, pain and erythema in
both legs. Found to have multiple bilateral pulmonary emboli due to extensive bilateral DVTs in
femoral and popliteal veins. Treated with IV heparin and discharged on Eliquis. Either PE or
DVT may be sequenced as principal diagnosis.
3. UNCERTAIN DIAGNOSIS
“If the diagnosis documented at the time of discharge is qualified as 'probable,' 'suspected,'
'likely,' 'questionable,' 'possible,' 'still to be ruled out,' 'compatible with', 'consistent with', or
other similar terms indicating uncertainty, code the condition as if it existed or was established.
, The bases for these guidelines are the diagnostic workup, arrangements for further workup or
observation, and initial therapeutic approach that correspond most closely with the established
diagnosis.” (OCG Section II.H).
This guideline is applicable only to inpatient admissions, not outpatient visits.
Exceptions: Code only confirmed cases of HIV, COVID-19, Zika, and certain influenza viruses
(J09-J10), e.g., H1N1, avian, etc.
Other terms that indicate uncertainty are "indicative of," "suggestive of," "comparable with,"
"appears to be" and "concern for." "Evidence of" is considered definitive, not uncertain.
"At the time of discharge" may mean in the final discharge note, when a consultant has signed
off, or in the discharge summary.
EXAMPLE RLL pneumonia possibly due to aspiration.” Assign code J69.0 for aspiration
pneumonia.
If an uncertain diagnosis is determined to not be present, not clinically supported, or obviously
ruled out at the time of discharge, it would not be coded. At the time of discharge may mean in
the final discharge note, when a consultant has signed off, or in the discharge summary.
For example, a code for “possible pneumonia” would not be assigned if negative CT scan and
antibiotics were discontinued before discharge or a full course of treatment.
"Borderline" diagnoses documented at discharge are considered confirmed (not uncertain) and
should be coded as such unless ICD-10 has a specific index term, e.g., borderline hypertension
(R03.0).
Impending or Threatened Condition. Any condition described at the time of discharge as
“impending” or “threatened” that actually occurred is coded as a confirmed diagnosis. If it did
not occur and there is a specific “impending” or “threatened” ICD-10 index term, assign the
given code. These are:
Impending coronary syndrome or myocardial infarction: Assign code I20.0, Unstable
Angina.
Impending delirium tremens: Assign code F10.239, Alcohol dependence with withdrawal
Threatened abortion/miscarriage: Assign code O20.0, Threatened abortion
Threatened labor (without delivery): Assign code O47.9, False labor
For all others, code only the existing underlying condition and not the condition described as
impending or threatened. For example, provider documentation of “impending stroke with
aphasia” and stroke was not confirmed, code only the aphasia.
4. CODES FOR SYMPTOMS, SIGNS, AND ILL-DEFINED CONDITIONS
“Codes for symptoms, signs, and ill-defined conditions from Chapter 18 are not to be used as
principal diagnosis when a related definitive diagnosis has been established.” (OCG Section
II.A).
EXAMPLE Syncope due to cardiac arrhythmia. Cardiac arrhythmia is the principal diagnosis,
syncope is a secondary diagnosis.
Do not assign a separate code at all for signs and symptoms that are routinely associated with a
disease process or when a related definitive diagnosis has been established (confirmed) as the
cause. See OCG Sections I.B.4 and I.C.18.a and b.