The principal diagnosis is the condition established after study to be chiefly responsible for occasioning the patient's admission to the hospital for care. This is the UHDDS definition used in the ICD-10-CM Official Guidelines for inpatient principal-diagnosis selection.
“After study” is critical. The diagnosis initially suspected in the emergency department may change after diagnostic testing, consultation, treatment response, surgery, pathology, or other evaluation. The final principal diagnosis therefore may differ from the first diagnosis documented.
Relative weight does not determine principal diagnosis. A hospital cannot select a higher-paying condition merely because it produces a more favorable MS-DRG. Similarly, medication volume is not a principal-diagnosis criterion.
For CDI specialists, principal-diagnosis review requires understanding the circumstances surrounding admission, the diagnostic workup, final provider documentation, sequencing conventions, and any chapter-specific guidelines. When two conditions are documented and it is unclear which chiefly occasioned the admission, a provider query may be warranted.
The CCDS content outline specifically tests the principles and application of principal-diagnosis assignment.
CCDS Reference Topics: Principal diagnosis; UHDDS; inpatient sequencing; working MS-DRG.
=========
