Structure of ICD-10-CM
ICD-10-CM codes are alphanumeric, ranging from three to seven characters, with the first character always a letter and the seventh character often representing an encounter type such as initial, subsequent, or sequela for injury and certain other codes. RHIA candidates are not expected to code at the depth of a CCS credential, but must understand overarching guidelines that affect data quality and reimbursement.
Selecting the Principal Diagnosis
The principal diagnosis is defined as the condition established after study to be chiefly responsible for the patient's admission. This is not necessarily the admitting diagnosis or the most severe condition, and candidates should be prepared to apply Uniform Hospital Discharge Data Set guidelines to scenario questions where multiple conditions are present.
Combination Codes and Excludes Notes
ICD-10-CM frequently uses combination codes that classify two diagnoses, or a diagnosis with an associated manifestation, in a single code. Excludes1 notes indicate two conditions that cannot be coded together because they are mutually exclusive, while Excludes2 notes indicate the excluded condition is not part of the code but the patient may have both conditions simultaneously, requiring both codes to be reported.
Coding Guidelines Hierarchy
Coders and HIM professionals must apply guidelines in order of authority: the ICD-10-CM Official Guidelines for Coding and Reporting take precedence, followed by Coding Clinic advice from the American Hospital Association, followed by facility specific policy, which cannot conflict with the higher authorities.
Present on Admission Indicators
Present on admission, or POA, indicators identify whether a condition was present at the time of inpatient admission. Accurate POA reporting affects hospital acquired condition payment policies and quality measure calculations, making it both a coding and a compliance concern.
Impact on Data Quality and Reimbursement
Inaccurate principal diagnosis selection or missed combination codes distort case mix index, DRG assignment, and quality measure outcomes. HIM leaders must monitor coding accuracy through regular audits and provide ongoing education as guidelines are updated annually each October.
Exam Tip
When a scenario presents multiple conditions treated during a stay, focus on which condition, after study, required the admission rather than which condition was most severe or was documented first, since these are common exam distractors.