The circumstances of inpatient admission always govern the selection of principal diagnosis. The principal diagnosis is defined in the 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".
In determining principal diagnosis the coding directives in the ICD-9-CM manuals, Volumes I, II, and III, take precedence over all other guidelines.
The importance of consistent, complete documentation in the medical record cannot be overemphasized. Without such documentation the application of all coding guidelines is a difficult, if not impossible, task.
Codes for symptoms, signs, and ill-defined conditions from Chapter 16 are not to be used as principal diagnosis when a related definitive diagnosis has been established.
Codes in brackets in the Alphabetic Index can never be sequenced as principal diagnosis. Coding directives require that the codes in brackets be sequenced in the order as they appear in the Alphabetic Index.
If the same condition is described as both acute (subacute) and chronic and separate subentries exist in the Alphabetic Index at the same indentation level, code both and sequence the acute (subacute) code first.
When there are two or more interrelated conditions (such as diseases in the same ICD-9-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.
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.
In those rare instances when two or more contrasting or comparative diagnoses are documented as "either/or" (or similar terminology), they are coded as if the diagnoses were confirmed and the diagnoses are sequenced according to the circumstances of the admission. If no further determination can be made as to which diagnosis should be principal, either diagnosis may be sequenced first.
When a symptom(s) is followed by contrasting/comparative diagnoses, the symptom code is sequenced first. All the contrasting/comparative diagnoses should be coded as suspected conditions.
Codes from the V71.0-V71.9 series are assigned as principal diagnoses for encounters or admissions to evaluate the patient's condition when there is some evidence to suggest the existence of an abnormal condition or following an accident or other incident that ordinarily results in a health problem, and where no supporting evidence for the suspected condition is found and no treatment is currently required. The fact that the patient may be scheduled for continuing observation in the office/clinic setting following discharge does not limit the use of this category.
Sequence as the principal diagnosis the condition which after study occasioned the admission to the hospital, even though treatment may not have been carried out due to unforeseen circumstances.
The residual condition or nature of the late effect is sequenced first, followed by
the late effect code for the cause of the residual condition, except in a few
instances where the Alphabetic Index or Tabular List directs otherwise.
Sequence first the code that reflects the highest degree of burn when more than
one burn is present. (See also Burns guideline 8.3)
When multiple injuries exist, the code for the most severe injury as determined by
the attending physician is sequenced first.
When admission is for management of an anemia associated with the malignancy, and the treatment is only for anemia, the anemia is designated at the principal diagnosis and is followed by the appropriate code(s) for the malignancy.
When the admission is for management of an anemia associated with chemotherapy or radiotherapy and the only treatment is for the anemia, the anemia is designated as the principal diagnosis followed by the appropriate code(s) for the malignancy.
When the admission is for management of dehydration due to the malignancy or the therapy, or a combination of both, and only the dehydration is being treated (intravenous rehydration), the dehydration is designated as the principal diagnosis, followed by the code(s) for the malignancy.
When the admission is for treatment of a complication resulting from a surgical procedure performed for the treatment of an intestinal malignancy, designate the complication as the principal diagnosis if treatment is directed at resolving the complication.
When coding a poisoning or reaction to the improper use of a medication (e.g., wrong dose, wrong substance, wrong route of administration) the poisoning code is sequenced first, followed by a code for the manifestation. If there is also a diagnosis of drug abuse or dependence to the substance, the abuse or dependence is coded as an additional code.
When the admission is for treatment of a complication resulting from surgery or other medical care, the complication code is sequenced as the principal diagnosis. If the complication is classified to the 996-999 series, an additional code for the specific complication may be assigned.